Joanne Ratcliff, PhD, is communications project manager, Laboratory Weighing, Mettler Toledo GmbH, Joanne.Ratcliff@mt.com.

Joanne Ratcliff, PhD

Capsule filling is common in preclinical and clinical studies. Companies are increasingly developing cytotoxic and potent compounds; containment of these substances is, therefore, a primary safety concern for laboratory managers. As the API dosed into capsules are typically not fully characterized at this stage, they must be treated as high-potency to protect the researchers handling them, because any spillage or exposure presents a potential safety risk.

	Often, only a limited quantity of the drug substance is available. When working with a new chemical entity, where the synthesis program may run concurrently with the early dosing studies, early batches may be of the order of several grams, with perhaps a gram or less available for development work. At this phase, the drug is expensive and precious, so it is important to avoid wasting any.

	Depending on the nature of the drug and test subject, new pharmaceuticals are often administered in gelatine capsules. The fill weight of each capsule must be accurately calculated and prepared according to the test subject’s weight. This preparation involves manually weighing highly potent, hazardous substances precisely with a spatula. Manual capsule filling, however, is tricky and challenging, especially with small capsules.

	Manual filling is usually performed manually when the sample series are too small for filling machines or different amounts are required per capsule, which is not easy to automate. Manual filling can be slow and tedious, especially if tens, hundreds, or even thousands of capsules have to be prepared each day.

	There are various solutions to overcome the manual filling challenges:

		Low-cost capsule boards are an extremely fast method of filling capsules, but have some drawbacks. Capsules cannot be filled with pure API because it would deliver too much API per capsule; hence, an excipient must be used. As segregation of powders cannot be controlled, homogeneous-proof samples are required and different formulations per capsule are not possible. Filling is achieved by volume, which is not highly reproducible, and capsule weights cannot be checked afterwards.

		Automated filling machines are a higher-throughput approach, but typically come at a high investment. Usually requiring at least a kilogram scale of material to run a batch, they are not flexible enough to fill different amounts per capsule. Additionally, these systems require time-consuming commitments of maintenance and cleaning between batches to prevent cross-contamination and ensure safety.

		Semi-automated capsule filling solutions bridge the gap between the manual and high-throughput machines. These flexible systems are usually compact and affordable, ideally suited for small batch capsule filling and accurately dosing different target amounts to each capsule gravimetrically (e.g., Quantos, Mettler Toledo GmbH).

	Reduce time and enhance safety using automation

 In a GMP lab, a validated filling system provides reduced labor time compared to manual filling. A technician may be capable of manually preparing 85-125 capsules per day at 3 mg target weights (technician dependent), whereas a semi-automated system produces 60 capsules per hour. Although the manual estimate depends on the standard operating procedure (SOP), a manual fill in a GMP lab would also require the eyes of two technicians: one to tare the balance, fill the capsule, and record the final fill weight; and the other present to verify each of these steps. Whereas, using a validated filling system requires only one operator to perform the task. Additionally, the tare and fill weights can be captured electronically and stored and/or printed automatically, which reduces the labor time associated with data recording/transcription.

 By using neat API in capsule, formulation development time can be reduced by simply evaluating the compatibility between the capsule shell and the API, instead of investigating excipient compatibility and fully formulating a dosage form. Analytical method development time can also be reduced because no specificity needs to be qualified, as no interfering excipients are present. Thus, the analytical method for the drug substance can suffice for the drug product.

	Typically, release testing is performed on all incoming materials and final dosage forms before release to the clinical side. Using neat API in capsule, the initial release determines the purity and potency of the API, which minimizes the release testing and allows substances to get to the clinic faster.

Minimize cleaning and cross contamination

. In setting up a typical fully automated encapsulation machine, there are a number of product contact parts that have to be cleaned and verified by swabbing after dosing to determine residual API left on the instrument. However, semi-automated filling systems are much simpler to clean, because no substance comes into contact with any other part of the system other than the dosing head and the sample changer, which is easily detached for cleaning. The rest of the system is considered non-product contact and thus needs no additional cleaning verification. Cross-contamination risk is eliminated, as separate dosing heads are used for each substance.

