Richard J. Forsyth is principal consultant with Forsyth Pharmaceutical Consulting, 907 Shamrock Ct, Royersford, PA 19468, tel. 484.535.1688, forsythpharmaconsulting@gmail.com.

Richard J. Forsyth

A cleaning procedure is expected to remove soil from product-contact equipment surfaces. A validated cleaning procedure has been shown to reliably remove soils from these surfaces. One of the accepted approaches to cleaning validation is to identify a worst-case soil for validation. A worst-case soil is one that is the most difficult to clean in relation to all other soils manufactured in a pharmaceutical facility. If the worst-case soil can be cleaned to an acceptable level, it can be concluded that the other soils in the facility can also be cleaned to an acceptable level using the validated cleaning procedure.

Identification of a worst-case soil can be accomplished through equipment-washer and formulator experience. Those involved in manufacturing formulations, cleaning, and maintaining the equipment are in the best position to identify the hardest-to-clean soil. This approach is a practical but subjective determination and would leave a facility open to question until ongoing data supports the initial conclusions on the worst-case soil.

A second approach is a comparison of API solubility. Solubility data for APIs are typically generated in water and organic solvents as part of the physical and chemical characterization workup for the API. Those APIs that are least soluble in the cleaning solvent are considered the hardest to clean. This approach neglects the formulation excipients, which are often insoluble, comprise a much greater percentage of the formulation, and can be more difficult to clean than the API. 

A more empirical method to determine a worst-case soil is to spot coupons with the soils, allow them to dry, and clean them using the identical conditions encountered in the cleaning cycle. Equipment surfaces, however, encounter different types of cleaning action depending on their location in the manufacturing equipment. Soils could be subjected to manual scrubbing, impingement under the cleaning solvent, turbulent flow from a pump forcing cleaning solvent through piping, or a cascade action as the cleaning solvent moves across equipment surfaces. 

Cleanability studies are typically conducted using dried residue spotted on a coupon dipped into a beaker containing water or the cleaning solvent or solution. The cleaning solvent is stirred, creating a less rigorous cleaning action than encountered during actual cleaning, and would be considered a worse-case condition. The experiment can be conducted at room temperature or an elevated temperature. The soil with the longest cleanability time can be considered the worst-case soil for cleaning validation within the variability of the test parameters. Numerous studies have been conducted to demonstrate cleanability. Studies range from a paper-based evaluation of a facility’s soils (1) to basic laboratory conditions, such as suspending the coupons in a beaker of cleaning solvent, all the way up to a sophisticated cleanability bath (2). Cleaning parameter variations have been characterized using cleaning process design on bench-scale studies (3), but for this study the cleaning parameters were held constant. Statistical equivalence testing for assessing cleanability (4) can show that soils are cleaned to an equivalent extent. If potential worst-case soils demonstrate comparable cleanability, it would be prudent to use more than one worst-case soil for further testing. 

A well-executed cleanability study is one part of a comprehensive cleaning validation program. The experimental cleanability can be preceded by an evaluation of the formulation components to narrow the number of soils tested. The selected soils and materials of construction can be tested using a matrix approach to determine a worst-case soil and a hardest-to-clean material of construction.

Complementary studies can include—rinse recoveries and swab recoveries for analytical testing, and visible residue limits (5) for inspection of cleaned equipment. The studies can be conducted in parallel, often using the same coupon samples for multiple studies. All studies might not be necessary, based on the number of formulation soils and the manufacturing equipment involved, but a comprehensive picture of the physical properties of the soils during cleaning, and the ability to test and detect residual soils after cleaning, form a sound basis for a validated cleaning program.


The cleanability study was conducted to determine ease of cleaning for a variety of soils on a range of material-of-construction coupons using the following parameters. 

 lists 10 material-of-construction coupon types, which are among the commonly used materials of construction in pharmaceutical and biopharmaceutical manufacturing. All 10 materials of construction were tested during the study.

The cleanability study to determine the worst-case soils was conducted using three buffers and three media under the following parameters. The coupons were weighed and soils were spotted in triplicate for each of the material-of-construction coupon types listed in 

 Each individual coupon was spotted with 1 ml of the soil. The soil was allowed to dry for at least 4 hours, or until visually dry, but no longer than 3 days, which was the established dirty hold time. Following drying, the coupons were reweighed and the coupon weight was subtracted to determine the weight of the residue. The coupons were immersed in a 600-ml beaker containing 400 ml of room-temperature purified water. The 600-ml beaker was the smallest beaker that would hold the 2.5” x 2.5” coupons without impeding flow around the coupons during testing and 400 ml was the minimal volume necessary to completely cover the coupons. The water was agitated on a magnetic stirrer at a fixed rotation and did not generate a vortex during testing. The cleanability endpoint was defined as the time at which the soil was no longer visible to the observer under defined conditions: distance 18 inches, optimal viewing angle dependent on the material-of-construction coupon type, and 700 lux light intensity. The coupons were removed from the beaker immediately after the visual endpoint was determined. 

The visual endpoint was confirmed analytically through conductivity, total organic carbon (TOC), and gravimetric testing. The cleaning solution in the beaker was tested for conductivity. A sample of the cleaning solution was taken and tested for TOC. Positive controls were tested for conductivity and TOC by pipetting 1 ml of soil directly into a beaker and testing for conductivity and TOC. After drying, the coupons were again weighed and the weight was compared to the initial weight to determine cleanability of the soils gravimetrically. 


The material-of-construction coupons chosen for the study were seen as representative of a wide variety of materials. A number of liquid soils were chosen to represent a sampling of pharmaceutical and biopharmaceutical soils. Implementation of this approach at a site should address all soils on all materials of construction employed at the site unless an abbreviated approach can be justified.

Instruments were checked with every use to ensure they were operating properly and within calibration dating. The soils and the cleanability results along with supporting TOC and conductivity data are presented in the following sections.

Two buffers (regeneration buffer and zinc wash buffer) were spotted and held for 3 days to match the proposed dirty hold time maximum, but these buffers did not dry due to high ethylene glycol content. It should be noted that a properly executed paper-based evaluation (1) would have eliminated these two soils from the laboratory testing and saved 2 days of waiting for each of the trials. The assays for these two buffers on 316-finish stainless steel were representative for all of the materials of construction. 

The visual removal data generated for the soils as shown in

 demonstrated complete removal of the soils from all materials of construction. The data in 

 are expressed as an average of the three individual determinations. Times vary widely, with the two buffers that did not dry rinsing from all coupons within 10 seconds. The 316-finish stainless steel and nickel-steel alloy (Hastelloy) coupons were the only materials of construction that demonstrated retention of the other four soils. They provided a representative ranking of the cleanability for all the soils and comprised the vast majority of material-of-construction surface area for all automated cleaning circuits. Ethylene propylene diene monomer (EPDM), silicone, polytetrafluoroethylene (Teflon), and synthetic fluoropolymer rubber (Viton) all became visually clean quickly for all soils, making any type of soil ranking difficult on those materials. Of the remaining four material-of-contruction coupon types: acrylic, glass, polypropylene, and polyether ether ketone (PEEK), all retained some soils but not others. These inconsistent results were coupled with the fact the soils retained by these materials were also retained strongly by 316-finish stainless steel and nickel-steel alloy (Hastelloy). Visual endpoint testing is subjective, and therefore, should be done in multiples by a small, well-trained personnel group to maintain consistency for the observations. 

