Cynthia A. Challener is a contributing editor to Pharmaceutical Technology.

Cynthia A. Challener

Coprocessed excipients are blends of different excipients subjected to physical processing that leads to modifications of their physical structures without causing any chemical changes. They possess unique functionality that cannot be achieved through simple blending and are increasingly important for addressing formulation issues posed by the highly complex APIs under development. Adoption of coprocessed excipients has been slow, however, because even when prepared using compendial excipients, they are considered “novel” by regulators. The lack of a separate excipient approval process means that drug developers must take on elevated risk when using such “novel” excipients in the formulation of drug candidates.

Reducing complexity and increasing functionality

Oral solid dosage forms are traditionally formulated with combinations of individual excipients with differing functionalities (filler, binder, disintegrant, lubricant, flow-aid, solubilizer, etc.), says Ashish Joshi, pharma technical and business manager at BASF Pharma Solutions. The processes used to formulate these excipients into an oral dosage form are complicated as well as time-, energy-, and labor-intensive (e.g., granulation, spray-drying, roller compaction, etc.). In addition, the use of many individual excipients requires bracketing or optimization studies and has the risk of non-uniform distribution, which can adversely affect final product performance.

The ideal process for tablet formation is direct compression, as it eliminates the need for granulation or other prior processing steps, according to Joao Marcos Assis, global technical marketing manager, BASF Pharma Solutions. “Direct compression formulations, however, typically require multiple excipients to achieve good flowability, high bulk density, excellent compressibility, and fast disintegration (for immediate release formulations) because individual materials do not possess these multiple attributes,” he observes.

Coprocessed excipients can be used to overcome these formulation challenges through their enhancement of the resulting material’s performance and processability, Assis says.“By reducing manufacturing complexity and thus drug development time, coprocessed excipients can significantly expedite time-to-market,” he continues. Furthermore, API and coprocessed excipients normally fulfill the minimum functional requirements for tableting, consolidating quality-by-design efforts by simplifying the formulation. Analytical testing and material handling and warehousing needs and documentation requirements are also reduced.

The benefits of using coprocessed excipients are increased when multiple excipients can be coprocessed together. “Initially, most coprocessed materials were based on just two excipients, but increasingly coprocessed products being introduced to the market comprise multiple excipients,” notes Yeli Zhang, technical service manager at IFF Pharma Solutions.

The ability to combine many individual excipients and functionalities into a single high-functionality excipient enhances the ease of formulation and final performance as well as enables process simplification and cost-savings, Joshi adds. “Consequently, the major trend in developing coprocessed excipients is to reduce the number of individual excipients used in a formulation, with a focus on improving the flow-properties, compressibility, disintegration, and lubrication of oral solid dosage forms using a single coprocessed excipient,” he comments.

This trend is particularly true with coprocessed excipients intended for us in orally disintegrating tablets (ODTs). “Many companies are launching coprocessed excipients targeting this segment that combine a number of excipients because ODT formulations require a high number of excipients and are typically formed using direct compression,” adds Vinay Muley, research and development leader at IFF Pharma Solutions. Joshi agrees that single coprocessed excipients can provide not only good flow,
compressibility, and fast-disintegration, but also excellent taste and a pleasant, non-gritty mouthfeel.

Coprocessed excipients are also increasingly being used to convert more complicated, labor-intensive formulation processes such as wet granulation into quicker direct-compression processes without affecting the final product quality or performance, according to Joshi. He also notes that coprocessed excipients are being used to improve the efficiency of continuous manufacturing operations given that only a limited number of feeder ports are typically available and it is crucial to precisely control the flow-rate of excipients as they are added.

Developers of coprocessed excipients can theoretically use any material in their products, but most commonly, excipients that already have pharmacopeial monographs are selected because these excipients have a history of being used in pharmaceutical product formulations, according to Zhang. The key when selecting different ingredients to use in a particular coprocessed excipient is to choose those materials that will provide the functionality required to address customer needs, Zhang observes. Coprocessed excipients can improve drug processability and/or drug product performance. “Mainly excipient developers are looking to solve particular customer problems or provide particular benefits, and excipients are chosen that can maximize the needed functionality,” she says.

Ideally, adds Muley, the materials used to create coprocessed excipients will also have synergistic interactions that lead to enhancements in functionality, so that the coprocessed excipient will not only simplify formulation, but provide improved performance. Joshi adds that in addition to having complimentary and/or synergistic functionalities, the individual excipients chosen should be amenable to use in commonly available commercial processes (agglomeration, spray-drying, etc.) and behave reproducibly under the processing conditions. Ingredients used in coprocessed excipients also need to be nonreactive and inert so they do not undergo any chemical changes during production, according to Muley.

Typically, one or more fillers are coprocessed with binders, glidants, or disintegrants depending on the intended purpose of the product, according to Diogo Gomes Lopes, product development scientific team leader, Softgel and Oral Technologies at Catalent. “Coprocessed excipients that are intended to overcome any manufacturing limitations of the API, such as poor compressibility or poor flowability, are often composed of fillers, which are coprocessed with binders or glidants,” he explains. These types of coprocessed excipients also have the potential to increase drug loading in the drug product, allowing for production of a smaller dosage form that is more acceptable to the patient, Gomes says.

Some coprocessed excipients specifically aim to improve the performance of the drug product. Here again, Gomes points to coprocessed excipients for the manufacture of ODTs. “These coprocessed excipients allow for immediate disintegration of the tablet after administration while providing sufficient mechanical strength for packaging and transport,” he notes.

The materials chosen for coprocessing can include both small molecules, such as sugars and esters, and polymers such as polyvinyl acetate copolymers, microcrystalline cellulose (MCC), and starch. Coprocessing such varied materials together can lead to improved functionality, including greater processing properties as well as improved content uniformity, palatability, stability, and enhanced sustained-release performance.

Processing methods provide intimate mixing

Several methods are used to manufacture coprocessed excipients. The one feature they all have in common, according to Zhang, is that they involve physical processing of two or more excipients such that they interact with each other on a micro level, providing intimate mixing.

The most common methods include spray drying, flash drying, co-extrusion, granulation, high-shear granulation, fluid bed granulation, and roller compaction. “All of these processes are well known and are standard operations in pharmaceutical manufacturing,” Assis underscores. The key advantage is that under the mild conditions—moderate temperature and pH values, for example—chemical reactions between the ingredients can generally be excluded. It is important, he emphasizes, to determine the potential for incompatibilities between the different excipients used that could lead to chemical changes and avoid any combinations that might present reactivity concerns.

One exciting new method that could play a role in the production of coprocessed excipients, according to Muley, is 3D printing. Fused deposition modeling, he notes, is a good example of an additive manufacturing method very applicable to the production of coprocessed excipients. “The use of such methods is at the very preliminary stage, with exploration of the technology just beginning,” he says. Such approaches fit well with the push by FDA to adopt more efficient production technologies.

Although the development of coprocessed excipients does not involve combinatorial chemistry to impart many different chemical and molecular changes, there still are a large number of excipients to choose from. “Increasing functionality by modifying physical interactions only can present challenges, and pre-formulation studies using a design-of-experiment (DoE) strategy can be very helpful at the initial development stages,” Muley observes.

