David Schoneker is president, Black Diamond Regulatory Consulting, LLC

David Schoneker

Excipients and Intended Use

 spoke with David Schoneker, president, Black Diamond Regulatory Consulting about what goes into the development of a new and/or novel excipient. In part 3 of this series, Schoneker emphasizes that excipient manufacturers must balance market expansion with the significant data requirements and liabilities associated with different routes of administration.

New excipients are typically created with a specific target market and intended use in mind—often starting with oral applications to manage the volume of required safety and analytical data.An excipient is utilized for an application outside of this intended scope, such as moving from oral to parenteral delivery, may pose challenges.The supplier may lack the necessary safety data to support the new application or may even refuse to sell the material due to liability concerns.

Schoneker highlights that the decision to develop additional data is often an economic one; the high cost of toxicity studies must be justified by the expected sales volume. This creates a gap where pharmaceutical companies may find that no existing excipient solves a specific formulation hurdle. To bridge this gap, Schoneker advocates for collaborative negotiations. When a drug developer has a critical need for a novel excipient, they may choose to co-fund or fully sponsor the required toxicity studies.

These collaborations frequently involve exclusivity agreements, allowing the drug developer a period of sole access to the technology before the manufacturer expands the market to establish a broader regulatory precedent. Early engagement with suppliers may ensure that the available safety data aligns with the drug’s clinical objectives.

Watch the interview above to learn more about what goes into the development of a new excipient. Dave will be participating in the workshop, “Risk Based Framework for Development of New Excipient Products”, at 

 being held in Nashville from May 4-6, 2026.

Raghuram M, Sheehan C, Filler R, Schoneker D, Liu J, Gronewold C. Risk Based Framework for Development of New Excipient Products and USP’s Novel Excipient Emerging Standards Approach to Meet Stakeholder Needs. Presentation at Excipient World Conference & Expo 2026. May 4, 2026. 

https://s6.goeshow.com/ipec/annual/2026/conference_program_sessions.cfm?session_key=B7748D16-9EBD-188A-D5EE-3FF177ECEAC0&session_date=Monday,%20May%2004,%202026

Videos

In part 3 of a multi-part series, David Schoneker, president, Black Diamond Regulatory Consulting, talks about the collaboration between the pharma company and the excipient supplier when different routes of administration are considered for an ingredient.

Regulatory Involvement in Excipient Development

 spoke with David Schoneker, president, Black Diamond Regulatory Consulting about what goes into the development of a new and/or novel excipient. In part 2 of this series, Schoneker talks about the distinction between market volume and technical necessity: while more new excipient products target small-molecule drugs due to their market prevalence, large-molecule therapeutics may require truly novel excipients to achieve commercial viability. These innovations are often the result of collaborative development between excipient manufacturers and pharmaceutical companies aimed at solving specific formulation challenges, improving productivity, or reducing costs.

In part 1 of a multi-part series, David Schoneker, president, Black Diamond Regulatory Consulting, explains the difference between a new excipient and a novel excipient and what goes into developing a new excipient. 

From a regulatory perspective, Schoneker clarifies that regulatory bodies like the FDA are generally not involved in the development process unless there is a significant public health imperative, such as the development of lipid nanoparticles for COVID-19 vaccines or the transition to environmentally friendly inhaler propellants. According to Schoneker,the FDA does not approve excipients in isolation. Unlike the petition process for food additives, pharmaceutical excipients are only evaluated and authorized as part of a specific drug product application. Therefore, the Inactive Ingredient Database (IID)

 should not be interpreted as a list of approved substances. Instead, it serves as a precedent-of-use reference, indicating levels and routes of administration that have been previously accepted in approved drug products.

While utilizing an excipient within these established precedents usually facilitates a smoother review, the FDA maintains the authority to require justification for any excipient's use in a new drug context. Understanding this distinction may help pharma companies navigate the path from formulation development to regulatory submission.

FDA. Inactive Ingredients in Approved Drug Products Search: Frequently Asked Questions. 

. January 26, 2022. Accessed April 29, 2026. 

https://www.fda.gov/drugs/drug-approvals-and-databases/inactive-ingredients-approved-drug-products-search-frequently-asked-questions

FDA. Inactive Ingredients Database Download.

. April 13, 2026. Accessed April 29, 2026. 

https://www.fda.gov/drugs/drug-approvals-and-databases/inactive-ingredients-database-download

In part 2 of a multi-part series, David Schoneker, president, Black Diamond Regulatory Consulting, explains what drives the need for the development of a new excipient and how involved regulators are in the process.

New Excipient Development–Part 1

The term “new excipient” can refer to different product types, according to David Schoneker, president, Black Diamond Regulatory Consulting. Excipient innovations include new chemical entities (NCEs), products designed for higher levels of use, new routes of administration, or specific new patient populations. They also encompass new grades of existing excipients, pre-mixed or co-processed materials, and slight chemical modifications. In some cases, substances are adapted from alternate industries, such as foods and cosmetics, to serve pharmaceutical functions.

Adoption of new excipients by formulators is often a slow process. The development of actual novel NCE excipients is particularly rare, primarily due to the prohibitive amountof safety data required for approval. Furthermore, the pharmaceutical industry typically exhibits a lack of acceptance for these novel materials unless they provide a solution to a problem that no other existing substance can address.