 demonstrated high percentage of removal from all of the materials of contruction for each of the soils except for the regeneration buffer with 20% ethanol, which evaporated during the coupon drying. Removals greater than 100% can be attributed to day-to-day variance in calibration of the conductivity meter. Conductivity, however, could be misleading. The conductivity readings began to plateau well before the coupons became visually clean. The conductivity levels of the fully dissolved soils were relatively low (<60 µS/cm). Use of conductivity measurements should confirm the conductivity of the soils and should graph the rate of soil removal during cleanability testing and compared to visual endpoint measurements. 

 show complete removal of the residues. Other than 316-finish stainless steel, glass, and nickel-steel alloy (Hastelloy), the material-of-construction coupon types demonstrated some results where the final weight was less than the initial weight, indicating that the coupons continued drying over a number of days at ambient temperature. This observation makes all other materials of construction poor candidates for the initial cleanability unless they are oven dried and could affect the speed and accuracy of a study. Continued use of gravimetric measurements for the 316-finish stainless steel and glass coupons would provide data of limited value, given that gravimetric testing demonstrated complete soil removal but did not provide an endpoint determination. Other testing is necessary in conjunction with gravimetric determinations. 

TOC testing results, as shown in Table V, were reasonably consistent with the conductivity and gravimetric. One soil, phosphate buffered saline, had no organic carbon to measure and was, therefore, not applicable for this test. The results for the first media were consistently high, as were the conductivity results. The most likely cause would be a low positive control, but because the gravimetric results were consistently good, a repeat of the experiment was not necessary. Most soils required multiple dilutions prior to TOC testing, and testing was time-consuming compared to conductivity and gravimetric testing making TOC a less attractive soil removal confirmation test. 

The evaluation of the data to identify the worst-case soil on the hardest-to-clean material of construction should be done in tandem. Table VI ranks the four retained soils on each material of construction from 1 to 4, with 1 being the hardest to clean. The rankings were then averaged across the soils and Media A was determined to be the hardest to clean soil by a small margin over the media with phenol red.

 ranks retention on the six out of 10 materials of construction that demonstrated retention characteristics. The four soils were ranked from 1 to 6, with 1 being the hardest-to-clean material of construction. The rankings were then averaged across the materials of construction and 316-finish stainless steel and nickel-steel alloy (Hastelloy) were determined to be the hardest-to-clean materials of construction by a wide margin.

The worst-case combination of soil and material of construction was Media A on 316-finish stainless steel or nickel-steel alloy (Hastelloy) for the soils and materials of construction tested. The soil and material-of-construction matrix at a facility can be combined into groups based on data and identification of a worst case. A similar analysis for swab recoveries (6, 7) identified stainless steel as a representative material of construction for most equipment and for a large majority of soils. The present study indicates a similar conclusion, (i.e., 316-finish stainless steel is a representative material of construction for cleanability), but the data set is too small to be conclusive. This type of grouping strategy should be explored for each facility to streamline experimentation while still presenting a comprehensive picture of the soils and materials of construction in manufacturing operations. 

Cleanability testing of the matrix of soils and materials of construction at a given site can cover all soils on all materials of construction or can be focused based on an evaluation of the components of the soils (1), coupled with preliminary testing over the range of materials of construction. The testing plan should be done within the overall cleaning evaluation including cleaning cycle development, swab and rinse recoveries, and visible residue limit determinations. 


Cleanability studies can provide objective data on the hardest-to-clean soil at a facility. Conclusions could differ based on the soils and materials of construction at a given facility. A similar survey of soils and materials of construction should, therefore, be executed. Measuring the cleanability endpoint should be done consistently, including visual observation and at least one other confirmation test. The resulting cleanability data can vary for different materials of construction depending on the soil, and an evaluation of the matrix of soils and materials of construction will provide a path forward for cleaning validation execution. 

For this study, based on the materials of construction and soils tested, it can be concluded that performing cleaning validation of the worst-case soils focusing on the 316-finish stainless steel or nickel-steel alloy (Hastelloy) surfaces with conductivity results to confirm visual results is an approach that will provide the most conclusive results. These materials have the added advantage of being the most frequently used materials of construction for all automated cleaning circuits. 

Although important, cleanability is only one aspect of a comprehensive cleaning validation program. Personnel cleaning experience, rinse recoveries, swab recoveries, visual residue limits, cleaning cycle development, and cleaning validation are all crucial elements of a well-defined, documented, and defendable cleaning program.

R. J. Forsyth, J. C. O’Neill, J. L. Hartman, 

Richard J. Forsyth is a senior consultant with Forsyth Pharmaceutical Consulting, 907 Shamrock Ct, Royersford, PA 19468, forsythpharmaconsulting@gmail.com; Keith Bader is senior director of technology and Kelly Jordan is an engineer, both with Hyde Engineering & Consulting, 6260 Lookout Road, Suite 120, Boulder, Colorado 80301. 


Articles

The authors look at the cleanability of pharmaceutical soils from a variety of materials of construction to determine the relative ease of cleaning and explore potential grouping strategies as part of a comprehensive cleaning validation program.

Cleanability of Pharmaceutical Soils from Different Materials of Construction

Visual inspection of pharmaceutical manufacturing equipment for cleanliness is required after cleaning procedures are completed and is a prerequisite for the start of manufacturing activities (1). Cleaning validation demonstrates that the cleaning procedure reliably and consistently cleans pharmaceutical manufacturing equipment to an acceptable level. Visual inspection is an active observation of the visually accessible product contact surfaces of the pharmaceutical manufacturing equipment. The visual inspection must determine that the equipment is free from any visible residues for the cleaning to be considered adequate and to allow manufacturing activities to commence. Although there may be other measures of adequate equipment cleaning, such as swab sampling, visual inspection is the first measure of equipment cleanliness.

Visual inspections are conducted by a variety of site personnel. Equipment-cleaning personnel routinely inspect equipment during a manual cleaning procedure and after completion. They inspect parts that have been cleaned in a parts washer. They inspect large equipment after manual cleaning or clean-in-place (CIP) procedures. Finally, they inspect closed-system equipment that is cleaned using a cleaning skid that pumps cleaning agents through piping to the equipment. Equipment cleanliness is documented in the cleaning record for the equipment

In addition to the equipment-cleaning personnel, visual cleanliness of cleaned equipment is routinely confirmed and documented in the cleaning record by a second person. Prior to manufacturing of the subsequent batch, equipment is routinely inspected for visual cleanliness by manufacturing personnel and documented in the manufacturing batch record. Quality and validation personnel also inspect cleaned equipment periodically as part of their work function.    

Training of personnel for visual inspection of cleaned equipment historically has consisted of on-the-job training conducted by experienced personnel. Documentation of the training was typically not in a unique, separate training record, but as part of general training for cleaning, operations, or quality. 

As part of a cleaning-validation program, personnel who take swab samples have been routinely qualified to determine that they can adequately recover residues from equipment surfaces.  Laboratory personnel are qualified for testing of the cleaning samples. Cleaning and testing procedures are validated to demonstrate consistent execution. A qualification criterion for visual inspection of cleaned equipment by personnel is a logical extension of this philosophy as part of a cleaning validation execution, and qualification of all personnel that visually inspect cleaned equipment would be an expected outcome.  