Computational methods can also be used to better support formulators during the development of drug products using coprocessed excipients, according to Silke Gebert, project engineer, BASF Pharma Solutions. For example, she points to ZoomLab, BASF’s Virtual Formulation Assistant for predicting and optimizing formulations using advanced algorithms and thereby expediting drug development. “Marketed coprocessed materials, new products, and prototypes can be characterized using the ZoomLab-logic to generate a chart that identifies each material’s favorable and less favorable properties, such as particle size distribution, compressibility index, and flowability,” she explains.

The need to accelerate drug development and also increase the efficiency and reduce the cost of drug manufacturing is driving excipient suppliers to seek more comprehensive coprocessed product solutions. “The most significant development in the coprocessed field relates to the growing focus on all-in-one coprocessed excipients,” Gebert contends.

All-in-one excipients, Gebert explains, are strategically designed multifunctional materials containing all the functionalities required to produce tablets: diluent/filler, disintegrant, binder, and lubricant at a minimum. “These materials are processed to achieve optimal bulk density, flowability, blend processability, drug uniformity, excellent compressibility, fast disintegration, and outstanding product performance,” she says. The drug manufacturing process then only requires blending the API and the all-in-one coprocessed excipient, then compressing the blend.

For these all-in-one products, Assis notes that common fillers include lactose, mannitol, and MCC; binders are often PVA-polyethylene glycol copolymers, PVP, or pre-gelatinized starch; disintegrants can be crospovidone, croscarmellose, or starch glycolate; and lubricant choices include sodium stearyl fumarate and magnesium stearate.

“Each ingredient in these compositions needs to be expertly selected with the end-use in mind,” Assis stresses. Furthermore, the excipient manufacturing process needs to be designed specifically to reduce chemical and physical instabilities.

Continuous tableting processes will benefit the most from the use of all-in-one coprocessed excipients, says Assis. “In order to reduce variability and dosage accuracy issues during the continuous manufacturing process, it is crucial to have a highly stable and controlled feed rate. With an all-in-one coprocessed excipient, rather than five feeders for the API, binder, filler, disintegrant, lubricant, only two are required for the API and the all-in-one coprocessed material, affording a more straightforward process,” he explains.

In addition, because coprocessed excipients reduce blend variability, they can contribute to reduced sampling and analytical errors for continuous processes monitored using inline/online/atline sensors, according to Assis. “Process analytical technology is increasingly being used during formulation development as well as in manufacturing. Coprocessed excipients have been shown to be less sensitive to shear, and due to their coprocessed multicomponent nature, the blend has lower intrinsic variability. In effect, this leads to more accurate and robust PAT [process analytical technology] models that do not require extensive model maintenance and updates,” he observes.

Regulatory hurdles present biggest challenges

Beyond demonstrating that individual ingredients in coprocessed excipients have not undergone any chemical changes, there are a few other challenges to developing new coprocessed solutions. One, according to Zhang, is that coprocessed excipients have fixed ratios of the various ingredients and as a result they may not be as broadly applicable as simple blends of excipients. “The current solution for this challenge is to design the coprocessed excipient in a way so that it meets the majority of needs,” she says. They are also designed as fit-for-use.

Manufacturing coprocessed excipients that are truly highly functional is not easy either, Muley adds. “A deep understanding of the problem or issue that will be addressed by the coprocessed excipient and proper research and development efforts are both required to ensure that new coprocessed excipients are highly functional and produced using a robust manufacturing process,” he comments.

It is important, for instance, to understand and control the variability of the excipient’s material attributes, according to Dejan Lamešić, head of formulation and process development, Softgel and Oral Technologies with Catalent. “Doing so further supports pharmaceutical users in determining the potential impact of an excipient on a final drug product,” he says.

The higher cost of coprocessed excipients can be an issue as well, Lamešić notes. “Coprocessed excipients must demonstrate sufficient manufacturing process efficiency for customers,” he says. The uniqueness of coprocessed excipients, meanwhile, can be a concern for drug formulators from a security-of-supply perspective. “The excipients are usually only available from one supplier, which can increase supply risk and impact an innovator’s supply chain strategy,” Lamešić explains.

The biggest challenge to the adoption of coprocessed excipients, however, is a regulatory one. “Despite the significant positive feedback we have received about coprocessed excipients, there is a reluctance on the part of drug formulators to use these ‘novel’ excipients because of the higher risk they represent with respect to the regulatory approval process,” says Zhang.

The fact that many coprocessed excipients do not have an official monograph available is one of the major obstacles to their wider adoption in drug products, agrees Lamešić. “Although there have been developments in recent years, including the ongoing development of a general monograph on coprocessed excipients and guidance from the International Pharmaceutical Excipients Council on these products, there are still regulatory hurdles that need to be resolved,” he observes.

One of the fears surrounding the use of coprocessed excipients for formulators has been that regulatory agencies may request additional data to support the safety and efficacy of these materials, adds Joshi. He does note, however, that lately pharma companies have realized they cannot develop the drugs of tomorrow using traditional excipients that were developed decades ago.

In addition, Joshi points out that excipient manufacturers have put into place robust manufacturing and quality control mechanisms to ensure reproducible manufacture of high quality, coprocessed excipients. There is also significant regulatory support provided with Type IV drug master file (DMF) filings and well-documented analytical procedures. He also notes that FDA’s new pilot program to evaluate and approve new excipients before they are used in a drug filing is a significant positive step. “All these factors have significantly increased the acceptance and use of coprocessed excipients by the pharma industry, leading to their increasing use in FDA-approved formulations,” he concludes.

Continued growth with improved robustness

Despite these regulatory hurdles, the drive to reduce the time and cost for new drug development will continue to make coprocessed excipients attractive and lead to their growing use, according to Muley. The ability of these materials to help drug makers produce more robust oral solid dosage forms by overcoming manufacturing process challenges and reducing variabilities will also keep interest levels high, adds Assis. Growth will increase at an even greater rate if a regulatory pathway for coprocessed excipient approval is established, Zhang notes.

Cynthia A. Challener is contributing editor to 


Vol. 46, No. 6
June 2022
Pages: 24–26, 49

When referring to this article, please cite it as C. A. Challener, “Development of Coprocessed Excipients,” 

Articles

The right processes used with the right excipient combinations address evolving formulation needs.

Development of Coprocessed Excipients

Inhaled drug formulation involves consideration of multiple factors, including the properties of the API, the needs of the target patient population, the delivery requirements, and the choice of device. Predicting the performance of a specific API is, consequently, quite challenging. While some computational approaches can help, physical experiments provide the greatest insights.

Increasing applications for inhaled delivery

Historically, the inhaled route has been preferred for the local administration of drugs to treat pulmonary diseases. “Inhaled delivery has clear advantages because delivering the API directly to the intended target allows for more efficient delivery of less overall dose with maximized efficacy and minimized dose-related side effects when compared to simpler systemic dosing,” explains Mark Parry, technical director with Intertek Melbourn.

Inhaled delivery also provides an alternative route for systemic dosing with different pharmacokinetics when compared to traditional routes such as solid oral dose and is of increasing interest where rapid delivery and onset of action is the objective, Parry adds. APIs that have stability issues upon contact with gastrointestinal fluids or decreased bioavailability because of first-pass metabolism can also be considered for inhaled delivery, notes William Wei Lim Chin, manager of global scientific affairs at Catalent.

Today, this route of administration can also be used to deliver systemic drugs for indications such as diabetes, Parkinson’s disease, and for pain management, according to Chin. “The large surface area in the lungs and the thin-walled pulmonary vasculature allow transport of drugs into the bloodstream,” he explains.