. With high-potency substances, semi-automated capsule filling offers significant safety benefits. Potential exposure is reduced using a self-contained dosing unit. The drug substance is stored in a standard jar or vial with a dispensing head screwed on top, protecting the analyst from the drug, and the substance from the environment. At this phase, when working with new chemical entities that can cost thousands of dollars per gram, it is important to avoid any substance wastage. Weighing small quantities such as 1-5 mg, manually with a spatula, can result in significant loss or spillage. Having a system that accurately dispenses exactly the required amount, without wasting anything is, therefore, beneficial.

	When referring to this article, please cite it as M. Greene and J. Ratcliff, “Overcoming the Challenges of Capsule Filling in Preclinical and Clinical Studies" sidebar to “Key Considerations in Capsule Filling," 

Articles

The authors discuss the challenges of capsule filling in preclinical and clinical studies.

Overcoming the Challenges of Capsule Filling in Preclinical and Clinical Studies

	A measurement of any kind is affected by the errors and uncertainties that exist in that measurement process. During calibration, the performance of an instrument is assessed and its limitations originating from errors and uncertainties are made evident; this is the essential foundation for achieving accurate measurement results.


	Calibration is more than just comparing a “standard” number with a displayed value on the balance. There is a calibration process that relates to the combination of uncertainties achieved when a balance weigh cell is deviated from its rest position. Calibration establishes the relationship between the displayed value and a standard or accepted true value. The values must fall within an assigned measurement uncertainty range (1, 2).

	A calibration is meaningless without the measurement uncertainty for that specific instrument. Only once the instrument uncertainty has been established, and providing that the number is within the required process tolerance, can it be classed as an accurate calibration.
	Measurement uncertainty is derived from known scientific methodology. It is not something that can be decided by a company or committee. There is an internationally correct and recognized way of calculating measurement uncertainty, described in the Guide to the Expression of Uncertainty of Measurement (GUM) (3).

	It is crucial that the weights used in routine testing are certified as traceable and that the certification is current. If the weight is out of certification, it is no longer guaranteed to give the maximum permissible error (MPE) that is expected.

Why is measurement uncertainty important?


	A modern electronic weigh cell works differently than a traditional mechanical balance. In an electronic weigh cell, the relationship between what is displayed on the screen and the errors involved is not linear. The current approach to metrology, however, is often based on history and familiarity, rather than a scientific study of the process. Traditional methods of balance testing need to be updated and replaced with scientifically meaningful tests, which include an estimation of measurement uncertainty. A knowledge of measurement uncertainty can be used to develop a streamlined, robust, and meaningful testing regime that meets scientific requirements but doesn’t take up several hours every week.

What contributes to total measurement uncertainty?


	The total measurement uncertainty is shown in Figure 1by the black line (U_tot). The significant factors that contribute to measurement uncertainty across the weighing range (4) are described as follows.

. Repeatability, also known as precision, is the largest single contributor to the total measurement uncertainty. At the lower end of the weighing range, the total measurement uncertainty detected is almost entirely due to the repeatability, shown by the yellow line (U_RP) in 

. The magnitude of the repeatability uncertainty completely obscures the chance to measure any other components in this range.

. The eccentricity or cornerload error is the error associated with not placing the weight in the center of the weigh pan. The eccentricity is only significant, and therefore detectable, at the higher end of the weighing range, as shown by the green line (U_EC) in Figure 1.

. Nonlinearity is the error due to the nonlinear behavior of the balance upon increasing the load on the weighing pan. It is not a dominant influence at any point on the weighing range. At the low end of the weighing range, the nonlinearity is superimposed by repeatability uncertainty. At the high end, it is dominated by sensitivity. In fact, at no point on the weighing range does it account for more than 0.1% of the total measurement uncertainty that can be detected. Nonlinearity is significant for the manufacturer because it provides information about the mechanical operation of the balance. For people who have worked for a long time in the pharmaceutical industry, where it may be normal to carry out linearity checks daily, it may come as a surprise to learn that these tests are not as significant as previously thought.

. Sensitivity (i.e., systematic deviation) is the key parameter (besides repeatability) that should be assessed periodically. At the higher end of the weighing range, the sensitivity and eccentricity become the dominant contributors to the overall measurement uncertainty. The high end of the weighing range is thus the ideal place to carry out these routine tests. 

 clearly shows that the sensitivity component of uncertainty (pink line, U_SE) is a completely horizontal line, which means it can be safely assumed that if the sensitivity measurement is performed at the high end of the weighing range, the result represents the whole of the nominal capacity of the balance, providing that the weigh cell is working correctly. Incidentally, if the weigh cell is not working correctly, a test carried out at the high end of the weighing range (as near to 100% of the nominal capacity of the balance) on a daily or regular basis will usually indicate any problems with the weigh cell immediately.