Implementation of a visual-inspection qualification program at a site presents some logistical complications. Qualification of validation personnel for cleaning validation procedures is usually conducted for a small group and can be done in a laboratory setting. For qualification of all necessary personnel for visual inspection, however, it would be more practical to bring the visual testing to the personnel in a general meeting room or training area. A viewing station with the dried samples mounted for viewing displayed on a table or hung on a wall would be ideal.  


  Testing parameters for visual-inspection qualification should be based on the viewing parameters of cleaned equipment at a site. For equipment that is manually cleaned or cleaned in a parts washer, inspections are generally in the 1-2 ft range. The viewing angle is unrestricted, and the inspection is conducted under ambient light. For larger, stationary, CIP equipment, the viewing distance is increased; the viewing angle will be restricted, and the lighting level could be lower on the interior surfaces of the cleaned equipment. An evaluation of the site equipment and facility should drive the viewing distance, viewing angle, and lighting conditions of the viewing parameters for visual qualification. Suggested parameter guidelines include: < 10 feet viewing distance; > 30º viewing angle; and > 200 lux lighting level (2). 
  


The materials of construction (MOC) for the visual-inspection qualification should be the most prevalent MOC at the site, which in many cases will be stainless steel as shown in 

Other representative MOC can be included as deemed appropriate, and their viewing characteristics should be considered. The optimal viewing parameters for glass, for example, provide additional challenges for a visual-inspection qualification (3). Optimal viewing conditions for glass involve holding the glass and looking through it at a slightly offset angle from the light source. Other MOC such as Teflon, which make it much more difficult to discern residues, are not value added for visual-inspection qualification. These MOCs need to be addressed in a different format, such as cleanability. Concerns for visual inspection of MOC need to be addressed either experimentally (4) or during on-the-job training.  

The residues for visual-inspection qualification should include all products manufactured at the site. A subset of the site‘s product-portfolio residues can be used with justification based on experimental evidence of similarity of residue appearance. If available data show (5) that the VRL of the API is as low as that of the formulation,  then API residue samples, which are often easier to prepare, could be used for the qualification. The residues tested for the visual inspection qualification should be indicative that the qualified inspector will be able to detect residues on the manufacturing equipment during a visual inspection both after cleaning and again before manufacturing.

The residue levels for visual-inspection qualification should be based on the visible residue limits (VRL) of the APIs or products in the site’s manufacturing portfolio. At a minimum, the VRL must be established for all of the products manufactured at the site used for qualification. A more thorough evaluation would establish separate VRL for all products, APIs, excipients, and detergents used in manufacturing or cleaning at the site (5).


  There are several alternative approaches for qualification of personnel for visual inspection. The first and most obvious option is to present stainless-steel coupons spiked with a number (e.g., 10) of representative products at the VRL mixed in with an equal number of blank, unspiked coupons and presented in a random order for qualification as shown in 

 The number of products would depend on the site product portfolio, but ideally all products’ residues would be presented. The personnel would either see the residue on the spiked coupons or not see residue on the blank coupons. The advantage of this approach is that it is the most straight forward and presents spiked coupons and blanks in a pass-or-fail situation.

This approach, however, does not train personnel on the appearance of residues as their concentration nears the VRL. Personnel undergoing qualification could misidentify a spiked coupon as blank or a blank coupon as spiked. A variation on this approach would present the APIs as well as the products for situations where the API is solely involved in one or more of the manufacturing steps or where the site product portfolio is limited to only a few products. Another variation could include VRLs on additional MOC coupon types if this were deemed necessary. Finally, a site with a limited product portfolio could present multiple spiked coupons of the same product to complete the qualification array.

A second alternative would be to present spiked coupons in decreasing concentration to mimic a VRL determination. The spiked coupons would be mixed with blank coupons and randomly presented for qualification as shown in 

. This approach would give personnel an idea of what residues look like at higher concentrations and the pass-or-fail criterion could be based on the VRL of the product or the spiked coupon at the next highest level to the VRL. The number of coupons required would be much greater or the number of products tested would be limited. A variation on this approach would present the VRL coupons and the concentrations approximately 25% above the VRL or present the 25% higher concentration for qualification. This is a low-risk approach when the established VRL is significantly lower than the allowable residue limit (ARL) based on patient-safety concerns. 

This approach has been used to establish VRL levels (6).  Coupons were presented in both a serial order from high to low and in a random order for VRL determination. Data concluded that the order of presentation had no impact on the observer’s ability to discern the VRL. The observers in that study, however, had previous experience with VRL determinations.   

Using spike levels greater than the VRL for visual-inspection qualification, whether multiple or single level, is difficult to justify if the established VRLs are rugged. VRLs are established so that there is a level of confidence that all personnel will be able to see the VRL level. Using multiple residue levels for visual-inspection qualification clearly indicates a lack of confidence in the established VRLs or the ability of personnel to detect them.


    The logical acceptance criteria for visual-inspection qualification is that the trainee identifies all of the spiked coupons as visible and all of the blank coupons as blank. If a trainee misidentifies a coupon, either spiked or blank, should they necessarily fail the qualification? For a spiked coupon, a misidentified coupon would have to be considered as a qualification failure. For a blank coupon, a misidentified coupon would not necessarily have to be considered as a qualification failure. A blank coupon deemed visible is a mistake on the side of caution and could be tolerated. Identifying multiple blank coupons as visible could be problematic in that it might lead to unnecessary investigations into properly cleaned equipment being declared not visibly clean. The acceptance criteria for visual-inspection qualification could allow one or more blank coupons to be misidentified as visible. The acceptable number of allowable misidentified blanks (e.g., 0-3 of 10 blanks) would be decided at the site based on a risk assessment of the VRL ruggedness and its relation to the allowable safety cleaning limit. The greater the difference between the VRL and ARL levels, the greater the assurance one has that visually clean pharmaceutical manufacturing equipment is sufficiently clean and the lower the risk of a cleaning failure as a result of an inadequate visual inspection. 

Training for visual-inspection qualification


    Qualification for visual inspections of cleaned equipment is just one part of the training required to assure reliable, thorough visual inspection of cleaned pharmaceutical manufacturing equipment. As shown in

, adequate training should start with a review of the visual inspection and the visual-inspection qualification SOPs, which describe the process for inspection and documentation of cleaned equipment and the visual-inspection qualification process respectively. If available, equipment diagrams showing dimensions and swab locations with associated justification can be reviewed to familiarize trainees with the manufacturing equipment and problem areas for cleaning. Prior to qualification, training on VRL determination should consist of several examples of VRL determinations in order to acquaint personnel with the appearance of low levels of residues for cleaning. Training for VRLs on different MOCs should be included if there are multiple MOCs at the site and they are part of the qualification. If personnel are involved in determination of VRLs, then the VRL example review might not be necessary. A discussion of the relationship of the VRL to the cleaning limit or ARL and the relationship of the cleanability of the different residues from the various MOCs would impart an understanding of the confidence level in the cleaning procedure and the visual inspection. On-the-job training should consist of supervised inspection of the manufacturing equipment, including the hard-to-clean locations and those locations most likely to have product build-up, for each piece of cleaned equipment as identified for cleaning validation. The final step after training and qualification should consist of a monitored visual inspection of a cleaned piece of equipment, ensuring that the proper procedures are followed, a thorough visual inspection is conducted for the equipment, and the visual inspection is properly documented. 