In terms of application, small-molecule drugs currently drive the majority of new excipient development due to the magnitude of potential uptake in the market, according to Schoneker. However, the commercialization of large molecules may occasionally depend on the creation of a truly novel excipient, often resulting in collaborative development between excipient manufacturers and pharmaceutical companies.

Ultimately, the push for these new products is driven the need to fulfill an unmet need within a pharmaceutical company or a desire by an excipient manufacturer to expand their market. By creating new products, these companies aim to compete more effectively with existing excipients currently on the market.

Watch the interview above to learn more about what goes into the development of a new excipient. Dave will be participating in the workshop, “Risk Based Framework for Development of New Excipient Products”, at 

 being held in Nashville from May 4-6, 2026.

In part 1 of a multi-part series, David Schoneker, president, Black Diamond Regulatory Consulting, explains the difference between a new excipient and a novel excipient and what goes into developing a new excipient.

Microcrystalline cellulose, refined wood pulp, texturizer, anti-caking agent, fat substitute, emulsifier, used in vitamin supplements or pills. | Image Credit: ©RHJ - stock.adobe.com

The International Pharmaceutical Excipients Council (IPEC) defines a co-processed excipient as a combination of 2 or more compendial or non-compendial excipients designed to physically modify their properties in a manner not achievable by simple physical mixing, and without significant chemical change.

In some instances, formation of necessary components may occur, such as in situ salt formation.

In modern pharmaceutical formulations, co-processed excipients (CPEs) enable drug product manufacturability, stability, and performance that are not achieved when the CPE components are used individually in a simple blend. With the increased functional performance, formulators are turning to CPEs, which are engineered combinations of 2 or more excipient components integrated at the particle level (

Figure 1. "Simple" microcrystalline cellulose/fumed silicon dioxide blend (top right) compared to the co-processed silicified microcrystalline cellulose (bottom right).In co-processing, fumed silicon dioxide is added to microcrystalline cellulose slurry before drying creating an integrated system. Figure courtesy of the authors.

With the demonstrated benefits of CPEs in batch processing, it was a natural progression to their use in continuous manufacturing, which enables higher throughput and patient-centric dosage forms. Understanding the nature, benefits, and regulatory implications of CPEs is becoming indispensable for product formulators and supply chain decision-makers.

Historical Context and Current Prevalence of CPEs

The idea of co-processing is not new. The pharmaceutical industry has long used co-processed excipients. Classic examples include sugar spheres (sucrose and corn starch) for multiparticulate systems and the CPE combination of carboxymethylcellulose sodium (NaCMC) and microcrystalline cellulose (MCC) grades developed to improve liquid delivery. Other widely used cellulose combinations such as MCC and lactose; lactose and powdered cellulose; and silicified microcrystalline celluloses (SMCC) are examples where combining functional materials has produced practical benefits for decades. Today, more than 100 co-processed excipients exist, many of which are reported to be in commercial use, spanning direct-compression excipients, multifunctional binders, disintegrant-binder combinations, and specialty performance excipients, such as those used for orally disintegrating tablets (ODTs). Several of the co-processed materials identified above have achieved compendial recognition within the United States Pharmacopeia (USP). The growing number of CPEs reflects both historical safety experience and the practical manufacturing advantages they offer.

It is important to recognize that the individual components used in the manufacture of many CPEs are not isolated as single, compendial excipients prior to co-processing; however, they are carefully controlled. CPE manufacturers may employ different approaches to co-processing depending on the manufacturing processes used, components comprising the CPE, and the targeted physical and functional characteristics. In principle, there are 3 manufacturing pathways to produce CPEs. Each pathway yields an excipient whose composition is designed to work synergistically without significant chemical change to the components.

In practice, co-processing can be accomplished by several manufacturing routes:

Use of commercial excipients: Finished excipients are combined and subjected to a process (eg, milling, granulation, spray drying, or agglomeration) that integrates the components into particles comprising those materials (

A commercial excipient is introduced and combined with an in-process excipient that has not yet been isolated (eg, a polymer solution or slurry), and the combined stream is processed to integrate the components into particles comprising those components (eg, spray drying) (

All CPE components are in-process excipient streams coming together for co-processing: 2 or more material streams (eg, polymer dispersions, microcrystalline cellulose slurries, sugar-based solutions) are combined, mixed, and processed into particles without isolating any of the individual components first (

Figure 2. Commercial or finished excipients used to manufacture co-processed excipient. Figure courtesy of the authors. 

These manufacturing pathways affect physical characteristics, including particle morphology (particle shape and porosity), surface properties, particle size and size distribution, and moisture level, which in turn influence performance properties such as powder flow, compressibility, and robustness in the case of tablet manufacture.

Figure 3. Commercial or finished excipient(s) are added to the in-process stream of an excipient's manufacture during co-processing. Figure courtesy of the authors.

Figure 4. During excipient manufacture, the in-process streams are combined before drying to produce a co-processed excipient. Figure courtesy of the authors.

What Are the Safety and Regulatory Considerations?