Even large molecules such as peptides, antibodies, and various types of engineered proteins can now be delivered via the lungs, Chin observes. These molecules present considerable challenges for delivery via the traditional oral route. “As we see increasing importance of new modalities in the biopharmaceutical space coming through the drug development pipelines, inhalation provides an alternative to parenteral delivery of these active substances that may provide advantages both in terms of the pharmacokinetic behavior and the patient experience,” Parry states.

Indeed, one of the primary factors in determining if formulation for inhaled delivery is the right approach—and the specific type of inhalation device—for any given API is the needs of the target patient population. “If the device does not meet the needs of the patient population, the utility of the product will be severely limited,” observes Jennifer Wylie, director of analytical research and development at Merck.

For instance, while there is evidence that patients prefer inhaled products to injectable ones (1), inhaled devices are usually more complicated to use than oral or injectable dosage forms, Chin notes. “Strategies that include patient education or training can help to address these limitations, as can careful design or selection of the delivery device,” he says.

In another example. Wylie points to the fact that dry-powder inhalers (DPIs) cannot be used by children younger than five to six years of age. “If the indication being addressed has a significant pediatric population, it may therefore be necessary to select an alternate device that is more appropriate, such as a nebulizer,” she comments.

Parry adds that a nebulizer formulation for a soluble API could be the simplest route to develop and, if only used in a hospital setting for short-term treatment, may be well tolerated by the patient and make the most sense commercially. When looking at the management of chronic diseases such as asthma and chronic obstructive pulmonary disease (COPD), however, he comments that the benefits of multidose DPI and pressurized metered-dose inhaler (pMDI) products become more important. Furthermore, engaging in more complex development programs can make commercial sense when considering large patient populations.

In addition to considering the needs of the patient population, Chin points out that whether or not inhalation delivery is the correct choice depends on the desired site of action (local versus systemic), whether there is a need for rapid absorption, and the drug class, all of which must be balanced against the development costs associated with these relatively complex products.

Specific attributes of an API that can affect its suitability for inhalation delivery include its physicochemical and interfacial properties, the ease and robustness of its manufacturing process, its inherent stability and potential routes of degradation, the level to which it interacts with its biological target and how long it is retained in the lung, its local and systemic bioavailability, and its toxicity, according to Charles Evans, senior vice president of pharmaceutical development for MedPharm.

Other factors that are typically considered when selecting inhalation delivery as outlined by Marc Brown, co-founder of MedPharm and chair of the company’s scientific committee, include the intellectual property status; the funds available for formulation development; the main objective of the project (i.e., proof of concept or full commercial development); the delivery device; and the potential processing/production needs of the API, such as micronization, spray drying, freeze drying, coacervation, etc.

Because there are so many diverse classes of APIs considered for inhalation delivery, defining an ideal set of API properties is difficult. “With various platforms and production technologies available, almost any API candidate can be formulated for inhalation,” Chin observes. He does note, however, that certain overarching molecular properties will enable more successful delivery to the lung, such as the nature of the solid state, the level of permeability, and the specific surface area.

In fact, the ideal properties of an API do depend on the specific delivery device, according to Wylie. “Usually, a solution formulation is desired for a nebulizer, and therefore a stable molecule with adequate solubility is desired.For a dry powder inhaler, the ability to reduce its particle size to the appropriate size range is important,” she adds.

One of the first properties to consider for an API when deciding on a type of delivery, Parry agrees, is how soluble the material is, including related salt forms. Equally important is how practical particle engineering such as micronization or spray drying might be, which can be impacted by properties such as the melting point and any characteristic polymorphism. “These considerations will guide the feasibility and likely complexity of the different delivery options,” he says.

Brown adds that APIs with higher aqueous solubilities can be more applicable to nebulizer systems, including both portable and hospital units. “Nebulizer formulations can quite often be a faster route to clinical studies for proof of concept as they leverage the simplest approach,” he adds.

APIs that are soluble in more polar solvents such as alcohols, meanwhile, are often more suitable for MDIs, Brown says. Those with attractive interfacial properties, particularly post-micronization, can be appropriate for DPIs and suspension formulations. He also emphasizes that crystalline materials with good chemical and physical stability are preferred. A thorough understanding of the particle size and its aerodynamics is required for small-molecule APIs delivered via carrier-based or carrier-free DPIs, Chin adds. When an excipient carrier is involved, he stresses that particle-to-particle interactions, particularly the API morphology/shape and surface characteristics, are critically important.

The requirements for small and large molecules intended for inhalation formulations do differ somewhat. For small molecules, Chin notes that properties centered on the solid state of the drug (crystalline for stability purposes versus amorphous for solubility improvement), permeability, and particle size are critical drivers in influencing the drug absorption process in the lung. He adds that it has been reported that small-molecule inhalable drugs generally meet Lipinski’s Rule of Five, with a tendency to have slightly higher molecular weights, high polar surface areas, and lower lipophilicities (2).

For large molecules such as peptides, proteins, and antibodies, Chin observes that particle surface properties are probably more critical criteria for the disposition and retention of these molecules in the lung. Because of the structure of these large molecules, they are more amenable to formulation using a spray-drying process for dry-powder formulations.

“Most important,” Chin contends, “regardless of the type of API and delivery platform, is the ability to repeatedly and consistently deliver the drug molecules as an aerosol.”

Inhaled drug delivery is inherently complex requiring identification of compounds with an appropriate balance of lung retention, toxicity, and bioavailability according to Evans. Several studies have correlated an API’s physicochemical properties with the absorption of inhaled drugs, but Chin notes the current consensus is that there is a lack of reliability of in vitro methods to establish absorption and permeability at the lung level.

“For dry powder inhalers, the particle size of the API must be of a respirable size (usually considered below 5 microns).For any solution formulation (for example, a nebulized solution), the API must have adequate solubility in the proposed formulation. Other than that, it is difficult to predict the performance without any experimental data,” Wylie says.

The pulmonary biopharmaceutics classification system (pBCS), introduced in 2010 and inspired by the oral biopharmaceutics classification system (BCS), attempted to establish a framework by considering the physiology of the lung, drug physicochemical properties, and drug absorption (3). The pBCS, Chin explains, suggested that molecular size, lipophilicity, solubility, acid dissociation constant (pKa), protein binding, polar surface area, and number of rotatable bonds predict an API’s permeability across the lung epithelium.

“From the developability perspective, this was a turning point that generated considerable interest from academia, industry, and regulatory stakeholders,” Chin says, pointing to a workshop on the topic (4). Unfortunately, he observes that 12 years on, the predictive utility of the pBCS framework remains uncertain as there are still many factors other than physicochemical properties that affect drug disposition in the lung, including the variability in patient breathing patterns and compliance to treatment regimens.

On a positive note, MedPharm has found that some cell- and tissue-based models developed in-house at the company can be used to provide a means of comparing performance between APIs and devices, according to Evans.

Parry also points to significant research into better models for understanding the way APIs are deposited in the lungs and then dissolve, which could help improve in-vitro/in-vivo correlation. “While much of this work has been driven by a need to better support the development of generics, we now have an increasingly broad toolbox to understand and study the delivery of poorly soluble APIs that can aid the particle engineering and formulation development work in optimizing their performance,” he remarks.