Review   standard operating procedure (SOP) for the visual inspection of cleaned manufacturing   equipment

Review   SOP for qualification of personnel for the visual inspection of product contact   areas

Review   equipment diagrams showing hard-to-clean areas and areas of product build up

Review   visible residue limit (VRL) examples

Table I. Training for visual inspection qualification.


Qualification of personnel for visual inspection of cleaned pharmaceutical manufacturing equipment’s product-contact surfaces is a necessary complement to both a cleaning-validation program and the manufacturing operations at a site. Visual-inspection qualification is just one facet of an overall training program to assure that personnel are equipped to provide a consistent, thorough, and accurate evaluation of cleaned surfaces for ongoing pharmaceutical operations.  

 Title 211.67 (Government Printing Office, Washington, DC).
2. R. J. Forsyth and V. Van Nostrand, 

. 29 (10) 152-161 (2005).
3. R. J. Forsyth, K. Bader, and K. Jordan, 

 37 (10) 86-91 (2013).
4. R. J. Forsyth, K. Bader, and K. Jordan, “Cleanability of Pharmaceutical Soils from Different Materials of Construction,” in press.
5. R. J. Forsyth, 

 33 (3) 102-111 (2009).
6. R. J. Forsyth, 


  Richard Forsyth is a principal consultant with Forsyth Pharmaceutical Consulting, 907 Shamrock Ct, Royersford, PA 19468, tel. 484.535.1688, 

Different approaches for qualification of personnel for visual inspection of residues on equipment surfaces are reviewed.

Qualifying Personnel to Visually Inspect Cleaned Equipment

Validation or re-validation of a cleaning program requires two criteria to establish equipment cleanliness. The first criterion is that there can be no carryover that will have an adverse impact on the patient (1). Setting a health-based limit to assure patient safety can begin with the allowable daily exposure (ADE) of the API approach (2, 3), or with the 1/1000th of the therapeutic dose approach (1, 4). The health-based limit is not only specific for the API but also for the manufacturing equipment in the facility.   

The second criterion is that the equipment must be visually clean (5). Visually clean equipment can involve either a qualitative assessment or quantitative assessment using a visible residue limit (VRL), which is the level below which an API or formulation is not visible. VRLs have been established for use in clinical (6) and manufacturing (7) facilities. In Part I of this series, the ruggedness of the VRL approach was shown for hundreds of APIs, excipients, formulations, and detergents (8). In Part II, ruggedness was also demonstrated regarding the presentation of the coupons to the observers (9); however, to date, all VRL data has been generated using stainless-steel coupons. Because stainless steel comprises the vast majority of pharmaceutical manufacturing equipment product contact surfaces, it was the logical material of construction (MOC) on which to concentrate. 
  

Determining VRLs for other materials of construction has been a question of considerable interest. Swab recovery studies have shown that a common recovery factor can be developed for the vast majority of different materials of construction (10); however, it is intuitive that the VRL for a given soil will differ from stainless steel to clear glass to the white background of polytetrafluorethylene (Teflon, DuPont). There are a variety of materials of construction to be considered for VRLs and depending on the equipment configuration, an alternate material of construction could comprise the majority of the product contact surface area. Once the VRL is established for a variety of MOC coupon types, which VRL to use going forward is the question. A distinct VRL for each material of construction is too cumbersome to develop, maintain, and assure compliance. Using the highest established VRL for the range of materials of construction is overly conservative unless the material of construction with the highest VRL is also the primary component of the manufacturing equipment. The current study was conducted to generate data to provide a basis for addressing these issues.

Polytetrafluoroethylene   (Teflon, DuPont)

Polypropylene, silicone, latex rubber, ethylene propylene   diene monomer, neoprene


    The VRL study was conducted to determine visual limits for a variety of soils on a range of MOC coupons using the following parameters.

 lists multiple MOC coupon types, which are commonly used in pharmaceutical and biopharmaceutical manufacturing. A subset of coupon types was chosen as representative of the MOC coupon types. Stainless steel was chosen as representative of metal coupons; glass was chosen as representative of clear coupons; and polytetrafluorethylene (Teflon, DuPont) was chosen as the most difficult to see of the opaque coupons.  

Pharmaceutical soils included aspirin, caffeine, calcium carbonate, diphenhydramine, and ibuprofen tablets. The concentrations of the tablets are shown in 

 The tablets were initially dispersed in several millimeters of distilled water. The soils were accurately diluted with isopropanol to the approximate concentrations listed in

. Isopropanol was chosen as the spotting solvent because it spreads easily due to its low surface tension, resulting in residues of approximately the same area, and it also evaporates quickly.

The soils were deposited onto individual coupons at the various concentrations in a serial order. Isopropanol was deposited on one of the coupons to serve as a negative control. Either 100 µL or 200 µL of the suspension were spread on the coupons. The final residue areas, concentrations, and observations of the five soils are shown in 

For observation, the coupons were arranged first by soil and then sequentially by concentration on the three MOC coupon types. Observers independently viewed the coupons under well-defined, controlled conditions. The light level was between 350 lux to 400 lux. Data have shown that a light level of more than 200 lux lighting provides consistent results (6-8). Three observers viewed the coupons from a distance of 2 ft at a viewing angle of 40 º and determined the level of each soil that was visible on the MOC coupon. Changing viewing parameters did not significantly change the ability to see residue on stainless steel, but the ability to detect residue on both glass and polytetrafluorethylene (Teflon, DuPont) was greatly influenced by the viewing parameters. The optimal viewing parameters for glass were similar to stainless steel, but highly dependent on the background. Either dark or white backgrounds can make visual detection difficult. A medium, neutral color enhanced residue detection. Alternatively, looking through the glass with the light source behind and slightly offset as shown in

1 also afforded equivalent viewing parameters.

Optimal viewing conditions for glass are fairly restricted and need to be established for each facility. Residues on polytetrafluorethylene (Teflon, DuPont) are difficult to detect but viewing from a shallow angle as shown in 

 seemed to give the best chance of seeing the residue. The observers determined the VRL of each soil under optimal conditions on each material of construction as presented in 


The MOC coupons chosen for the study were seen as representative of a wide variety of materials. A subset was also chosen, rather than to attempt a comprehensive survey of materials of construction because the combination of soils and materials of construction are typically restricted to a single site. Implementation of this approach at a site should include all soils on all materials of construction employed at the site unless an abbreviated approach can be justified.

The target residue concentrations as shown in 

 were based on past experience with a wide variety of pharmaceutical soils dissolved or suspended in methanol on stainless steel (8). The low surface tension of isopropanol allowed the residues to spread out on the materials of construction. The resulting concentrations of the dried residues are shown in Table IV. The combination of soils, MOC coupons, and solvents should be assessed for each facility to ensure a uniform distribution of residues.

Observations of the residues on the different MOC coupons varied based on the observation parameters. Residues on stainless-steel coupons were visible at a light level of  > 200 lux, a viewing angle of  > 30 º, and a distance of < 10 ft (3 m). Observations of residues on glass coupons were more challenging. Residues were visible when the viewing angle was at 30 º with the coupons laying flat on the viewing surface. Residues were not as visible at other angles. Residues were also highly visible when the glass coupons were viewed looking through the coupons with the light source at a slight offset behind the coupon. Under the optimal viewing conditions, the VRL on glass is comparable with the VRL on stainless steel. Residues on polytetrafluorethylene (Teflon, DuPont) coupons were not visible at the highest levels, > 5 µg/cm2. The observed VRLs for all of the residues tested on the three materials of construction are listed in 

The authors evaluated a variety of materials of construction (MOCs) and found that visible residue limits (VRLs) were higher on some MOCs than on stainless steel. The optimal viewing conditions were dependent on the MOC and the viewing background. The risk of a cleaning failure due to visual failure for different MOCs can be mitigated or eliminated using complementary cleaning validation studies.