An important safety consideration for CPEs is that no new covalent bonds are formed during co-processing, and that starting material chemical identities are preserved. Therefore, the individual component safety profiles are largely carried forward into the CPE. Because co-processing integrates components at the particle level, some attributes and interactions (eg, surface chemistry, dissolution rate, or microenvironmental pH) may change and should be evaluated.

One regulatory challenge arises when CPE manufacturers cannot claim straightforward pharmacopeial compliance for the co-processed excipient, and not all co-processed excipients have established compendial standards. This gap leads to an open industry question: Would broader pharmacopeial monograph coverage increase acceptance and adoption of CPEs? Many in the field insist yes — standardized monographs could improve transparency, harmonize quality expectations, and streamline regulatory reviews — but developing those monographs requires robust, widely accepted characterization methods for composite materials.

To adopt co-processed excipients responsibly, formulators and manufacturers should apply the following core principles:

Demonstrated safety. Confirm that the component identities and toxicological profiles are acceptable and that no unintended chemical reactions have created new risks.

Consistent composition. Ensure strict control of raw material attributes and manufacturing parameters to maintain reproducible CPE composition.

Reduced variability. Leverage co-processing to achieve more consistent performance from batch to batch versus simple blends.

Process control and monitoring. Implement robust in-process controls and validated manufacturing processes to maintain quality.

Documented performance benefits. Provide evidence that the CPE delivers functionality that cannot be achieved by simple mixtures.

Benefits for Manufacturing, Sustainability, and Innovation

Co-processed excipients provide a range of benefits that address both operational and formulation challenges, such as the following:

Facilitation of continuous manufacturing. CPEs can reduce the number of feeders and simplify input streams, improving feed-rate consistency and enabling more efficient continuous processes.

Sustainability. By reducing development iterations, waste from formulation trials and rejection during production, co-processed excipients can lower environmental impact. Some CPEs support direct compression, avoiding wet granulation and the associated solvent and energy use.

Productivity and cost. Enhanced flow, compressibility, and robustness reduce downtime, rework, and rejection rates, improving throughput and lowering the cost of goods.

Formulation enablement and innovation. CPEs can overcome flow or compaction limitations, reduce strain-rate sensitivity, allow capsule-to-tablet conversions, reduce binder needs, and enhance stability — opening pathways to novel dosage forms or improved patient-centric products.

Co-processed excipients are a practical, increasingly common resource for modern pharmaceutical development and manufacture. By integrating complementary excipient functions at the particle level, CPEs deliver real performance advantages that simple blends cannot match — from enabling continuous manufacturing and improving sustainability to solving difficult formulation problems. Continued development of compendial standards and transparent characterization will further support safe, consistent adoption of these materials across the industry. For formulators and manufacturers seeking reproducible, high-performance inputs, co-processed excipients merit serious consideration to accelerate development and improve product quality.

General glossary of terms and acronyms for pharmaceutical excipients. Version 3. IPEC; 2023. Accessed April 8, 2026. 

IPEC-Americas. Co-processed excipients demystified. 

. 2024;1(2):60-63. Accessed April 8, 2026. 

https://jefc.scholasticahq.com/article/124082-co-processed-excipients-demystified

Gina Marsee is the director, Compendial Compliance and Advocacy at Merck located in West Point, PA, USA. She holds a bachelor’s degree in Chemistry & Biology from the University of Tennessee and has worked in the pharmaceutical industry for 30+ years holding various leadership roles within Quality, Compliance, and Regulatory Affairs. She is also Chair, IPEC-Americas.

Ms. Katherine Ulman is the owner and Primary for KLU Consulting, LLC. She retired from Dow Corning Corporation after more than 40 years of employment. While at Dow Corning, she held positions as a global regulatory compliance manager for their Healthcare business as well as regulatory manager of the Dow Corning Healthcare Industries Materials Site

Joseph Zeleznik is the Technical Director – North America at IMCD US LLC. Joseph brings nearly four decades of experience in pharmaceutical excipient and formulation development. His expertise spans high-functionality and novel excipients, continuous manufacturing, and advanced formulation strategies. Additionally, he is a member of IPEC-Americas Executive Committee, currently serving as Immediate Past Chair.

Candy Reynolds Cummings spent 15 years at GlaxoSmithKline starting as an analytical chemist and working up to QA Validation Manager in the OTC area (specifically oral care). Currently working at Evonik as the Regulatory and Product Stewardship Manager supporting the business line Silica for regulations in US, Canada, and Mexico.

Priscilla Zawislak is Corporate Regulatory Affairs, ROQUETTE AMERICAS, INC.
Priscilla has over 35 years’ experience in Regulatory Affairs and Quality for excipients, food additives and ingredients for personal care products. She is currently President of the IPEC Federation and the Vice Chair of Science and Regulatory Policy for IPEC-Americas and is also a past Chair of the organization.

Bob Sulouff is Sr. Manager Regulatory Affairs, Health & Pharma Solutions, ROQUETTE AMERICAS, INC. Bob has over 25 years’ experience in Regulatory Affairs and Quality, primarily focused on excipients. He is a member of Roquette’s Health and Pharma Solutions Regulatory team, where he advocates for value added pharma regulatory solutions. He is also Chair-Elect, IPEC-Americas.