	A manufacturer or service provider will test the four significant components of measurement uncertainty when performing a calibration. These measurements are reflected on a calibration certificate. It is also expected that the balance user or internal metrology department will measure some of these contributors during routine balance testing operations.

	Good Weighing Practice (GWP), Mettler Toledo’s science-based standard for lifecycle management of weighing instruments, provides a strategy for reducing measurement errors and ensuring accurate weighing results. Based primarily on the user’s weighing requirements and prevailing weighing risks, GWP guides users on how to optimize routine testing procedures and how to avoid unnecessary or erroneous testing (4). GWP specifies which of the following tests should be carried out during routine testing.

. Perform (typically) 10 replicate weighings under the same conditions, using the same methodology, to give a statistically significant weighing sequence, according to the GUM (3). Calculate the standard deviation (s), which is the repeatability of the instrument.

Eccentricity test (i.e., cornerload error)

. Place a weight in the center of the weigh pan and zero the balance. Move the weight out to the corners of the weigh pan and take the readings. With a round weighing pan, the protocol is no different. The aim is to compare the difference between the extremities of the weigh pan to the center. Depending on the weighing process, this test can be omitted by the user.

Nonlinearity (i.e., error of indication) test

. Nonlinearity is not very significant at any point in the weighing range, so it is perfectly valid to omit this from the user routine testing regime. This test can be performed by the external service technician during the annual calibration or preventive maintenance visit. It is acceptable to perform a nonlinearity test only one or two times per year, even for a heavily used microbalance or analytical balance. Although it doesn’t need to be measured daily or frequently by the user, it does need to be included in the measurement uncertainty calculation, as per the GUM (3).

. This test is sometimes referred to as the highest “error of indication” test point. The aim is to measure the error of indication by placing a single weight on the balance and comparing it with a standard value. For accuracy, this test must be done at or close to the top of the nominal working range of the balance. Below that, increasingly lower uncertainty due to sensitivity can actually be detected. At the very low end, with very small weights, there is almost no sensitivity uncertainty detectable at all. At this point, the repeatability (i.e., precision of the balance) becomes the completely dominant factor.

	Although there are other contributors to uncertainty, such as external influences, the advantage of modern electronic weigh cell technology is that most of those uncertainties are included in the repeatability of the balance.


	Once the four uncertainty components have been determined during the full calibration by the manufacturer or service provider, the correct way to calculate the total measurement uncertainty (i.e., “given uncertainty budget”) for any balance or scale, according to metrology guidelines, is a two-step calculation. First combine the individual components to calculate the so-called standard uncertainty (u) for the instrument by using a root-sum-square method, as shown in the simplified model in 

 are the uncertainties due, respectively, to repeatability, eccentricity, nonlinearity, and sensitivity.

	Next, expand the uncertainty using standard scientific practices. For an expansion factor of k=2, which can be quite frequently applied, multiply the equation by 2 to give a 95.5% confidence level in the result (3).


	According to GWP, only two weights are required for a user to perform regular routine testing of their balance (4). The larger weight at 100% or close to the nominal capacity of the balance is used to perform the sensitivity test. The smaller weight (5% of the nominal weighing capacity) is used to perform the repeatability test.

	Linearity testing does require more than two weights. If a service provider performs the linearity testing as part of the annual calibration or preventative maintenance visit, however, then there is no scientific requirement for the user to check linearity more frequently.


	According to the laws of metrology, there is no traceable calibration without a statement of measurement uncertainty. Traditional balance testing should be replaced with scientifically meaningful test points. Testing at multiple points on the weighing range every day can take a lot of time, effort, and resources. In addition, the test points may not even be relevant if the metrology behind the testing is not considered. An understanding of the basic principles of balance and scale properties, such as measurement uncertainty, enables the user to achieve a qualified weighing process.