Ruggedness of Visible Residue Limits for Cleaning-Part III: Visible Residue Limits for Different Materials of Construction

Visual inspection is always a component of a cleaning-validation program, and routine visual inspections for equipment cleanliness are a crucial part of day-to-day operations in a pharmaceutical facility (21 

 211.67 (b)-6). Visible-residue limits (VRLs) can be established for the active pharmaceutical ingredients (APIs), excipients, and detergents processed in the facility. The VRL of the API is generally the greatest concern because the API is the most potent component of the formulation. If the VRLs are lower than the health-based and adulteration-based acceptable residue limits (ARLs) as determined by the company, then the VRL is a viable approach to assess the equipment cleaning in the facility (1). 

Sample preparation and viewing parameters for VRLs have been established for pilot-plant and commercial-manufacturing facilities in previous studies (1, 2). A solution or suspension of the API in methanol was applied at different concentrations to stainless-steel coupons, thus resulting in residues of uniform size. Studying viewing parameters, such as viewing distance, viewing angle, light intensity, residue composition, and observer subjectivity resulted in the optimal viewing conditions to detect visible residues. These viewing conditions in the pilot plant were set at 18 in., 30°, and > 200 lux, respectively. For commercial facilities with larger, fixed equipment, the viewing inspection parameters can be restricted. The limits for acceptable viewing conditions were determined to be ≤ 10 ft, ≥ 30°, and > 200 lux. A discussion of the applications of VRL use and the associated risks concluded that the potential for a cleaning failure was small when a well-controlled VRL program was employed (3–5).  

The subjectivity of the observers and the appearance of the dried residues remained as potential limitations to a VRL program. The original VRL work used a small group of four to six observers (1, 2). For subsequent work, a larger pool of observers determined the VRLs of APIs in development at one site. In addition, a study of VRL determinations of five APIs at multiple sites helped to address the issues of observer subjectivity as well as residue sample preparation to better define the ruggedness of VRLs for cleaning (6). 

The complete set of VRL data was examined for distribution and trends (6). The original VRL data set was compared with the subsequent data set and demonstrated improvements in the procedure and technique. Refining the testing range to lower concentrations improved the procedure. It resulted in more accurate VRLs and fewer in which the lowest spotted concentration was visible. The training of personnel in VRL appearance and detection both in the lab and in the field improved the technique of visual observation. The VRLs of the APIs, excipients, and formulations showed a correlation between the VRL of the API and its formulation. Appearance of the residues depends on the amount of API residue being spotted and the volume of spotting solvent, which translates to the concentration of the resulting residue. VRL residues can appear as a uniform residue at higher concentrations, or as a ring, which is typical of lower concentrations. Methanol is consistently used as the spotting solvent because its low surface tension allows it to spread to a uniform spot size and its high volatility allows it to dry quickly. Experience gained through ongoing equipment inspections and direct soiling of manufacturing equipment with test soils confirmed that potential residue on cleaned equipment would be similar in appearance to the experimental VRL residues. 

Despite the extensive ruggedness data generated, the following questions about the constant parameters of the VRL studies remain to be answered:   					

What is the effect of the material of construction (MOC) on VRL determination? Intuitively, the VRL would be MOC-dependent, but to what extent? Can MOC be grouped for VRL purposes?  

What is the effect of the preparation solvent? Solvents will dry differently based on volatility, and the presentation of the resulting residue could be affected. This difference could potentially form a uniform residue, as opposed to a nonuniform ring residue.  

What is the effect of drying residue under air versus nitrogen? Certain APIs degrade while air drying, but the degradation could be an artifact of the spotting solvent and not occur during normal use. This is probably more of a chemical-degradation issue rather than a physical-appearance issue.

What are the effects of less-than-optimal viewing conditions? VRLs were established under controlled laboratory conditions. Although equipment-inspection parameters were defined (≤ 10 ft, ≥ 30°, and > 200 lux), visual inspection of large, enclosed equipment (e.g., tanks) provides a special set of challenges. The surrounding surface compositions can influence the ability to detect a VRL, and the phenomena of this influence need to be determined.

These issues will be the subject of future work and will require significant resources in time, material, and data to arrive at meaningful conclusions. The question explored in this study was the most straightforward: whether the presentation of the residues to the observers affects the VRL determination. The original study design anticipated that the lower concentration residues would not be visible. For a high percentage of samples, however, the VRL was determined to be less than the lowest residue concentration spotted on the coupons. The consistent ability of observers to see the lowest spotted residue prompted the question of whether they saw the residue because they knew there was a residue present. This was a legitimate concern when applied to clean equipment inspection, where the expectation is that there would be no residue present. 

Determinations of VRLs consistently followed the same manner of presentation for the observers. The arrangement of the soiled coupons began with the ARL, which was the lower of either the health-based limit or the adulteration-based limit (4 µg/cm

 ). Residue levels decreased sequentially with a solvent blank as the last sample. The observers viewed all of the sample soils as a single group. For the majority of samples (133 of 200 = 67%), the lowest spotted residue was visible for the observers.  The VRL was reported as less than the lowest residue concentration. This report resulted in a refinement of the sample preparation. The updated residue preparation, as shown in Table I, targeted lower concentrations to determine the actual VRL and provide more accurate program data. With this refinement, the observers continued to visually detect the lowest residue limit in the majority of tested compounds. 

Table I: Residue target concentrations. 			

An alternative arrangement of the residue soils was considered to determine whether presenting the soiled coupons to the observers affected VRL determinations. This alternative arrangement consisted of a randomized presentation of several compounds at or near the determined VRL, including a number of blank coupons. The observers did not know beforehand the number of compounds tested or their concentrations, the number of soiled coupons, or the number of blanks in a 25 coupon array. A randomized coupon presentation is more scientifically justified and easier to defend.  

Table II: Compound visible-residue limits (VRLs) 			

A series of four previously studied compounds with established VRLs, listed in Table II, were diluted with methanol to sequentially lower concentrations. The coupons were prepared using 100 µL of each solution resulting in four residue levels. The target concentrations were the four lowest concentrations shown in Table I: 20 µg, 10 µg, 5 µg, and 1 µg. One residue level was spotted per coupon. The spotted samples dried as elliptical residues. The resulting residue concentrations were calculated using the two elliptical radii in Table III based on the amount of residue spotted and the area of the resulting residue.  

The coupons were arranged in a random order as shown in Table IV and Figure 1. Sixteen sample coupons and four solventblank coupons were prepared. In addition, five blank coupons brought the total matrix to 25 coupons in a five-by-five array.  

Table IV: Random coupon identification grid. 			

The viewing parameters had been established previously: viewing distance was 18 in., viewing angle was 30°, and ambient light intensity was > 200 lux (1). Eight observers participated in the study. The observers viewed the coupon array separately from one another to avoid influencing their individual choices. The results for the random determinations are presented in Table V. 

Figure 1: Random coupon presentation. 			

After the observations were completed for the random coupon presentation, the residues were ordered sequentially, two observers were brought back to view the coupons, and their observations were recorded (see Table V). The sequential presentation was a confirmation for the previously established VRLs because the residue preparations were, in some cases, much lower than the reference VRL and because every residue preparation is slightly different based on the amount of compound weighed and the area of the resulting residue. 