Computational approaches for aiding inhalation formulation development are being investigated, but developing effective models is not easy. “Development of inhalation products relies heavily on the packaging and delivery device, not only the formulation, so understanding the behavior using computational methods can be very complex,” Brown observes.

Mathematical/computational models for predicting airflow and respiratory aerosol deposition have been reported in the literature, but Brown believes, like many such models, they have significant limitations due to the gross assumptions they require. He does expect the value of these models to increase over time, however, especially for large pharmaceutical companies with libraries comprising thousands of APIs and drug formulations available for screening.

One example is Cohesive Adhesive Balance (CAB), a screening tool for investigating the surface interfacial properties of secondary processed micronized APIs and their influence on blending dynamics, stability, and in vitro performance. “CAB directly quantifies the relative magnitudes of the cohesive and adhesive forces that govern formulation structure and ultimately product functionality,” Brown explains. It can be used throughout API process development, early-phase DPI formulation development, and scale-up.

Chin points to thermodynamic modeling approaches for predicting process parameters that affect the properties of spray-dried particles and computational fluid dynamics (CFD) simulations for understanding the complexity of device and formulation interactions, which he says are being used to improve the performance of DPIs. CFD has more recently been used to study air flow within devices and patients, while discrete element methods are used to simulate dispersion and aerosolization of particles, according to Brown.

Inhaled delivery development is primarily focused on getting efficient dosing of drug to the right area of the lung. “Particles larger than 5 microns may not travel very far into the lung, particles in the 3-5-micron range will tend to deposit in the larger airways, while sub-3-micron particles will reach the deeper lung; the desired target will depend on the API and the condition being treated,” Parry says.

Ultimately, therefore, developing effective inhalation formulations requires extensive physical evaluation and experimentation, Wylie agrees. “The API and its physicochemical characteristics can directly impact the performance of an inhaled product.It is very important to gain understanding of these properties throughout development,” she states.

In general, optimizing for the right particle size may have trade-offs in overall dose amounts delivered to the lung, so optimization for the overall product performance can be complex, observes Parry. “When dealing with solid APIs (DPI or suspension-based products), therefore, understanding the physical properties and behaviors will greatly inform the development objectives,” he says. Having early empirical data from well-designed feasibility and scoping studies is essential.

Typical experiments include solubility and stability studies, as well as extensive analysis to determine particle size, shape, and density; crystallinity, surface morphology, and polymorph content; and the molecule fingerprint of the API, according to Evans. Using these data, the best delivery routes are determined and preliminary formulations and devices are developed simultaneously.

“The specific approach for any given API and project depends on the data that [are] available,” Evans adds. For example, if particle-size data are available, then it is possible to assess whether the distribution will be suitable for an inhalation formulation or if micronization is required. However, he also notes that the potential for successful micronization is more difficult to predict without an understanding of the interfacial properties, which relate to the likelihood of agglomeration at smaller particle sizes. Solubility and stability data, meanwhile, can indicate whether a solution nebulizer system or MDI would be a more viable delivery platform.

Even though gathering experimental data is challenging, it is essential to the development of inhaled delivery formulations. Fortunately, evidence-based models do show promise for improving the development process, including proprietary in-house solutions as well as solutions accessible by the wider stakeholder community.

2. T.J. Ritchie, C.N. Luscombe, and S.J.F., 

4. Hastedt, et al. “Scope and Relevance of a Pulmonary Biopharmaceutical Classification System,” AAPS/FDA/USP Workshop March 16-17th, 2015 in Baltimore, MD. AAPS Open 2, 1 (2016).

Cynthia A. Challener, PhD, is contributing editor to 


Volume 46, Number 5
May 2022
Pages: 22–25

When referring to this article, please cite it as C. Challener, “Inhalation Formulation Development: Predicting API Behavior,” 

Inhalation formulations are complex, and empirical data are essential for realizing optimal solutions.

Inhalation Formulation Development: Predicting API Behavior

Drug products must be produced in a manner that ensures both their safety and efficacy. That requires consideration of the quality of all ingredients in a final formulation, including all excipients, whether they are functional or inert.

“Excipients are critical to the safety and efficacy of nearly every drug product, if not all drug products, regardless of route of administration,” says Joseph Zeleznik, technical director, North America at IMCD Pharma. They can impact drug substance solubility and permeability, stability, release rate, and absorption. Variability in excipients therefore needs to be part of the formulation risk assessment.

Evaluating how excipients affect performance is essential to ensuring drug product performance and achieving therapeutic success. Leveraging excipient supplier expertise facilitates pharmaceutical development processes. Good two-way communication contributes to the risk assessment and experimental design to obtain the enhanced understanding of formulation components and processing required quality-by-design (QbD) approaches.

The need to manage excipient complexity and variability

Excipients are complex materials typically made up of multiple components, which vary from batch to batch and supplier to supplier, according to a International Pharmaceutical Excipients Council (IPEC)-Americas panel comprising Brian Carlin (owner of Carlin Pharma Consulting), Chris Moreton (principal consultant at FinnBrit Consulting), David Schoneker (president/owner/consultant of Black Diamond Regulatory Consulting), Katherine Ulman (primary at KLU Consulting), and Joseph Zeleznik. In addition, residual and trace materials can change between excipient manufacturers, says Krizia M. Karry, head of global technical marketing for BASF Pharma Solutions.

“Due to the multi-component nature of excipients, what drives excipient performance depends on its intended application,” Karry observes. For example, she notes that a co-processed excipient may enable direct compression of fast-dissolving tablets, but if its chemical composition or physical properties change within the allowed ranges, there could be an effect on tabletability or disintegration.

“QbD,” the IPEC-Americas panel states, “requires a more in-depth understanding of the excipient beyond the traditional compliance with (sales) specifications.” That includes the impacts of excipient lot-to-lot variability and changing excipient suppliers, adds Zeleznik. Therefore, he contends, if excipients are not included as part of a QbD approach, their impact on the API and, more importantly, drug product performance cannot be properly assessed.

QbD for excipients not compulsory, but recommended

There are no specific regulatory requirements for excipients relating to QbD, and QbD is not compulsory in the United States. QbD guidelines for drug product development have been documented by the International Council for Harmonisation (ICH) and only include excipients in as much as excipients are a part of the drug product composition, notes Zeleznik. However, that does not change the fact that excipient variability will be important for all users to understand who may want to submit a QbD-related drug application, according to Schoneker.

QbD is a science-based approach that is complementary to traditional regulatory compliance approaches, says Carlin. Compliance does not ensure fitness for purpose in a finished product: additional product-specific specifications may be required, most notably critical material attributes (CMAs). “It is good practice to understand excipient variability and its impact on drug product performance to minimize any impact to patient safety and/or drug product efficacy,” he comments.

Moreton adds that excipients intended for human use, either in clinical trials or after commercial launch, should be manufactured to appropriate good manufacturing practice (GMP) standards per the United States Pharmacopeia (USP)–National Formulary (NF) General Notices (even if they do not have a USP or NF monograph) or another pharmacopeia depending on the jurisdiction. For topical products, Karry notes that using GMP-grade raw materials is not a requirement, and many companies use cosmetic-grade raw materials because they are less expensive, which has other consequences from a supplier accessibility and regulatory perspective.