”, white paper no. 30260955 (May 2015),  accessed Feb. 29, 2016.
	2. K. Fritsch and I. Ciesniewski, NCSLI Measure: 

. 10 (3) 56-65 (September 2015).
	3. BIPM, Evaluation of measurement data-Guide to the expression of uncertainty in measurement, JCGM 100:2008, GUM 1995 with minor correction, first ed. (Sèvres, France, September 2008).
	4. K. Fritsch, NCSLI Measure: 


	Ian Ciesniewski, PhD, is technical director, and Joanne Ratcliff, PhD, is communications project manager, both at laboratory Weighing, Mettler Toledo.

:
	When referring to this article, please cite it as I. Ciesniewski and J. Ratcliff, "Understanding Measurement Uncertainty in Weighing," 

Understanding of the basic principles of balance and scale enables a user to achieve a qualified weighing process.

Scientific Approach Ensures Accurate Weighing Results

A program for calibration and routine testing of weighing instruments ensures accurate results.

Understanding Measurement Uncertainty in Weighing

Data integrity is a major regulatory topic in GMP-regulated laboratories. The problem is widespread, as cases of non-compliance have also been observed in laboratories regulated by good laboratory practice (GLP) and good clinical practice (GCP), not just GMP. Non-compliances from the European Medicines Agency (EMA) or warning letters from FDA show examples from companies in the United States, Canada, the United Kingdom, and Italy, as well as China and India. So, it is not just a problem for Asia-it is a global issue.

	The non-compliances are not confined to falsification and fraud. In fact, in the majority of labs, the main data integrity issues concern poor data management, which account for 95% of non-compliance cases; only 5% are a result of falsification or fraud. Problems arise from basic errors such as relying on paper as raw data and failing to protect electronic records, rather than deliberate manipulation of data. It is the latter, however, that gets the major headlines. In July 2014, FDA issued a stern warning that data integrity was a key focus of its enforcement efforts (1).


	In January 2015, the UK Medicines and Healthcare products Regulatory Agency (MHRA) went further and issued 

 (revised in March 2015) (2). This guidance consists of descriptions, definitions, and expectations based around those definitions, which include raw data, original records, file structures, and audit trail. The regulatory expectations presented in this guidance are useful. However, the definitions are simply presented as a shopping list; a diagram explaining and linking key definitions would be more beneficial.

	The guidance presents data integrity as the extent to which all data are “complete, consistent, and accurate” throughout the data lifecycle, which covers the period from data acquisition through to interpretation, reporting, and archiving and then destruction after the record retention period. There are similarities in the US regulations; a 20-year-old FDA definition of data integrity describes the degree to which a collection of data is complete, consistent, and accurate (3).

	In European GMP regulations, documentation constitutes a key part of quality assurance and, therefore, compliance with GMP (4). An organization must have good documentation, follow standard operating procedures (SOPs), and demonstrate compliance with the applicable regulations. Several requirements focus on data integrity for computerized systems (5). If critical data are entered into a data system, a second check is required, which can either be a second person or can be automated using the computer system itself.

	In the US, the regulations for laboratory records focus on the concept of complete data (6).

	A review of data integrity warning letters reveals several citations for failure to have complete data including a failure to have a complete procedure (7), a failure to fully document the work that is carried out (8), or being selective in reporting data (e.g., using test samples to “check” if an instrument is working correctly) (9). Complete data includes the actual observation, which can be visual or by computerized system. Contextual metadata, which puts the data or result in context, is also required. Examples of metadata include operator ID, units of measurement, sample information, identity, batch number, instrument suitability, and readiness. Audit trail events are also part of the metadata. If a hybrid system or a fully electronic system is used, FDA and European regulatory agencies require companies to review and evaluate audit trail events to see if data have been manipulated without authorization.

	FDA guidance comprises a list of commonly asked questions and answers that are crucial for maintaining data integrity (10). Detailed explanations are given for:

		Why paper records from a hybrid system should not be defined as raw data-instead it should be the underlying electronic records; Although the reasoning focuses on chromatography, it is applicable to any computerized system.

		Why sharing of user identities in a computerized system is not allowed-as it makes it impossible to attribute the work carried out to a single individual.

		Why actual samples should not be used as system suitability tests to see whether a batch passes or not. FDA warning letters reveal many citations for this transgression.