David R. Schoneker is currently the president/owner of Black Diamond Regulatory Consulting, LLC, a consulting firm specializing in providing regulatory and quality consulting for the pharmaceutical, dietary supplement, food, and related industries. Dave has been involved in the excipient industry for over 48 years and is currently the Chair of the IPEC-Americas QbD/Composition Committee.

Articles

Co-processed excipients (CPEs) are engineered combinations of two or more excipients integrated at the particle level to deliver functional performance unattainable through simple blending, without significant chemical change. Longstanding examples exist, and more than 100 CPEs are now reported in commercial use, including compendial materials. Manufacture can involve processing finished excipients together or co-processing in-process streams, shaping morphology and key attributes affecting flow and compressibility. Safety expectations hinge on preserved chemical identities, while regulatory adoption is constrained by limited monograph coverage and characterization standardization.

This article details what co-processed excipients are and how they are made.

Co-Processed Excipients: Practical Engineered Solutions for Modern Pharmaceutical Challenges

Beige cosmetic or make up powder isolated on white. | Image Credit:©triocean – stock.adobe.com

An essential factor to consider when developing a robust continuous manufacturing (CM) process is the impact that inherent excipient and API physicochemical variations can have on the drug product performance, CM unit operations, or CM process as a whole.

This paper examines the key information needed for excipients and their potential impact on CM processes. Much of this information is derived from several presentations made at a 

 (PQRI) workshop entitled, “Managing Excipient and API Impact on Continuous Manufacturing”, held virtually on May 17–18, 2022 (1).

CM involves continuous feeding of input materials into, the transformation of in-process materials within, and the concomitant removal of output materials from an interconnected manufacturing process in which two or more-unit operations are directly integrated. While many excipients have been continuously manufactured for decades, the use for pharmaceutical drug products, particularly oral solid dosage (OSD) forms, is relatively new. Knowing how excipient physicochemical properties impact CM, whether as a whole or in individual unit operations, needs to be understood to implement a rigorous control strategy and ensure a robust CM process. Not every excipient will have a direct impact on the overall process but may affect individual unit operations to some degree.

Most regulatory guidelines apply only to APIs and drug product manufacture but not excipients (e.g., International Council for Harmonisation [ICH] Q13 [2]). However, regulators and other organizations are discussing what impact excipients may have on CM and what controls or understanding are needed to ensure success in the development and manufacture of pharmaceutical products through continuous processes. One example is International Pharmaceutical Excipients Council of the Americas (IPEC-Americas) and how the various IPEC guides may assist in understanding the role of excipients in CM.

CM is also gaining traction in the manufacture of biologic drug substances and their dosage forms. Many biologics are liquids intended for injection and excipient considerations for CM of liquid biologic drugs are quite different than for OSDs. This article will focus on CM for OSDs.

CM offers efficiency, cost-effectiveness, and real-time quality control in a reduced footprint compared to traditional batch manufacturing. However, this shift from batch-based to continuous production hinges on one critical factor: understanding and controlling the material properties of the raw materials involved.

A growing body of knowledge is being developed on this topic for CM of liquids, semisolids, and OSDs. The majority of FDA- and European Medicines Agency (EMA)-approved commercial CM drug products are OSDs, particularly tablets, manufactured via direct compression or twin-screw granulation platforms.

The following sections focus on highlighting the importance of characterizing raw materials and understanding their variability for manufacture of OSDs. General considerations based on unit operations and specific case studies are provided.

Why are material properties so important? 

The impact of raw material properties on process performance and drug product quality has been extensively studied. Understanding this impact does not automatically translate to robust processes and products. Control strategies to accommodate the impact of raw material variability should minimize the number of alarms and process interruptions and give robustness and consistent product quality.

For continuous manufacturing of OSDs, the following are three major reasons why it is important to proactively evaluate the impact of raw material properties:

 Variations in material properties can impact product critical quality attributes (CQAs) such as drug release, potency, and ultimately, patient safety.

 Predictable material properties reduce the risk of mass flow deviations from their set point, minimizing alarms and process downtime, and maximizing process and process analytical technologies (PAT) model robustness. Robust models require less updates and, if used for real-time release, reduce downtime and supply chain disruptions.

 Tailoring process parameters based on material properties (e.g., via design spaces) can improve efficiency, yield, and overall cost-effectiveness (faster return on investment [ROI]) of the manufacturing platform.

Powder properties that impact unit operations in CM. 

CM, when optimized, allows for enhanced predictability and control. Understanding the impact of raw material variability on process performance will allow for the design of a control strategy that ensures continual high drug product quality. A comprehensive list of all the material properties that can impact formulation and process development of liquids, creams, gels, and OSDs, is outside of the scope of this article. To date, most CM approvals have been for OSDs. The following is a list of the material properties to consider for manufacturing pharmaceutical tablets or capsules:

Particle size distribution can impact flowability, cohesion, mixing dynamics, blending time, and granulation torque.

Bulk density needs to be considered in feeder design. Light, fluffy powders are more difficult to feed and compress, and may require pre-blending steps before incorporation in a continuous process line.