Annual product quality reviews (APRs) may also be valuable for addressing the needs of QbD programs at drug manufacturers, Karry comments. BASF performs APRs to verify that its processes remain in a validated state and assess if there are systematic process or quality defects. The data-trending component of APRs helps the excipient supplier work with the drug product formulator to analyze the distribution of certificate of analysis (CoA) parameters, information she says can potentially be used to expand the design space and make it less susceptible to intrinsic material and process variability, thereby increasing robustness.

Data, communication, lack of understanding, and other challenges

The challenges to incorporating excipients into QbD programs are numerous and diverse. Communication can be a major hurdle to incorporating excipients into QbD programs, according to Zeleznik. “Drug product manufacturers may not fully understand or appreciate excipient composition complexity and/or variability as well as the potential impact to drug product performance. It is important that pharmaceutical product manufacturers have open dialogue with excipient suppliers regarding excipient choice and application in a drug product. Relying on ingredient specifications and monograph requirements and CoA data is often not enough.Asking whether there [are] any data or information related to a particular application very well could help with product development and consistent drug product manufacture and, more importantly, performance,” he remarks.

Karry points to a lack of sufficient historical data to understand the impact of intrinsic excipient variability throughout its retest period on drug product safety and efficacy. She also notes that many drug manufacturers, rather than work with excipient manufacturers to jointly evaluate the data and understand risks, resort to adding more variables to their design of experiment (DoE) studies. “It is a common misconception that a QbD approach to pharmaceutical development will always result in more experiments and test batches,” she observes.

In a similar vein, Zeleznik observes that there is a misconception regarding “QbD samples,” which in fact don’t exist, at least, he says, not in the way that pharmaceutical companies desire—“manufactured at the edge of specification.” “This ill-conceived notion that excipient manufacturers can or would be willing to manufacture to edge of specification is impractical.There are too many interdependencies among some acceptance criteria making it impossible as well as the number of permutations that would need to be created,” he states.The more practical approach, Zeleznik says, is to secure samples that are at the boundaries within normal variation, if available.

For Moreton, the fact that most excipients are produced in large volume using continuous manufacturing is a challenge to providing samples at extremes of specification. “These processes operate in a form of balanced equilibrium and changing one processing parameter may mean that another parameter has to be changed to compensate. In some cases, it may not be possible to make the change. The result is most often that the production of excipients with properties at the limits of specification cannot be achieved,” he explains. He adds that the IPEC-Americas QbD Sampling Guide for Excipient Makers, Users, and Distributors (2016) was developed to explain ways in which it may be possible to simulate excipients at the limits of specification.

Other challenges noted by Carlin include:

overreliance on pharmacopeial and supplier specifications for excipients without identifying product-specific requirements, which does require more investment during development but minimizes lifecycle quality and supply chain security costs

failure to distinguish attribute types, including those without acceptance criteria, such as performance-related properties (PRPs)/functionality-related characteristics (FRCs), and critical material attributes (CMAs)

extensive use of outsourcing and decreasing vertical integration in drug product manufacturing, which inhibits the ability to conduct the in-depth assessments that are needed to factor in the impact of excipients.

Asking questions, using model compounds, and pursuing DoE studies

The growing recognition of the value of the QbD approach and the need to thoroughly understand all aspects of a manufacturing process are leading to the development of solutions for many of these challenges. “Pharmaceutical companies are starting to ask more questions about excipients.This is a significant step towards overcoming challenges related to product development and the impact associated with excipients,” Zeleznik notes.

For instance, Karry observes that some drug companies are working with excipient manufacturers to “open the books,” enabling joint evaluation of relevant data and exploration of the potential impacts of variability in both CoA and non-specified parameters. As an example, she points to a recent project in which BASF worked with a customer that was using fine crospovidone for its binding disintegrant functionality.

It was found in this joint project that large changes in particle-size distribution (PSD) affected tablet hardness and friability. While particle-size distribution (PSD) is not a monograph specification, it is an FRC that depends on the excipient use. It is not included in the crospovidone CoA, but BASF measures it internally. Analysis of historical data on the variability of crospovidone PSD revealed low variability. BASF also conducted a quick study in the compaction simulator using a crospovidone lot with higher PSD values to confirm the assessment that the material was low risk. “This is one example of how drug manufacturers, working with the excipient producers, can expedite and de-risk drug development,” Karry believes.

Other practices that help to overcome challenges associated with incorporated excipients into QbD programs are the adoption of a model compound approach, the use of methods outlined in the IPEC QbD Sampling Guide, and leveraging statistically driven DoE studies to get maximum benefit from a minimum number of experiments, according to Moreton.

DoE studies, according to Zeleznik, can help drug manufacturers understand the impact of variability in drug substances, excipients, and manufacturing processes on drug-product performance. A full-factorial design, adds Moreton, can be very inefficient and wasteful of materials, time, and resources. There are other better designs that can be statistically analyzed to provide clearer results and conclusions using fewer experiments.

Excipient suppliers have an important role to play

QbD is not a new concept. The principles have been used by the semiconductor and microelectronics industries for decades, Zeleznik observes. There have been many names by which the principles have been known; however, the principles have changed little from one naming convention to another.

The fine chemicals industry, of which excipients are a part, has also been using these same principles for decades, Zeleznik says.“The heart of the concept is understanding those parameters that impact product quality such as process and raw material fluctuations and designing a robust process that minimizes finished-product variation, ensuring lot-to-lot consistency,” he states. In essence, Zeleznik concludes, the excipients industry predates the pharmaceutical industry by many years in “QbD” use.

Moreton agrees that excipient manufacturers using continuous manufacturing have probably already undertaken something analogous to QbD to develop their manufacturing process(es), although it would not have been called QbD. “Once the excipient and process have been developed and the excipient launched into the market place, then statistical process control methods would be used to ensure that the excipient continues to meet the manufacturer’s specification,” he comments.

The high degree of process and material understanding that comes with statistical process control enables high-volume continuous manufacturing, which provides cost-effective availability of high-quality common excipients, adds the IPEC-Americas panel. “Raw materials and processes will vary from supplier to supplier, however, and are subject to the demand and economics of the major markets. In addition, reliance on pharmacopeial compliance may hide changes by a supplier or differences between suppliers and change control is ineffective against force majeure when pharmaceutical consumption is relatively small,” the group believes.

Despite these issues, excipient suppliers can play a very important role in increasing formulation knowledge and experience, adds Karry. “Wider design spaces can be created by thorough evaluation of historical data and with selected raw material lots that offer flexibility in drug development to accelerate scale-up and establish appropriate control strategies for commercial manufacturing,” she notes.

Providing advice on which parameters may be useful in which applications (formulations) is another way in which excipient suppliers can help drug developers with their QbD initiatives, particularly if manufacturers provide information on the impact of excipient manufacturing variability raw material/feedstock seasonal variations, etc.

“Excipient suppliers may be able to supply excipient samples and information pertaining to excipient variability (including both physical properties and composition), but only if they understand what the drug product developer is trying to achieve,” agrees the IPEC-Americas panel. That again requires two-way communication between excipient suppliers and drug-product developers.

The COVID-19 pandemic has impacted supply chains across all industries. Pharmaceutical and excipient manufacturers have not been excluded. Drug-product developers with robust products and effective risk-management and multi-sourcing strategies (i.e., QbD) most likely fared better, according to the IPEC-Americas panel.