The results of the VRL determinations for both the random and sequential presentations are shown in Table VI. The random coupon presentation provided comparable results to the sequential coupon presentation. For both the sequentially and the randomly presented coupons, the experimentally determined VRLs were lower than the previously determined VRLs for three of the compounds and higher for the fourth.  The lower VRLs resulted from spotting lower concentrations than in the initial VRL determination. The initial determinations were deemed acceptable because they were sufficiently lower than the swab limit or ARL (2). The sample preparation used for the more recent VRL determinations resulted in lower overall VRLs and a more rugged data set (6).   

Table VI: Visible-residue limit (VRL) determination. 			

Aside from the presentation of the coupons, the other significant difference was the number of blank coupons presented.  The VRL determination using the random coupon presentation involved a greater number of blank coupons (i.e., nine) than did the sequential coupon presentation (i.e., four). It was felt that the additional blank coupons would increase the physical separation of the soiled coupons, limit direct side-by-side comparisons of the soiled coupons, and enable a more independent assessment of each of the individual soiled coupons.   

Figure 2: Sequential coupon presentation. 			

The consistent results obtained using either method of coupon presentation answered a long-standing question. The sequential coupon presentation raised a concern that the decreasing residue concentrations and the close proximity of adjacent residues might lead observers to see residues where they might not ordinarily have identified a visible residue. 

Because the two methods of coupon presentation result in the same VRL, which way should one present coupons for VRL determinations? The sequential coupon presentation offers marginal advantages in the following areas.   					

It provides ease of setup and recording. The random coupon presentation requires slightly more paperwork with its matrix approach.  

It is easier to do one or more multiple compounds/residues at a time. The random approach is more suited to multiple determinations.  

It makes more efficient use of coupons, because the random approach will use additional coupons to fill in the square matrix as necessary.  

As noted above, the primary advantage of the random presentation was to increase the physical separation of the soiled coupons and limit direct side-by-side comparisons.  

To ensure rugged, reproducible results, however, the observers must be thoroughly trained. It is always emphasized during training that the VRL is a physical property of the residue and that the ability to see every spotted residue is not an expectation.  Observers are then more likely to report what they see rather than what they think they are expected to see. Therefore, the optimal coupon presentation depends on the level of training for the coupon preparation and the observers.  For newly trained personnel, the random coupon presentation might be appropriate, and the sequential coupon presentation might be more appropriate for more experienced personnel. 

The presentation order of the coupons appears to have no effect on the determination of VRLs. Both a sequential presentation from high to low concentration and a random presentation resulted in the same conclusions for VRL levels, thus confirming the ruggedness of the VRL determination. 

is a senior consultant with Hyde Engineering + Consulting, 6260 Lookout Rd., Suite 120, Boulder, CO 80301, tel. 303.530.4526, fax 303.581.0839, 

Submitted: Oct. 1, 2010. Accepted: Dec. 1, 2010. 

 4. R.J. Forsyth, J.L. Hartman, and V. Van Nostrand, 

The author challenges current detection methodologies.

Ruggedness of Visible-Residue Limits for Cleaning (Part II)

The concepts of "clean-hold time" and "dirty-hold time" have been part of cleaning validation since its inception. 

 is generally considered to be the time between the completion of cleaning and the initiation of the subsequent manufacturing operation. 

 can begin when the clean equipment is initially soiled, but more often is defined as the time between the end of manufacturing and the beginning of the cleaning process. Intuitively, it makes sense to be concerned about both hold times. Dirty equipment is harder to clean the longer the hold time, and clean equipment has a greater chance of becoming soiled as hold time increases.  

Guide to Inspection of Validation of Cleaning Processes

, the US Food and Drug Administration considers identifying and controlling the length of time between the end of processing and each cleaning step to be critical elements of the cleaning processes (1). FDA also expects pharmaceutical companies to demonstrate that routine cleaning and storage of equipment does not allow for microbial proliferation. The European Union expects companies to provide a validation master plan with clearly defined and documented validation program elements (2). Health Canada looks for companies to describe the interval between the end of production and the beginning of the cleaning procedures as well timeframes and conditions for the storage of clean equipment that do not allow for microbial proliferation (3). Finally, the Pharmaceutical Inspection Convention and Pharmaceutical Inspection Co-operation Scheme (PIC/S) guideline looks for documentation of both dirty- and clean-hold times (4). The general practice among industry is to routinely document and track equipment-hold times to ensure ongoing compliance.  

Although regulatory agencies expect manufacturers to document and address hold times, they do not describe a process for establishing hold times. In this validation study, a dirty-hold time was established but ongoing implications were not examined (5). Several articles define both clean- and dirty-hold times and how to establish them but do not mention a strategy to guide the experiments (6, 7). A more recent article, which referred to hold-time studies as "the lost parameter for cleaning validation," explored several issues associated with hold-time studies (8). Issues included storage conditions, test locations, testing methodology, and the length of hold-time studies.  

The concern with clean-hold times is that clean equipment will not stay clean indefinitely despite using appropriate storage conditions. Holding soiled equipment makes it more difficult to remove pharmaceutical soil and allows biological contamination to proliferate. To address these concerns, the author extended clean-hold time testing for more than 2 yrs and extended dirty-hold time studies for up to 9 days. After identifying clean- and dirty-hold time, ongoing control of the hold times became difficult. Every time a piece of equipment is used, the operator needs to confirm and document that the actual clean-hold time does not exceed the established clean-hold time. And before washing a piece of equipment, the washer needs to confirm and document that the actual dirty-hold time does not exceed the established dirty-hold time.  

This study suggests that if clean- and dirty-hold time issues are addressed during the validation study that the severity of exceeding the established hold times diminishes to a near-acceptable level. 

 Table I: Dry granulation equipment train-dirty-hold validation (Acceptable residue limit [ARL] = 100 Âµg/swab) 

As part of the cleaning-validation study in a pilot plant (5), soiled equipment was held after processing for an extended period of time before cleaning. The hold times for the three validation trials held ranged from 2 h–217 h or 9 days. Data from the validation study including dirty-hold times are shown in Tables I, II, and III. The results include data from a typical dry-granulation equipment train and a wet-granulation equipment train. The majority of the data (187 of 231 swabs) showed no detectable residue. All results were far below the acceptable residue limit (ARL) of 100 µg/swab. The tests showed that over the time span examined, the dirty-hold time had no discernable impact on the ability of the cleaning process to effectively remove the soil from the manufacturing equipment. 

Table II: Wet granulation equipment train-dirty-hold validation (Acceptable residue limit [ARL] = 100 Âµg/swab) 

The clean-hold time validation study was conducted independently. After cleaning, the equipment was wiped or sprayed with alcohol to remove residual water, dried, and covered to prevent any dust or particulate accumulation. The validation study consisted of three trials; one trial extended the clean-hold time. The clean-hold times for the three trials ranged from same-day cleaning to a hold time of 2 yrs and 5 mo. Storage conditions included both the clean-equipment hold area in the pilot plant and a storage room outside the pilot plant but in the same building. Data from the clean-hold time study are shown in Tables IV, V, and VI. The majority of the data (128 of 180 swabs) showed no detectable bioburden and all results were far below the ARL of 100 colony forming units (cfu)/swab. The results include data from a typical dry-granulation equipment train and a wet granulation equipment train. The results demonstrate that bioburden was not present immediately after cleaning and was not a cause for concern during storage of properly cleaned, dried, and covered equipment. 