Surface area and morphology properties can influence electrostatics or tribocharging, tablet ejection force, drug dissolution, and film coating effectiveness.

Flowability and cohesiveness (inverse correlation) determine powder handling, feeding configurations, mass flow alarms and noise/smoothing averages, blending efficiency, pre-compression parameters, and others. A shift in excipient or API cohesion can impact its flowability and thus how efficiently it fills screw flights. These differences can require new feed factor calibrations (grams delivered per revolution) and control parameter tuning on screw speed to reach the mass flow setpoints. Additionally, poor flowing blends can introduce increased tablet and capsule weight variability and thus impact overall assay. Paradoxically, a free-flowing blend can also segregate more easily as it moves downstream to the tablet press or capsule machine and flood the dies wherein increased tablet weight variability is the system response.

Compressibility refers to changes in powder volume as an effect of applied normal force. Excipients with higher compressibility are generally more cohesive (they can function as binders) and are sensitive to shear. Increased head pressure when charging material into the feeder hopper (refill) will increase powder packing and, for highly compressible materials, this can lead to bridges and densification in the screws, ultimately negatively impacting mass flow variability. Refill limits and charging systems (manual vs. pneumatic, for example) should be designed with material compressibility in mind.

Moisture content impacts blend hold time (potential for microbiological contamination), powder flowability, tribocharging, tableting properties, and drug product stability.

Characterization technique considerations. 

Performance-related properties—the physical characteristics of excipients that may impact performance and drug product manufacturability—are generally not comparable due to multiple, non-standardized methods. Formulators are then required to test these as part of product development and include the results in risk assessments and regulatory submissions that contain the product knowledge and history.

For example, particle size distribution can be determined by laser diffraction or sieve analysis, and other techniques. Flowability can be described based on Hausner Ratio, Carr’s Index, Angle of Repose, or powder rheometry. Considering that there are multiple ways to test an attribute, the details of the method are as important as the results to allow comparability.

Having standardized methods offer several benefits:

Data comparability enables consistent comparison of data across different labs, sites, and batches.

if methods are standardized, sites can share a raw material database with known interactions with their unit operations (process performance) and drug product quality. This would allow for a prediction of process and product robustness, such that precise adjustments to process parameters like refill limits and blending speeds can be tuned based on factors like compressibility and flowability. This ensures consistent product quality throughout continuous production.

Improved communication and collaboration—standardized data creates a common language for communication among scientists, engineers, and regulators. This can allow for faster technology and product transfer amongst company sites, and clear communication from the user to the excipient supplier and vice versa in cases of investigations.

Reduced costs and risks—accurate and comparable data minimizes the need for extensive re-testing and troubleshooting, leading to cost and full-time equivalent (FTE) savings, and reduced risk of production delays associated with inconsistency in raw material behavior.

The successful implementation of CM in the pharmaceutical industry relies heavily on the reliable assessment of raw materials—both excipients and API. Inconsistency in raw material properties can have a domino effect, impacting process stability, product quality, and ultimately, patient safety. Standardizing characterization techniques can mitigate these risks and ensure successful CM implementation.

Impact of material properties and variability on continuous manufacturing

To understand excipient variability, it might be helpful to understand several factors. Excipients, particularly those that are naturally derived or quarried and refined, often have complex multicomponent compositions. Changes in seasonal growing conditions, for example, may result in varying composition, even if only slight, which could impact physical and/or functional properties. Unlike many pharmaceutical products, excipients are sometimes manufactured on a metric ton scale, often by CM. This leads not only to batch-to-batch variability (inter-batch variability), which is often monitored, but also excipient intra-batch variability, or package-to-package variability. While a well-designed, robust continuous process for drug product can manage excipient variation that might otherwise adversely affect process, product quality, or performance, understanding slight variations within an excipient (or API) batch can assist in designing a robust CM process.

Raw material properties, both physical and functional, can impact process behavior due to the particle–particle interactions taking place throughout the equipment train. Using a quality-by-design (QbD) approach to understand material attributes and their impact on the process and product can facilitate better product robustness. Individual ingredients should be characterized for their intended role in a formulation in addition to how the interactions among ingredients impact the CM process and product quality. For example, understanding segregation tendency during manufacture may help with ingredient selection before moving forward with process design. By understanding the critical material attributes, and modeling one or more continuous process designs, the best outcome can be achieved.

Excipient variability can also lead to changes in the PAT signal and consequent analysis. PAT feedback is critical in implementing an adequate control strategy and ensuring a robust CM process.Without a defined control strategy with PAT input, process drift could lead to product or process failure, affecting yield. Assessing the effect of material changes on residence time distributions and from there on, establishing actionable system responses to disturbances are key to ensuring consistent product quality and process performance. Given the limitations of material introduction into the continuous process, excipient performance then assumes greater importance in CM.

CM provides the ability to isolate non-conforming material without compromising the batch in its entirety. CM also mitigates much of the tech transfer risk associated with traditional batch manufacturing, primarily through elimination of scale-up. However, CM by itself does not mitigate raw material risk. Formulation design should be guided by the finished product CQAs regardless of whether the product is manufactured continuously or batch-wise. CM reduces the process degrees of freedom relative to batch manufacturing, but not the impact of raw material variations.