“Drug manufacturers that have implemented QbD are battling supply challenges, but their upper hand is at the time of qualifying new vendors (excipient manufacturers). A risk assessment that lists and ranks CMAs and their impact on drug-product critical quality attributes is an essential part of a QbD application. With this documented knowledge on the impact of excipient and API variability, procurement and technical service departments can work together to accelerate material evaluation and new vendor qualification, thus minimizing disruptions,” Karry explains.

Those drug makers that implemented a QbD approach during product development that included the identification of multiple ingredient sources as part of the development program have fared better, according to Zeleznik. “This fact is truly a measurement of the positive impact QbD can have. Knowing how changing excipient suppliers (when feasible) can potentially impact drug product quality and performance during product development greatly minimizes risk during supply chain disruptions,” he concludes.

Incorporation of Pharmaceutical Excipients into Product Development Using Quality-by-Design (QbD Guide)

 (1) was issued at the end of 2020 to complement the 

IPEC-Americas QbD Sampling Guide for Pharmaceutical Excipient Makers, Users, and Distributors 

(2), which was published in 2016. The guide, notes Karry, informs on user/regulatory expectations when incorporating excipient variability into formulation development and why to look past specifications. There is a lot of useful information for both excipient suppliers and users, according to Moreton.

One of the key messages in both of the IPEC guides and expressed repeatedly by industry experts is that communication is critical if QbD is to work as intended.This key takeaway applies to both drug-product developers and excipient manufacturers. “Drug-product manufacturers must be willing to share how an excipient will be used so that excipient suppliers can provide pertinent information that could
help understand the excipient’s impact on formulation performance,” Moreton emphasizes.

1. IPEC Federation, “New IPEC Guide: Incorporation of Pharmaceutical Excipients into Product Development using Quality-by-Design,” Press Release, November 30, 2020.
2. IPEC-Americas, “IPEC-Americas Publishes Quality by Design Sampling Guide for Excipient Makers, Users, and Distributors,” Press Release, May 2, 2016.


Volume 46, Number 4
April 2022
Pages: 23–26

When referring to this article, please cite it as C. Challener, “Bringing Excipients into the Quality-by-Design Paradigm,” 

Although not easy to do, it is essential because excipients can affect drug-product safety and efficacy.

Bringing Excipients into the Quality-by-Design Paradigm

Treatment of bacterial infections with bacteriophages (phages)—viruses that enter bacterial cells and rapidly multiply, quickly rupturing the cells and destroying the bacteria—has been known to be effective since the early 1920s. The advent of broad-spectrum antibiotics led to a halt in phage therapy research, however, except in Eastern Europe, particularly Georgia, and to some extent France (1).

Bacteria, meanwhile, have developed resistance to many antibiotics, and new “superbugs” that cannot be treated with even the most powerful antibiotics are increasingly common. There is real potential that the world could enter a post-antibiotic era in which giving birth or getting a simple
cut could present a serious risk of death. The situation is exacerbated by the fact that antibiotics have long since been commoditized, and most major pharmaceutical companies halted their antibiotic development programs in favor of investments in more lucrative areas such as oncology. Few new antibiotics drugs have been approved as a result.

Consequently, the need for alternatives to traditional antibiotics has become urgent. In addition to leading to the development of novel chemical approaches, the current threat of antimicrobial resistance is driving renewed interest in phage therapy. A lack of appropriate infrastructure and specific regulatory framework are two main challenges to the realization of marketed products. Fortunately, developers of phage-based treatments expect these hurdles to be surmountable in the medium term, with several candidates in or soon to enter clinical trials.

Fighting bacteria that are resistant to current antibiotics is what most people see as the main driver of interest in the development of phage-based therapies. For Alexander “Sandro” Sulakvelidze, president and CEO of bacteriophage developer Intralytix, there is another important factor: growing understanding of the human microbiome and its role in health and disease.

“The microbiome field is exploding, with a lot of bright minds working in the area. People are establishing links between microbiome composition and diseases ranging from those having obvious bacterial etiology (e.g., infectious and gastrointestinal diseases like bacterial dysentery) to disorders that are not typically associated with bacterial infections, such as obesity, cancer, and others,” Sulakvelidze explains. “That means that with bacteriophages we not only have the potential to manage drug-resistant infections, but also a tool that may be able to beneficially modulate the microbiome to address both infectious and noninfectious diseases,” he states.

Indeed, the human microbiome comprises hundreds of bacterial species, and maintaining the right balance of “good” and “bad” bacteria in the gut microbiome helps maintain health through multiple mechanisms including modulation of inflammation and regulation of protective gastrointestinal functions, according to Sulakvelidze. “Lytic bacteriophages are superbly suited for gentle and targeted fine-tuning of the microbiome by killing their specific targeted bacterial pathogens without disturbing the normal microflora—a unique biological property that is increasingly explored for developing novel tools for microbiome modulation and research,” he observes.

While broad-spectrum antibiotics are attractive because they can be used to treat a wide range of bacterial infections, they also do not discriminate between “good” and “bad” bacteria. Dysbiosis and secondary infections (e.g., fungal infections, inflammatory bowel disease, reactive arthritis, etc.) can occur as a result, complications that have not been observed with phages (1). Phages could also be beneficial for patients with allergies to the commonly used penicillins, sulfonamides, and tetracyclines.

At the simplistic level, notes Sulakvelidze, phages infect bacteria by first attaching to their cell membranes. They then inject DNA into the host cells. Within 60 seconds, the phage DNA takes over and shuts down the cellular machinery of the bacteria, which allows for phage DNA replication. Within 20–40 minutes, approximately 40–200 bacteriophages exist in each of the bacterial cells, causing the cells to burst. The bacteria die, and the phages are released to seek out and infect additional targets.

This mechanism of action is different from that of traditional antibiotics. As a result, while bacteria can become resistant to phages, the mechanisms involved are very different from the one against antibiotics. “The resistance that bacteria develop to antibiotics does not affect their resistance to phages, making these two approaches complementary,” Sulakvelidze observes. Indeed, often phages can be effective against bacteria that have developed resistance to antibiotics. There have been several case reports of the effective emergency treatment of patients for which conventional antibiotics have failed (1).

The specificity of phages is advantageous because it does not result in the death of desirable bacteria. It is, however, one of the reasons that phages fell out of favor after the introduction of antibiotics. For phage therapy to be effective, it is necessary to know which bacterium is causing the infection, which is not the case for broad-spectrum antibiotics, according to Sulakvelidze. It can take time to identify the specific phage or cocktail of phages that will be effective, time that some patients may not have, particularly in cases where phages are used as a treatment of last resort (1).

Antibiotics creating problem and inhibiting alternative solutions

Another difficulty facing the advance of phage-based therapies is the fact that the medical infrastructure that exists for the treatment of bacterial infections in most of the world has been designed around antibiotics (2). From susceptibility testing kits to the sophisticated machinery required for high-throughput testing and the training of hospital and clinical personnel, everything is geared toward antibiotics, Sulakvelidze comments.

“The business model for phages is very different from that for antibiotics, which creates a whole range of challenges from manufacturing and distribution to diagnosis and identification of the right phage treatment for each patient,” says Sulakvelidze.

For Grégory Resch, head of the laboratory of bacteriophages at the Center for Research and Innovation in Clinical Pharmaceutical Sciences at Lausanne University Hospital, Switzerland, one of the biggest challenges is the complexity around producing many different specific phages under good manufacturing practice (GMP) conditions, which contrasts with the existing access to broad-spectrum antibiotics. He also notes that patenting phages is not as obvious, because many of them can easily be isolated from the environment.