	The criteria for data integrity are defined by the acronyms ALCOA and ALCOA+. ALCOA, which stands for attributable, legible, contemporaneous, original, and accurate, was developed by an FDA GMP inspector in the late 1980s. ALCOA has been used in many areas that are regulated both by FDA and other regulatory agencies worldwide. In 2010, EMA published a paper on electronic source data for clinical records, in which another four requirements relating to electronic data were added: complete, consistent, enduring, and available (11). The Good Automated Manufacturing Practice (GAMP) Data Integrity Special Interest Group (SIG) now refers to ALCOA+, which includes the nine attributes or criteria for data integrity (see 


	In the past, an inspector would review piles of paper; to view a computer system, he would be shown print-outs of the screen. Now, the focus is on the computerized systems and the electronic records within; the paper output is secondary. Inspectors will focus on the electronic records, looking at how they were generated and manipulated within the application. In the light of these changes, consideration needs to be given to the person who will manage the system during an inspection. How is the system configured to protect the electronic records? Are electronic signatures being used in the application, ensuring that the configuration of the application is documented and reflects the settings within the software?

	Annex 11 now requires audit trail entries to be reviewed, and FDA considers these entries as part of the complete data. Many findings of non-compliance during inspection have been discovered by looking at audit trail entries, therefore, an approach to reviewing audit trail events is needed. Citations have noted when audit trails were been turned off, the audit trail had not been reviewed, or user identities were shared, which is not allowed under the regulations. Additional citations can be found in the September 2014 issue of 


	The 10 compliance commandments for computerized laboratory systems described in 

Where should the electronic data transfer begin?


	Let’s consider preparation of standards by way of example. In an analytical lab, standards are usually prepared using an analytical balance. The actual weight is typically printed on a strip printer and pasted into a lab journal. Afterwards, the standards are widely used for analytical methods, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), titration, etc. Data management and documentation for analytical instruments are usually managed by dedicated software or a laboratory information management system (LIMS). This procedure is currently allowed by regulatory bodies, which state that print-outs representing original data for simple devices (such as balances) are acceptable (2) but is not the case for more complex devices. Nevertheless, it is important that reference standards are accurate and traceable because they represent the starting point of many analyses. Warning letters have cited “no details available on the preparation of standards or solutions, especially of analytical reference standards” (13, 14). Independent of process, it is important to ensure that all the data are available.

	This then begs the question: Where should the electronic transfer begin? In the process described above, there is a gap in the data transfer between the “simple instrument” (the balance) and the “complex instrument” (e.g., the HPLC). Clearly, this is not recommended because it introduces an additional level of risk; it is obvious why no gaps should occur.

	Capturing the data at the point of origin and transferring the data electronically throughout the whole workflow is a much lower risk approach and reduces the risk of errors during the early stages of a process, giving additional confidence in the compliance of a workflow or laboratory.


	The next question then becomes:  What data need to be transferred? It is essential to associate results with metadata to build context around the values collected. Although integrating even a simple instrument can be tricky, the advantages of an integrated solution are obvious. When electronic data transfer starts from the beginning of the process, each piece of information needs to be input only once for it to be available throughout the whole system. This allows seamless movement of data and other information from the start of a process to the end, without the need for manual effort, such as manual transcription, creating an efficient work environment.

	This transfer of data is achievable using a laboratory execution system (LES), such as LabX, which enables a variety of instruments to be directly connected (balances, titrators, density meters, refractometers, thermal analysis instruments, and pH meters). Useful features such as SOP-user guidance on the instrument terminal, automatic results capture in a database, and real-time data access support traceability of data and compliance with the GAMP data integrity criteria in ALCOA+.

	As regulators continue to tighten their inspection approaches, it is crucial for managers and scientists in regulated GXP laboratories to understand these criteria for data integrity and to assess and improve laboratory data management processes to ensure compliance with current regulations. Only after all these points have been addressed can data integrity truly be achieved.

Current Regulatory/Inspection Issues Related to Supply Chain

,” Food and Drug Law Institute (FDLI), Conference Understanding cGMPS-What Attorneys Need to Know, Washington DC, July 15, 2014.
	2. MHRA, 

Glossary of Computer System Software Development Terminology

EudraLex, The Rules Governing Medicinal Products in the European Union

 Volume 4, Good Manufacturing Practice, Chapter 4 Documentation (June 2011).
	5. European Commission,

, Volume 4, Good Manufacturing Practice, Annex 11 Computerised Systems (January 2011).
	6. US Electronic 

FDA Warning Letter to Ipca Laboratories Ltd

FDA Warning Letter to Micro Laboratories Ltd.