The output from a continuous manufacturing run is variable, dependent on run time, in contrast to the fixed output from a batch process, which is dependent on equipment size. The ICH Q13 guideline includes an example of a CM tablet noting that “the continuous process verification approach, coupled with appropriate regulatory action for reporting manufacturing changes, was used to validate run time extensions beyond current experience” (2). Excipient selection should consider potential risks from extended running, such as fouling of tooling.

Excipients should not need tighter specifications in CM than in batch processing. The process should be designed such that any transient disturbances associated with raw material variability are averaged out according to the residence time distribution of the CM process. Excipient variability may be more visible due to PAT, as the smaller working volumes in CM allow better temporal and spatial correlation with excipient variability.

In CM, the significance of a disturbance is a function of its magnitude and duration. The robustness of CM is demonstrated by the example in the ICH Q13 guideline where a disturbance of ±20% lasting less than 90 seconds would not cause the drug concentration in the blend to exceed the 90–110% label claim (see 

). Similarly, for a ±5% disturbance of 300 seconds or 5 minutes, the product would still meet label claim. 

It is likely that CM will provide more insight into excipient impact especially if the greater amount of PAT data associated with CM can be subjected to multivariate analysis. The IPEC QbD guideline (3) provides methods for the categorization and control of excipients.

Figure 1. Example of a funnel plot for the feeding of a drug substance. (Figure courtesy of International Council for Harmonisation [ICH]. ©ICH, used under public license.)

Excipient traceability in drug product batches manufactured by CM

In CM, traceability is defined as “the ability to track the distribution of materials throughout the manufacturing process” (2). Traceability is required so that non-conforming material can be diverted. Understanding of the residence time distribution is required for traceability to control material diversion.

Traceability is also required to determine where individual batches of an excipient occur in the output finished product stream. If a second batch of an excipient is introduced into a CM run, there will be finished product initially containing excipient batch 1 only, then product containing increasing proportions of batch 2, and finally product with batch 2 only. Products may be conforming but the location of the transition material needs to be known in the event of a subsequent investigation or recall associated with an excipient batch. For this reason, it is advisable to time slice long runs into sequential smaller batches.

The need for excipients designed for purpose

The need for new excipients has never been greater nor the benefits clearer. Novel excipients with improved properties can enable API solubilization, consistent product mass flow, more precise PAT measurements, and in some cases, better pharmacokinetic profiles with improved dosing regimens and higher product efficacy. In CM, co-processed excipients (CPEs) have emerged as a fit-for-use alternative to simplify formulations. CPEs are multi-functional and have many of the desired functionalities required to develop CM drug products. The formulation approach is simple: combine the API with the CPEs via blending, and compress. The CM process approach with CPEs is also rather simple, as the manufacturer would only require a minimum of two feeders, when appropriate, greatly reducing the complexity of the control strategy compared to traditional five- to six-component drug products.

Excipients have always played a critical role in drug product processing, and there is a need for material innovation to enable further adoption of CM from traditional batch manufacturing.

The information provided above has demonstrated how important excipient properties are to the success of CM. However, there are some challenges and opportunities with the use of current excipients in CM processes such as the following:

Ultra-low-density materials, such as fumed silica, cannot be fed unless preblended.

High regulatory uncertainties related to CPEs.

Excipients need stronger PAT signals to distinguish more easily from API spectra.

Excipients could help mitigate fouling of CM lines and enable more efficient clean in place (CIP).

There are few incentives for excipient innovation (e.g., FDA Pilot Program for the Review of Innovation and Modernization of Excipients [PRIME] [4]).

Regulatory and industry perspective on how to mitigate risks

Excipient attributes often vary between suppliers, even for the same grade. They may have differences in properties such as particle size and flowability which can affect process variability in CM runs. As such, sourcing excipients for CM will likely lead to detailed negotiations in supplier quality agreements wherein compliance with the pharmacopeia monograph tests will not be sufficient and customer-specific tests and specifications will become more important.

Considering that formulations with more excipients can potentially have more variability when raw materials are sourced from different suppliers, co-processed excipients (CPEs, combinations of two of more excipients into one) can benefit both batch and CM processes. Particularly for CM, formulating with CPEs has the advantage of reducing the number of process feeders and simplifying the control strategy. Although advantageous for accelerating formulation design and maximizing process robustness, the use of CPEs present a supply chain risk as they are sourced from a single supplier. This risk needs to be discussed during supply agreement negotiations, in addition to the compliance / testing topics described earlier.

For both batch and CM products, there is an expectation on the part of regulatory agency review staff that risks to finished product quality (CQAs) will be assessed and understood, critical material attributes (CMAs) identified, and risk mitigation strategies, including extra testing as needed, will need to be put in place. There is also an expectation that such information will be included in regulatory filings. The implementation of risk mitigation strategies to reduce the impact of the risks identified in the risk assessment, including supply chain, will likely influence the final choice of excipients.

As CM becomes more common, excipients that traditionally have been used may not provide optimal CM formulations. There will be a greater need for innovation and the use of new excipient technologies to provide enhanced properties designed for purpose in CM applications. It will be more important than ever to develop improved regulatory strategies to provide the incentives needed for this innovation.