Phages are manufactured via fermentation using the bacteria that serve as the natural host of the phage in question. The phage reproduces, killing the bacteria. The phage must then be separated from the dead bacteria and purified, as the dead bacteria and other contaminants can cause undesired immune responses. Fortunately, advances in fermentation technology and downstream processing have enabled successful, large-scale production of high-quality phage-based products, according to Sulakvelidze.

Production challenges, although they are being addressed, are further complicated by a lack of an established regulatory framework for the approval of phage-based therapies. The absence of a clear definition for bacteriophages, common and validated dosage protocols, and the length of phage treatments, for instance, creates uncertainty with respect to the development of clinical programs (2). On the positive side, however, many of the disadvantages of phage-based therapy relate to infrastructure and knowledge gaps that can be resolved as the field progresses.

Even so, Sulakvelidze comments that the advances Intralytix and other bacteriophage developers, such as Adaptive Phage Therapeutics and Armata Pharmaceuticals, have made have taken longer than he anticipated. “Even with the many years of work and growing number of companies involved in the field, it will still be many years before phage-based therapy becomes a mainstream treatment or at least somewhat commonly used,” he contends.

Intralytix was formed in 1998 by Sulakvelidze and his post-doctoral advisor Glenn Morris, an infectious disease specialist who had a patient die after a sophisticated surgical procedure due to a drug-resistant infection of the intestine—and who was not familiar with phage-based therapy. The initial goal of the company, says Sulakvelidze, was to develop phages to treat infections caused by vancomycin-resistant bacteria called enterococci or VRE. It became quickly apparent to the founders that the time was not right for targeting clinical applications given the long list of challenges for human medical applications.

Instead, Intralytix shifted its focus to food safety, which has given the company time to establish greater knowledge, build a manufacturing facility and develop effective production processes, work with regulators, and establish some of the infrastructure needed to support phage-based products. Its first commercial product was ListShield, an all-natural, non-chemical antimicrobial preparation for controlling the foodborne bacterial pathogen Listeria monocytogenes.

Today, Intralytix is using the sales revenues from its portfolio of phage-based food protection products to support the development of nutraceuticals and drug candidates. The company will launch its first dietary supplement/probiotic pill to enhance natural gut resistance against certain pathogenic bacteria in March 2022, with a second to be introduced in 2023.

Some phage-based companies focused on the development of drug candidates are also leveraging advanced genome sequencing and metagenomics technologies to engineer genetically modified phages with improved patentability, according to Resch. He adds that the hope is that these advanced phages will also have enhanced activity without impairing safety, but sufficient evidence of this benefit has yet to be gathered.

Academic centers and government bodies are also getting involved in the field of phage-based therapies, helping startup companies with funding and other means of support. One example highlighted by Resch is IPATH, the Center for Innovative Phage Applications and Therapeutics, which is located at the University of California, San Diego School of Medicine and the first dedicated phage therapy center in North America.

Over the past one hundred-plus years, phages have been administered to humans orally (tablets and liquids), rectally, topically (skin, eye, ear, etc.) as rinses and creams, intravenously, and via other
delivery approaches.

Today, phage-based therapies are in preclinical development for the treatment of a wide variety of diseases, including lung, wound and gut infections, as well as endocarditis and many other diseases that are difficult-to-treat because of the potential for complications due to antibiotic resistance.

When it comes to clinical trials, only a few have been conducted and/or are ongoing in Western medicine, according to Sulakvelidze. Phase I and Phase II studies involving phage-based therapies have been completed in chronic otitis media, respiratory infections, infected burn wounds, gastrointestinal disorders, urinary tract infections, and venous leg ulcers (1). The most common targets, says Sulakvelidze, are gastrointestinal and wound/skin infections.

One of Intralytix’s prototype phage preparations for treating infected wounds was successfully used during a Phase I human clinical trial in Lubbock, Texas—the first Phase I trial in wound healing in the United States. The company’s EcoActive bacteriophage therapy targeting adherent-invasive Escherichia coli(AIEC) in Crohn’s disease patients entered a Phase I/IIa clinical trial in 2019 and is currently enrolling participants at the Icahn School of Medicine at the Mount Sinai Hospital in New York, NY.

In October 2021, Intralytix received clearance from FDA for an investigational new drug (IND) application for ShigActive, a bacteriophage preparation to manage Shigella infections in humans, of which there are approximately 125 million cases and 14,000 deaths worldwide, the majority of the latter in children under the age of five. The company is also in the pre-IND stage with a candidate to treat VRE infections. Altogether, Sulakvelidze says Intralytix will be starting three additional clinical trials in the next 18 to 24 months.

The increasing number of developmental drug products and clinical trials is a hopeful sign for the future of phage-based therapy and a first step in advancing the field. During the next few years, Sulakvelidze expects to see even more clinical trials and greater numbers of people involved in generating an ever-broadening base of scientific knowledge and establishing the infrastructure needed to enable a phage-based approach to the treatment of disease.

“Eventually,” Sulakvelidze remarks, “there will be more reference centers and clinics—maybe a handful—where people can go to get treated with bacteriophages by properly trained experts with access to the right equipment. When enough centers are established, phage-based therapy will become more commonplace nationwide, but progress toward that goal will be incremental.”

Resch adds that greater capacity to produce phages under GMP conditions will need to be constructed to support the products that advance to late-stage clinical trials and commercialization.

Part of Sulakvelidze’s reason for having high expectations for bacteriophages in medical applications is the experience Intralytix has had with FDA regarding its food safety products. “The first product took four years to get approved, with a lot of back-and-forth between the company and FDA that largely involved educating one another. The agency has required considerably less time (9 to 12 months) to reach decisions on subsequent products,” he observes.

Sulakvelidze expects that experience to translate to the company’s human health products. “FDA’s Center for Biologic Evaluation and Research is very much open and willing to work with companies developing phage-based therapies to establish a regulatory framework for ascertaining their safety and effectiveness,” he comments.

“With the potential for bacteriophages when used in combination with antibiotics as first-line therapies to provide personalized treatment solutions for challenging patient infections, there is the real [opportunity] for this new approach to be democratizing,” insists Resch. That potential in conjunction with the urgent need for solutions to the rapidly growing threat of antibiotic resistance point to a bright future for phage-based therapies.

1. J-P Pirnay, T. Ferry, and G. Resch, “Recent Progress Toward the Implementation of Phage Therapy in Western Medicine,” 

Cynthia A. Challener, PhD, is a contributing editor for 


Vol. 46, No. 3 
March 2022 
Pages: 21–23

When referring to this article, please cite it as C. Challener, “The State of Phage Therapy,” 

Bacteriophages could be crucial weapons in the fight against antibiotic-resistant bacteria.

The State of Phage Therapy 

The success of the messenger RNA (mRNA) vaccines against the SARS-CoV-2 virus brought attention to a field that has steadily advanced for many years. Investment in this space has ramped up dramatically, and many applications of mRNA technology are rapidly advancing through pre-clinical development as well as clinical trials.

As with all drug or vaccine candidates, proposed mRNA products must meet regulatory requirements for analytical characterization as outlined by the International Conference on Harmonisation (ICH), the World Health Organization (WHO), FDA, the European Medicines Agency (EMA), and other health authorities around the globe.