Questions and Answers on Current Good Manufacturing Practices, Good Guidance Practices, Level 2 Guidance-Records and Reports

GCP Inspectors Working Group publication, Reflection paper on expectations for electronic source data and data transcribed to electronic data collection tools in clinical trials

 (London, June 2010).
	12. R.D. McDowall, 

FDA Warning Letter to RPG Life Sciences Ltd.


	When referring to this article, please cite as B. McDowall and J. Ratcliff, "How Important is Data Integrity to Regulatory Bodies?" 

Data integrity is a widespread, global problem that must be addressed.

How Important is Data Integrity to Regulatory Bodies?

 General Chapters <41> Balances and <1251> Weighing on an Analytical Balance became official on Dec. 1, 2013 (1, 2).  These revisions aim to ensure weighing accuracy and eliminate unnecessary overtesting for US pharmaceutical manufacturers and suppliers. The chapters attempt to simplify previous descriptions and reflect current state-of-the-art weighing practices. Revisions include modified balance test procedures, which focus on the determination of minimum weight, and the execution of routine testing.

The new requirements of General Chapter <41> are mandatory. The revised chapter now states that accurate weighing must be performed using a calibrated balance. It also details a relatively demanding balance assessment, describing accuracy and repeatability tests with new acceptance limits. This applies for balances used to weigh analytes for quantitative measures. 

For accuracy testing, use of a test weight of 5–100% of the balance capacity is now applicable. Accuracy, defined by 

 as the systematic error, must be determined at higher loads close to the balance capacity (i.e., largest systematic error), as it cannot be detected reliably below 5%. Hence, accuracy testing below 5% is no longer allowed (see 

In contrast, repeatability testing and minimum-weight determination should be carried out using a small weight below 5% of the balance capacity (see 

). In this lower range, the repeatability is the dominant source of error and is virtually independent of the test weight. With higher weights (i.e., above 5%), the repeatability is a weak function of the test weight and so the repeatability will increase, leading to higher minimum weight values.

For more information on balance testing, a video tutorial can be viewed at: www.mt.com/lab-usp-tutorial. 

Advisory Chapter <1251> provides additional clarification and extends the scope to any balance used for an analytical procedure. These major revisions focus on balance qualification and operation. Installation qualification (IQ), operational qualification (OQ), and performance qualification (PQ) recommendations are given. PQ, for example, should be carried out using a risk-based approach. 

For the first time, the term “minimum weight” is officially introduced in a pharmaceutical compendium. This requirement is clearly applied to the sample weight, not including the tare vessel. Every balance has an individual minimum weight, depending on the type and performance of the load cell, the location, and the environmental conditions. The minimum weight of every balance should be periodically assessed for conformance. During a webinar in December 2013, it was encouraging to note that the majority of balance users (75% of those surveyed) are already familiar with the term minimum weight (3). 

It is also important to note that USP recommends how to establish the minimum weight for applications outside of 

 <41>, with the phrase “If not subject to the requirements of General Chapter <41>, the minimum weight value may vary depending on the required weighing tolerance and the specific use of the balance” (1).

Chapter <1251> goes on to provide practical recommendations for the installation qualification and operation of balances. Amongst others, it describes several environmental factors that can influence the performance of a balance, such as air currents (drafts), temperature variations (e.g., direct sunlight), vibrations, and electrostatic effects. These factors can all affect the minimum weight of a balance at a specific time. 

Crucially, weighing net samples sufficiently above the minimum weight is recommended to take balance performance fluctuations into account. The implication is that a safety factor should be used when weighing, as shown in Figure 3. The use of a safety factor ensures that the smallest net weight is sufficiently larger than the minimum weight determined at a particular time by a particular person.

Applying a safety factor minimizes the risk of out-of-calibration, out-of- specification (OOS) or out-of-tolerance (OOT) results. The safety factor is the quotient of the smallest net weight and the experimentally determined minimum weight. It accounts for environmental influences and variations in operators, samples, and statistical factors. The safety factor applied should depend on the risk. It should be higher for more critical applications and unstable environments. 