It is hoped that the development of FDA’s PRIME program which allows for an independent safety assessment of different novel excipient types will open the door to the innovation needed to support successful implementation of CM going forward.

1. PQRI. “Managing Excipient and API Impact on Continuous Manufacturing”. PQRI Workshop May 17–18, 2022.

Continuous Manufacturing of Drug Substances and Drug Products

Incorporation of Pharmaceutical Excipients into Product Development Using QbD Guide

4. FDA. Pilot Program for the Review of Innovation and Modernization of Excipients (PRIME). FDA.gov.

Krizia M. Karry, PhD, ishead of Global Technical Marketing, Pharma Solutions, BASF. Brian Carlin is president and owner of Carlin Pharma Consulting LLC. Nigel Langley, PhD, MBA, is global technical director at Gaylord Life Sciences and Immediate Past Chair, IPEC- Americas. R. Christian Moreton, PhD, is partner, FinnBrit Consulting. David R. Schoneker is president and owner of Black Diamond Regulatory Consulting. Katherine L. Ulman is owner and president of KLU Consulting LLC. Joseph Zeleznik is technical director North America at IMCD.

Key information is needed for excipients and their potential impact on continuous manufacturing processes.

Understanding Excipient Characteristics to Ensure Robust Continuous Manufacturing 

Excipients are substances other than the API, which have been appropriately evaluated for safety and are intentionally included in drug delivery systems. Excipients are typically more complex than APIs, because they are frequently multi-component and less well-defined. In addition, excipient variability can present itself in various forms, compositionally, physically, or functionally.

Most excipients are not pure substances. Other residual and trace components present in excipients can impact key excipient functional characteristics when used in pharmaceutical formulations (1). The International Pharmaceutical Excipients Council (IPEC) refers to these other unavoidable substances in excipients as concomitant components (2). Performance of many excipients in a drug formulation may rely on the presence of such substances in the excipient. These excipient components are not considered impurities and could vary due to changes in raw materials, process variability, and from supplier to supplier. Excipients are not controlled at an individual parameter level. There are many degrees of freedom associated with polydispersity of particle size, molecular weight, and chemical composition, all of which may be process or supplier dependent. Particle size is usually controlled as an average or distribution, and dilute solution viscosities are often used for routine analysis to monitor batch-to-batch consistency of polymer molecular weight. The composition profile of a complex mixture may not be well defined, and the performance impact of the many components may not be well understood.

Silverstein contrasted the control of API quality versus that of excipients (3):

“API quality is improved by reducing the presence of all materials other than the desired chemical. […] Extraneous substances may be harmful to the patient in that they may lead to side effects, or they are inert, thus reducing API purity and thereby compromising efficacy.”

“Excipient quality is described quite differently. While one would again refer to compliance with the compendial monograph (if there is one) or the manufacturer’s specification, a higher assay is not always better. While this may seem counterintuitive, excipients are often complex mixtures that include constituents arising from raw materials, catalyst, solvent, initiator residue, or side reactions” (3).

Excipients are often mixtures of materials with major and minor components, and the minor components may contribute to the overall excipient performance in a particular application (4). For example, the compactibility of coarse grade dibasic calcium phosphate dihydrate is influenced by the presence of “impurities” in the crystal lattice, which cause dislocations and weakness, allowing brittle fracture to occur. Very pure coarse-grade dibasic calcium phosphate dihydrate does not compact as well. However, in general, the exact
relationship between excipient composition and excipient performance is not often well understood and will vary with each application (5).

Many excipients possess some inherent variability. Variability in the finished excipient attributes can arise from many sources such as, but not limited to those in 

Table I. Potential variability due to excipient source.

Excipient variability for some excipients can also be influenced by degradation, which also can be impacted by packaging and/or environmental conditions during storage and distribution.

As described in the IPEC quality-by-design (QbD) guide (6), “excipient manufacturers can control excipient variability only within the limits of their process capability and for which the processing equipment was designed and constructed.” Process capability is a general statistical concept based on the ratio of the specification limits to the process variability. If the variability is the same as the specification range the process capability is one, with no room for error. The higher the process capability the lower the risk of failure. Less than one means that not all batches will meet specification. Therefore, arbitrary narrowing of a specification by users may adversely impact sustainable excipient supply. Robust formulations are not critically impacted by typical excipient variabilities, not all of which may be reflected in the specification.

“In addition, the equipment train used in the process and the type of processing and unit operations included may all influence variability. Various excipients are continuously manufactured in many metric tons per annum. Results reported on a certificate of analysis (CoA) will often be a composite or average, potentially underestimating variability. Not all excipients will have the crystallization or precipitation steps typically used to purify fine chemicals. Users should discuss inherent variability with the supplier and their capability to supply product as it relates to the user’s needs (7). It is the responsibility of the user to identify potential critical material attributes (CMAs) for the excipients used in their formulations but the suppliers may be able to assist. A risk-based approach will probably be appropriate” (6).

Different excipient manufacturers are likely to use different raw material sources as well as different manufacturing processes. Therefore, variability introduced by alternate sources encompasses variability of both raw materials and processing.