Unlike most other drug substances, mRNA must be formulated within specialized nanoparticles, most commonly consisting of lipids, both to protect it from degradation and to facilitate its transit across cell membranes. Additional analytics are therefore required to ensure the quality and safety of the nanoparticle formulation as well as the mRNA molecule itself.

A key activity in the early development phase of mRNA therapeutics is extensive characterization of mRNA and nanoparticle quality attributes as these are known to strongly influence biological efficacy. Given the shrinking timelines for drug development, access to faster and higher-throughput analytical methods has become vital. Indeed, it is essential that analytical approaches for use during mRNA product development and quality-control (QC) testing must keep pace to ensure the identity, safety, and efficacy of these new prophylactic and therapeutic modalities.

Although analytical requirements for mRNA candidates are more complex than those for traditional biologics, some testing needs are similar while others are quite different. “There is a common need to adequately characterize both protein therapeutics and mRNA therapeutics to confidently identify and quantify any quality attributes that will impact their efficacy and safety,” says Todd Stawicki, global marketing manager, mass spectrometry, for the biopharmaceutical industry at SCIEX. He points to the need to identify process-related impurities—host-cell proteins (HCPs) in the case of protein therapeutics and a variety of genetic impurities like truncated transcripts or incorrect DNA template in the case of mRNA.

The differences are notable, however. Rather than focusing on post-translational modifications as is the case for protein therapeutics, there is a lot of emphasis on characterization of mRNA, the delivery systems, and cellular uptake at the discovery phase of drug development, because unlike engineered proteins and monoclonal antibodies (mAbs) that are ready to start functioning upon delivery, mRNA once delivered to cells provides instructions for producing the proteins that do the work, according to Brian Liau, a solution development scientist at Agilent Technologies, Singapore.

Manufacturing for mRNA products, furthermore, requires unique process steps such as in vitro transcription (IVT) and lipid nanoparticle formulation, which naturally creates different analytical needs, adds Ryan Hanko, manager of quality control for Catalent. IVT is a chemical rather than a cell-based process, expounds Joe Fredette, senior business development manager of biopharmaceuticals at Waters. It also involves the use of an enzyme called an RNA polymerase that transcribes DNA into mRNA.

As an example of different analytical needs, Hanko notes that mRNA products require QC assays to be developed that measure residual enzyme (such as polymerase or endonuclease), which may be present after the IVT step, to ensure that it is not present in the final product. Confirmation of the RNA sequence and determination of the efficiency of capping at the 5’ end and poly(A) tail distribution at the 3’ end are also unique to mRNA, notes Ashleigh Wake, business development director for Intertek Pharmaceutical Services. The potential impurity profile is also quite different to other molecules, and methods to quantify any residual plasmid or double-stranded RNA are also required.

In addition, lipid analysis workflows are necessary for characterization and chemistry, manufacturing, and controls (CMC) testing of mRNA products, including liquid nanoparticle (LNP) composition analysis to ensure the right mix ratio of lipids within the formulation, lipid ID confirmation, and impurities analysis and screening, according to Fredette.

In essence, summarizes Wake, there is a similarity in the overall requirements for product characterization in that the intent is to assess or confirm identity, purity/impurities, stability, activity, etc. “However,” she underscores, “to fully accomplish this, there is a need to include mRNA-specific analytics that allow assessment of these attributes.”

Evolving analytical needs from early to late-phase development

Another important difference between the development of protein- and mRNA-based products is the analytical burden during the early discovery phase. As traditional drug development typically involves mAbs, says Dr. Liau, bioanalytical requirements tend to be relatively modest because even sub-optimal molecules may be used to demonstrate target engagement and a therapeutic effect. In contrast, mRNA products require several biological processes, including cellular uptake, endosomal escape, and protein translation to take place efficiently before any effect may be observed. Hence, analytical characterization of mRNA and delivery vehicle quality attributes are important from the outset.

“For process scale-up and GMP [good manufacturing practice] manufacturing/product release, chemical characterization of mRNA remain important. However, the focus tends to shift towards ensuring consistent size polydispersity and mRNA encapsulation in the formulated product, as well as identifying process-related impurities,” Dr. Liau comments.

With mRNA candidates, Stawicki adds that scale up of the enzymatic process requires significant and difficult scale up for all upstream raw materials—nucleoside triphosphate (NTPs), enzymes, capping reagents, cofactors, and multiple classes of lipids. “The majority of these components are large, complicated biomolecules with their own associated scale up, purification, and analytical challenges,” he explains.

There are also some differences in the attributes that are monitored during production, according to Hanko. A260 concentration checks and osmolality testing are the primary monitoring assays in early development and process scaleup for in-process observations, while during GMP manufacture RNase testing is important to ensure the final product will not be compromised by incidental contamination from non-product materials.

Core release tests include identity determinations, final concentration, impurity content (e.g., residual protein, dsRNA, rDNA), capping efficiency, and poly-A tail, in addition to typical compendial evaluations for safety and quality attributes.

There is an extensive list of critical quality attributes (CQAs) that must be monitored to meet regulatory requirements regarding the assessment of the identity, functionality, and safety of mRNA therapeutic/vaccine products (see 

). “Confirmation that the specific mRNA sequence has been generated, that the mRNA solution is at target pH, and that any potential process impurities (solvent, protein, DNA-related) have been controlled will be required,” says Matthew Howard, a senior specialist in quality assurance at Catalent.

Table I. Key critical quality attributes (CQAs) that must be monitored for

messenger RNA (mRNA) therapeutic/vaccine products.

Assurance will also be needed that the translation-promoting and
degradation-preventing characteristics of the 5’ cap and poly-A tail are sufficient, says Howard. The efficiency of capping at the 5’ end can influence both target protein production and overall immunogenicity, while the length/distribution of the poly(A) tail is critical for translation and overall protection of the mRNA, Wake explains.

Adds Maxwell Meller, senior scientist, quality control, with Catalent: “The 5’-capping of the mRNA molecule is critical to its integrity upon delivery to the target site and is a unique requirement for mRNA production compared to other kinds of drugs. Characterization and monitoring of capped material, however, have proven to be time- and resource-intensive.”

For the lipid components, confirmation of the identity of each lipid in the LNP mix and that they are present in the correct ratio is essential as these CQAs can directly impact LNP formation and efficacy, according to Fredette. It is also important, he emphasizes, to ensure that lipid impurities are well controlled for and below critical thresholds, as both lipid and mRNA impurities can adversely impact process outcomes and in some cases lower the potency of the mRNA.

The sensitivity of mRNA to degradation by enzymes, particularly RNase, creates additional unique requirements when working with mRNA-based therapeutics and vaccines. For instance, Hanko observes that the use of RNase-eliminating preparations is vital and laboratories should consider physical space segregation in addition to personnel training and awareness regarding the maintenance of RNAse-free zones, equipment, and personal protective equipment (PPE).

These actions are important, Hanko says, because a compromised mRNA sample will show lower-than-expected purity in those assays. Some analyses, as those for residual impurities, are arguably not impacted by compromised mRNA and others may only require heightened RNase sensitivity depending on solution preparations and material manipulations. “Even so,” Hanko states, “the core method performance expectations must be understood for all methods regardless of the level of mitigation required.”

Analytical approaches must keep pace to ensure the identity, safety, and efficacy of evolving mRNA candidates.