Another consequence of the USP revisions is that a daily balance check, typical in the pharmaceutical industry, is no longer a requirement. Instead, the type and frequency of balance checks should be determined by the risk and process tolerance of the application. The more critical the impact of an incorrect result, the more testing should be carried out, to reduce the risk of OOS or OOT results. In any case, it should contain at least a regular calibration with determination of measurement uncertainty and periodic sensitivity and repeatability testing. Performing the right tests at the right intervals will ensure quality results. During a webinar in December 2013, a majority of balance users (77% of those surveyed) admitted to still carrying out balance checks daily or before every use (3). This result indicates that many companies could potentially benefit from eliminating unnecessary testing, which would bring significant time and cost savings. 

Common questions about the USP revisions 


Since the USP announced these revisions, some questions have arisen. 

Q: The USP chapters focus primarily on analytical balances. Are these revisions applicable to balances in a production or manufacturing environment?

A: The scope of USP is quality control of drugs. If the procedure referred to in a USP monograph requires materials to be ‘accurately’ weighed, a balance that weighs ‘accurately’ (meeting 0.10% requirements for repeatability and accuracy) is needed. If not, the balance repeatability and accuracy should meet other defined weighing tolerances commensurate with the requirements of the application. This aspect does not apply to production scales. However, production scales can also have a critical impact on the quality of drugs and thus need to meet GMP requirements. GMP requires scales to be consistently accurate and to be periodically calibrated and tested. Thus, the same scientific principles of managing weighing equipment--summarized in GWP (Good Weighing Practice, Mettler Toledo)--apply for production and quality control. The difference is that USP <41> explicitly requires a weighing tolerance of 0.10%, whereas the weighing tolerance in production can be chosen and defined based on specific quality and process requirements. Most pharmaceutical companies typically use a weighing tolerance limit between 0.1% and 2%.  

For all applications, weighing should be carried out using a calibrated balance that meets the requirements for repeatability and accuracy.

Q: What does USP mean when they say that balance checks with external weights can be replaced partially using automatic or manually triggered adjustment by means of built-in weights?

A: With some limitations, the internal test can be considered as an external sensitivity test. It detects systematic deviations and adjusts for it. However, since the internal weights are not traceable, an external, traceable weight must be used periodically. In practice, ‘partially’ means that if the internal test is performed on a daily basis, the external frequency can be extended to once a week or once a month, for example. It is recommended to activate the in-built automatic adjustment function using the internal weights and to program (or trigger manually) the balance for a daily adjustment. Depending on the risk of the application, further measures may be recommended. 

Q: Do we need to establish the minimum weight for each balance or can we just set a nominal minimum weight for all five-place balances?

A: Every balance has an individual minimum weight, depending on the type and performance of the load cell, the location and the environmental conditions. This means that 10 different balances of an identical model may have 10 different minimum weights. In theory, it is possible to set the smallest net weight to a relatively high threshold to cover a family of identical balances. However, this would eventually mean that weighing range is lost with those balances that perform better, and weighing more material could mean wasted sample and, therefore, higher costs. Nevertheless, if the smallest net weight for a series of instruments is set to 50 mg, for example, then the minimum weight of every balance must still be periodically assessed for conformance. 

Q: What is a safety factor and how is it determined?

) is the quotient of the smallest net weight and the determined minimum weight; it accounts for environmental influences and variations in operators, samples, and statistical factors. The safety factor depends on the risk. It should be higher for more critical applications and unstable environments. We would recommend measuring the current, actual safety factor through a GWP Verification and then defining it based on the results and the risk analysis. 

Commercially available programs, like Mettler Toledo’s Good Weighing Practice, can help pharmaceutical manufacturers and suppliers to comply with the new USP guidelines by putting the guidelines into practice in a structured and effective way. Services can, for example, perform risk assessments and provide test methods and frequencies based on specific risks. 

 <41>, “Balances,” Second supplement to 

(US Pharmacopeial Convention, Rockville, MD, June 1, 2013).
  2. 	

<1251>, “Weighing on an Analytical Balance,” Second supplement to 

 (US Pharmacopeial Convention, Rockville, MD, June 1, 2013). 
3.	G. Martin, M. Huber, and J. Ratcliff, “Ensuring USP Compliance with Revised Chapters on Weighing,” webinar (Dec. 3, 2013).