Cleaning-validation studies have established equipment dirty-hold times and clean-hold times for pharmaceutical manufacturing equipment. The ongoing expectation is that equipment cleaning documentation verifies compliance with the validated hold times. A conservative approach uses either the established time for each group of equipment, which makes recordkeeping difficult, or the shortest established extended hold time for all equipment. Using this approach, the dirty-hold time is limited to 7 days and the clean-hold time to several weeks. A more aggressive approach uses the longest hold-time data. This gives a maximum dirty-hold time of 9 days and a clean-hold time of more than 2 yrs. 

Table IV: Dry granulation equipment train-clean-hold validation (Acceptable residue limit [ARL] = 100 cfu/swab) 

An examination of the clean-hold time data supports the more aggressive approach. The data were consistent for both the wet- and dry-granulation equipment. The average bioburden level for the 180 samples taken was 1.1 cfu/swab. There were 128 samples with no detectable bioburden and only nine with a bioburden greater than 10 cfu/swab. Although the majority of samples were taken shortly after cleaning, samples were taken at 1, 2, 5, and 8 mo and at 2 yrs, 5 mo with no discernable increase in bioburden. With a bioburden limit of 100 cfu/swab, clean-hold time is not an issue for cleaned equipment that is dried, covered, and stored appropriately. 

Table V: Wet granulation equipment train-clean-hold validation  (Acceptable residue limit [ARL] = 100 cfu/swab) 

The dirty-hold-time study needed to answer two questions. Does the soil become harder to clean the longer it sits, and what is the possibility of microbial proliferation on soiled equipment? Soils can be more difficult to clean when they are wet and allowed to dry onto the surface, or when the soil is hygroscopic and transforms into a pasty material or subsequently dries. A high-shear granulator is the only equipment that carries out wet granulation at the conclusion of unit operation. The dirty-hold time for the high-shear granulator (196 h) was lengthy enough to allow any wet material to dry. The controlled humidity of the pilot plant prevented any moisture uptake by residual granulation. All other equipment in the validation studies resulted in a dry granulation at the conclusion of unit operation. Microbial proliferation was not a realistic possibility, which was corroborated by the clean-hold time data. 

Subsequent to the validation studies, the gross cleaning of the equipment, including scraping and vacuuming the equipment was shifted from the equipment-cleaning process to the manufacturing process, which effectively shortened dirty-hold times. Because of environmental considerations for residue disposal, equipment operators scrape and vacuum accumulated residue from equipment surfaces. Operators then wipe equipment surfaces with alcohol to remove as much of the residue as possible to minimize the amount of residue discharge to the municipal sewer system. An example of a typical soiled equipment surface prepared for cleaning is shown in Figures 1 and 2. The steps taken for environmental concerns effectively shorten the dirty-hold time. The alcohol wipe dries within minutes, leaving no wet material to dry and become harder to clean. The dry soiled surfaces do not have sufficient water activity to support microbial proliferation. There is no sufficient residue remaining for hygroscopic residues to be a concern. The dirty-hold time data, which measured cleaning effectiveness out to 9 days, demonstrated a worst-case scenario for the pilot plant facility. The dirty-hold time is not of significant concern for soiled equipment awaiting cleaning. 

Figure 1. High-shear granulator prepared for cleaning. (FIGURES ARE COURTESY OF THE AUTHOR) 

Under the operating conditions tested as part of the cleaning validation studies, the clean- and dirty-hold times have little impact on the ongoing operations of the pilot-plant facility. In addition, routine verification of adherence to these parameters adds little value to a firm's ability to produce quality formulations. The risk, therefore, tied to 

 monitoring hold times should be low for validated cleaning and storage conditions. 

Figure 2. Granulator exit chute prepared for cleaning. 

If clean- and dirty-equipment hold times are established during validation and maintained under properly defined and controlled conditions, the need to monitor clean- or dirty-hold times is not necessary. Avoiding these steps can result in savings of time and resources as well as potential regulatory exposure.  

 is an associate director of worldwide GMP quality with Merck & Co., Inc, WP53C-307, West Point, PA. 19486, tel. 215.652.7462, fax 215.652.7106, 

Submitted: Nov. 16, 2007.  Accepted: Dec. 20, 2007. 

, Division of Field Investigations, Office of Regional Operations, Office of Regulatory Affairs (Rockville, MD), July 1993. 

Annex 15, European Union Guide to Good Manufacturing Practice, 

Working Party on Control of Medicines and Inspections, European Commission (Brussels, Belgium), July 2001. 

Cleaning Validation Guidelines (Guide-0028), D

rug GMP Inspection Unit (Ottawa, Ontario) May 2000. 

 4. "Recommendations on Validation Master Plan Installation and Operational Qualification; Non-Sterile Process Validation; and Cleaning Validation," in proceedings of the PIC/S (PIC/S, July 2004). 

 5. R. J. Forsyth and D. Haynes, "Cleaning Validation in a Pharmaceutical Research Facility," 

 6. J. A. Morales Sanchez, "Equipment Cleaning Validation Within a Multi-Product Manufacturing Facility," 

 7. A. H. Mollah, "Risk-Based Cleaning Validation in Biopharmaceutical API Manufacturing," 

 8. T. Fugate, "Hold Time Studies: A Lost Parameter for Cleaning Validation," 

Regulatory agencies expect companies to establish and monitor clean equipment- and dirty equipment-hold times for manufacturing equipment as part of their cleaning validation program.

Equipment Hold-Time for Cleaning Validation

A well run cleaning-validation program requires a significant amount of planning and resources. Planning takes into account the size, configuration, and complexity of the manufacturing equipment; the physical properties of the soils encountered, which directly affect the cleaning procedure used; the detergent to clean the equipment; the type of swab or rinse sampling to capture residue levels; the analytical test methods to determine residue levels; the periodic monitoring of the system to ensure ongoing compliance; change control to address new residues and equipment; appropriate documentation; and training for personnel cleaning equipment and performing validation challenges. Required resources include equipment downtime for the validation, raw materials for the formulations tested, analytical instrumentation for analysis, detergents for cleaning, solvents for testing, and personnel to perform the validation. 

The entire cleaning-validation program and its execution depend directly on the acceptable residue limit (ARL) for the formulation residue. The active pharmaceutical ingredient (API) residue is monitored because it is the most phamacologically active component of the formulation. The ARL established for a program must be scientifically justified on the basis of the needs and capabilities of the manufacturing facility. In its 

Guide to Inspection of Validation of Cleaning Processes 

(1), the US Food and Drug Administration stated that residue limits should be logical, practical, achievable, and verifiable. The agency did not intend to set acceptance limits for validating cleaning processes. One of the examples cited as a possible residue limit used in industry, however, was 10 ppm of carryover into the subsequent batch manufactured. 

The purpose of cleaning validation is to prevent the cross-contamination of a drug formulation. The primary concerns of cross-contamination are an evaluation of the therapeutic-dose carryover or the toxicity of the potential contaminant. Any contaminant is undesirable, but one with a pharmacologic or toxicological effect is far more serious. The Food, Drug, and Cosmetic Act (2) states: "A drug ... shall be deemed to be adulterated if it consists in whole or in part of any filthy, putrid, or decomposed substance," that is, something that will cause an adverse pharmacological effect. This definition supports the pharmacological and toxicological concerns. 