Excipients from alternate sources (additional sites within a manufacturer and/or alternate supplier(s)) may not be compositionally, physically, or functionally identical, but may still demonstrate equivalent performance within the drug product depending on application. Excipient users should define functional performance requirements for alternate excipient sources (8).

When evaluating alternate excipient sources, users should not assume that all sources conforming with the same compendial requirements are interchangeable in all drug product formulations. Variability in excipient composition and other attributes among excipient sources could impact performance. To gain an understanding of the potential origin for various components that may be found in excipients from different sources, see 

Figure 1. The complexity in excipient composition. Figure courtesy of IPEC Americas.

Confirmation of equivalent performance is necessary to support interchangeability. The critical quality attributes (CQAs), including stability, of the drug product manufactured with the alternate source must be demonstrated.

Distributors should not substitute an alternate excipient source without prior notification to the excipient user to allow evaluation of the interchangeability of the alternate source in their specific drug applications.

In a 2008 article on “Comparative Tableting Properties of Sixteen Microcrystalline Celluloses” (9), Doelker 

noted that, “Great differences in packing and tableting properties and in sensitivity to the addition of a lubricant were generally observed between
products from the various manufacturers. In contrast, lot-to-lot variability was quite acceptable.”

Mitigating the impact of excipient variability

Moreton defined a robust formulation as being “able to accommodate the typical variability seen in API, excipients, and processes without compromising the manufacture, stability, performance, or any other attribute of the product critical to the patient’s care or well-being” (5).

Qualifying multiple sources should be considered when establishing the design space to reduce the time required to switch to an alternative supply after launch (10). If the impact of an excipient variability on finished product CQAs is unacceptable, then additional controls (CMAs) should be considered. Both limits and methods for CMAs must be agreed between user and excipient manufacturer.

It may be necessary for excipient manufacturers to make changes to their processes for various reasons that have the potential to impact excipient performance and thus finished product performance. Excipient manufacturers should consult the IPEC Significant Change Guide for Pharmaceutical Excipients (11) whenever a change is to be made to excipient raw materials, manufacturing process, and/or finished excipient testing and assess the need for customer notification. Based on a risk assessment, the excipient manufacturer should apply the same reasoning (as far as is practicable) to their own suppliers of starting materials, reagent, solvents, processing aids, and additives used in the manufacture of the excipient.

When investigating potential impacts of notified changes, it is strongly recommended that a risk assessment be undertaken by the excipient user. Based on the results of the risk assessment, the excipient user should determine their need for further action.

It may be necessary for the excipient user to build product inventory, thus requiring pre-change excipient supply, because regulatory filings may be subject to extended review times. This may, in turn, require coordination between excipient manufacturer and user.

It should also be remembered that not all changes to an excipient will be detrimental to the performance of the excipient or pharmaceutical finished product. All changes should be considered as significant unless it can be scientifically justified as not a significant change. Significant changes should be notified to the excipient user (11).

Factoring excipient variability into design of experiments, control strategy, and lifecycle management will increase finished product robustness (12),
which will improve the overall product quality and performance, leading to better patient outcomes.

Excipient variability should always be a concern unless proven otherwise. Relying only on the excipient sales specification or the compendial monograph is not enough to account for potential variation(s) because many CMAs may not be part of these requirements. Drug product manufacturers should have a robust dialogue with their excipient suppliers to understand the variability of material attributes.

PharmTech APIs, Excipients, and Manufacturing 

Composition Guide for Pharmaceutical Excipients

I. Silverstein, “Excipient Quality and Selection,” PharmTech Europe, 28 (2) 2016.

Incorporation of Pharmaceutical Excipient into Product Development using Quality-by-Design (QbD) Guide,

The IPEC-Americas Quality by Design (QbD) Sampling Guide, 

E. Doelker, D. Mordier, H. Iten & P. Humbert-Droz (1987) Comparative Tableting Properties of Sixteen Microcrystalline Celluloses, 

, 13:9-11, 1847-1875, DOI: 10.3109/03639048709068696

Qualification of Excipients for Use in Pharmaceuticals

Signifiant Change Guide for Pharmaceutical Excipients

CPhI Pharma 2021 Report: Post Pandemic Legacy Trends

Brian Carlin is owner Carlin Pharma Consulting LLC. George Collins is the Vice-President for Excipient Mineral Manufacturing, RT Vanderbilt Company. Chris Moreton is partner at FinnBrit Consulting. David R. Schoneker is the President/Owner of Black Diamond Regulatory Consulting, LLC. Jennifer Putnam is a Senior Supervisor, Analytical R&D at Perrigo.Joseph Zeleznik is Technical Director, North America for IMCD US Pharma. Katherine Ulman is the owner and Primary for KLU Consulting, LLC. Stacey Bremer, Director, Product Stewardship Medical at Celanese.


Vol. 46, No. 8
August 2022
Pages: 20–23

When referring to this article, please cite it as B. Carlin et al., “Mitigating the Risk from Excipient Variability,” 

This article reviews sources of excipient variability, including raw materials and processing, both of which may vary from supplier to supplier and from plant to plant for a single manufacturer.