If, however, the amount of a residue is below the level at which it would have an unintended, adverse health effect, what is the allowable level from an adulteration standpoint?  Should a health-based limit be the only limit for equipment cleaning? Should the analytical-method detection limit be the standard (3)? Or, if an intermediate adulteration limit exists, what rationale determines that level? In the past, analytical methodology had limited sensitivity, making health-based and adulteration-based contaminations essentially equivalent. The increased sensitivity of analytical methodology seemingly has created a contradictory situation. Modern analytical detection limits are far lower than the pharmacological levels of drugs, thus creating a divergence between the previously equivalent health-based and adulteration definitions. 

A logical residue limit would be one that demonstrates no pharmacological or toxicological effect, without regard to analytical sensitivity. This would indicate that residue levels can be as high or as low as the health-based limit will allow. This approach, however, would allow equipment to be visually dirty for relatively safe residues, which indicates an inadequate cleaning procedure. A logical residue limit also should leave the equipment visually clean. Setting residue limits any lower than the health-based and visible levels does not appear to be necessary or logical and adds no additional value to the cleaning process. 

Several cleaning-validation programs use the dual health-based–adulteration-based criterion (4–6). Evaluations based on toxicity, tablet weight, number of doses administered, swab recovery, swab area or equipment surface area, and batch size determined the ARLs from both an adulteration-based and health-based perspective. The lower of the two limits was the designated ARL for the formulation and the equipment. 

The cleaning-validation program in our pilot-plant facility calculated ARLs for both the health-based and adulteration-based criteria and used the lower of the two (7). The dynamic nature of the pilot plant and the drug-development process necessitated regular re-evaluation of the ARL for each API. Each API required a health-based evaluation, but the majority of development compounds had such low toxicity that their adulteration limits were lower. A proposed alternative to the constant re-evaluation of adulteration limits was to use a constant adulteration limit of 100 μg/25 cm

 . This technique would streamline the cleaning process and minimize potential errors without compromising quality or safety. 

To implement an adulteration limit, it must be lower than the associated health-based ARL. The adulteration limit would be lower at the level at which compounds are not likely to be potent, highly toxic, or carcinogenic. A corresponding allowable daily intake (ADI) for this category of material is 100 μg/day (0.1 mg/day) (8). 

The calculation for the health-based ARL with an ADI of 0.1 mg/day includes: 

in which ADI is the allowable daily intake for the compound, SSA is the shared product-contact surface areas of the manufacturing equipment train, and recovery is the percentage of spiked material recovered for assay. 

Table I shows the health-based ARLs with associated parameters for an ADI of 0.1 mg/day, tablet weight from 0.1–1.5 g and maximum daily dose from 1–10 tablets. The number of tablets per batch ranged from 266–10,000 (small) to 3600–160,000 (medium) to 46,666–1,000,000 (large), based on batch sizes of 0.4–1 kg (small), 5.4–16 kg (medium), and 70–100 kg (large), respectively. It was assumed that the next batch was manufactured in equipment with the same SSA. 

Table I: Calculated health-based acceptable residue limit (Î¼g/swab).

The shaded portions of the small, medium, and large batch ranges in Table I fell below the proposed limit of 100 μg/swab (4 μg/cm

 ). The low end of each range assumed the smallest batch size, the largest tablet weight (1500 mg), and the highest number of tablets dosed (10). 

In the pilot plants, about 5% of manufactured batches fell below the 100 μg/swab (4 μg/cm

 ) limit. The batches that fell below the 4 μg/cm

  limit were typically for clinical studies with large tablet sizes (>1000 mg), multiple-tablet doses (>6 tablets/dose) or small batch sizes (<500 g). Small batch sizes generally are for first-in-man studies or preclinical and Phase I studies. These clinical-trial programs are dosed on small populations to establish dose levels.  

  limit for compounds with ADIs >100 μg/day was small, based on the site data. Also, of the 1225 swab samples taken in support of cleaning validation, none failed the ARL for the compound tested, greater than 98% of the swabs were below 1 μg/cm

 , and more than 99.5% were below 4 μg/cm

Finally, a continuing program for monitoring cleaning effectiveness using visible residue limits (VRL) was conducted. Of the manufactured batches that fell below the 100 μg/swab (4 μg/cm

 ) limit, the highest VRL was 1.23 μg/cm

 , which is well below the health-based limit. Therefore, for compounds with ADIs >100 μg/day, it is extremely unlikely that the adulteration limit selected will be greater than the health-based limit. 

The adulteration limit was used when it was lower than the health-based limit. For development compounds in the pilot plant (7), the adulteration limit originally was calculated using the following equation: 			

in which UAL was the upper acceptance limit; SSA the shared surface area, MBS the minimum batch size for the equipment train, and recovery the fraction of spiked material recovered for assay. The UAL of 10 μg/g (10 ppm) cited by FDA (1) was used in various cleaning-validation programs (3, 9, 10). The SSA was the combined product-contact surface areas of the manufacturing equipment train. The MBS provided the most conservative limit because any residue would be most concentrated in the subsequent batch. The swab area of 25 cm

  was used widely (3, 7, 11, 12) in industry. 

Calculation of an allowable adulteration level was a logical cleaning limit for a pilot plant but in the long term proved to be impractical. The number of factors that went into the pilot-plant production schedule, the drug-development formulations, and the residue determination made an adulteration assessment a constantly changing number. 

The pilot plant manufactured varied formulations of numerous compounds. The programs in the pilot plant increased with new compounds and decreased as programs ceased development or were transferred to commercial manufacturing. Schedulers, formulators, equipment cleaners, analytical chemists, and quality personnel were involved. The number of programs and personnel along with the associated ARL calculations, documentation, and communication made it difficult to maintain a consistent, compliant program. 

 The number of new compounds entering the pilot plant was significantly greater than the number of new compounds entering a commercial manufacturing facility. These new programs had to be included in the overall cleaning-assessment program. Validating a new compound required significant analytical method development and validation. In addition, the small, early-phase manufacturing equipment was in great demand, and extended downtime for cleaning validation support was problematic.  

 The manufacturing schedule in the pilot plant was variable. Equipment was scheduled for use several weeks in advance, but other programs sometimes took priority. Even knowing the subsequent product was no guarantee that a particular formulation was the same as the previous one manufactured for the product. Calculating an ARL based on the subsequent product manufactured in the equipment was problematic. 

Current equipment train versus subsequent equipment train.

 The equipment train was the order in which equipment was used to manufacture a formulation. Blending, granulation, roller compaction, drying, and tablet pressing were examples of unit operations that together manufactured a clinical formulation. The ARL calculation for the equipment train assumed that the same train was used for the subsequent product. This almost never was the case in a pilot plant, which made the value of the ARL limited. An alternative ARL calculation considered each individual piece of equipment without regard to the manufacturing train. This type of ARL consideration became exceedingly cumbersome without adding increased value to the ARL process. 

An adulteration limit of 100 ?g/25cm? (4 ?g/cm?) was proposed for pilot-plant facilities. The dynamic changes in equipment, formulation, and residue determination made implementation of a constantly changing, calculated adulteration limit impractical. A single adulteration limit was simpler to communicate and document, making compliance achievable. The limit would be used only after it was determined to be lower than a health-based evaluation and a visual-cleanliness assessment.