Joanne Ratcliff, PhD, is communications project manager for Laboratory & Weighing Technologies, Joanne.Ratcliff@mt.com, and Martin Huber, PhD, is head of the GWP competence center, Martin.Huber@mt.com, both at Mettler Toledo.

The latest revisions to the USP General Chapters <41> Balances and <1251> Weighing on an Analytical Balance aim to ensure weighing accuracy and eliminate unnecessary overtesting by simplifying previous descriptions and reflecting current state-of-the-art weighing practices.

Complying with Revised Weighing Guidelines

Working safely with potent compounds presents challenges for the pharmaceutical industry because exposure to minute quantities could potentially cause health effects. Typically, an isolator would be the preferred containment technology for working with the most potent (occupational exposure band five [OEB 5]) compounds but it has drawbacks in terms of cost, space, efficiency, and ergonomics. The authors describe the advantages of using an automated powder dispensing system in a ventilated balance enclosure (VBE) for efficient handling and effective containment of potent compounds. A review of the data proves that air and surface contamination is well within the acceptable limits, demonstrating the applicability of the automated powder dispensing unit in a VBE for weighing potent compounds in the pharmaceutical industry.

In recent years, pharmaceutical companies have increasingly begun to work with potent compounds (i.e., compounds that are very active pharmacologically, with efficacy at sub-milligram doses). These compounds allow patients to take smaller doses and potentially experience fewer side effects. While this property is advantageous for the patient, it presents a greater risk to the health of analytical chemists working with these compounds because exposure to very small quantities has the potential to cause health effects. In some cases, the quantity of potent compound that can lead to health effects can be extremely small, being practically invisible in air or on work surfaces, which makes containment of these compounds in the workplace especially challenging. The list of potent compounds of interest to the pharmaceutical industry includes hormones, steroids, and many oncology drugs. These compounds have airborne occupational exposure limits (OEL) ≤ 10 µg/m

 as an eight-hour time-weighted average (1). For handling these compounds in the laboratory, a classification system is used to assign materials into a series of health hazard categories, or occupational exposure bands (OEB), of increasing severity based upon their inherent pharmacological and toxicological properties. This classification system helps companies identify risks associated with handling the compounds and provides guidance on how to manage them (2). While no official industry standard exists around the banding of compounds, companies typically utilize OEB systems with four to six categories (1). Each health hazard category corresponds to a predefined strategy known to provide the necessary degree of exposure control to protect employees and the environment. 

To support research and development as well as manufacturing of potent compounds, several contract manufacturers have made significant investments to build facilities to control exposure to potent compounds (3). Merck & Co., like other companies, has been developing potent compounds. Merck’s most potent compounds, known as OEB 5 compounds, typically require an isolator for dispensing milligram to gram quantities to maintain airborne levels below 1 µg/m

 and surface contamination below 10 µg/100 cm

Occupational    exposure limits (OEL) (µg/m3)

Good laboratory/ manufacturing  practices (GLP/GMP).  LEV may be needed.  No special    containment.

GLP/GMP.  LEV may be   needed. No special  containment.

Virtually no open    handling. Closed  systems   and/or  controlled by LEV, hoods or   HEPA-filtered ventilated enclosures designed for personnel  protection. 

No open handling. Closed systems and/or controlled by LEV,   hoods or HEPA filtered ventilated enclosures designed for personnel  protection.

No open handling. High containment required.


Working safely with these potent compounds presents   challenges. Employers are required to minimize the exposure risk by following the “hierarchy of controls.” Since substitution is not an option when developing or manufacturing potent drugs, engineering controls are required to be used as the primary control. The preferred containment technology is often an isolator that maintains exposures below applicable limits. Using an isolator for dispensing and weighing small quantities of these compounds, however, presents space, ergonomic, efficiency, and cost challenges for an analytical 
laboratory. Merck needed a simple solution to allow analytical chemistry researchers to work in a laboratory environment with OEB 5 compounds. The workflow needed to be safe, simple, efficient, and accurate enough to allow precision weighing while maintaining cGMP compliance.


Merck’s analytical laboratory originally invested in a semi-automated powder dispensing unit (Mettler Toledo) to address an increasing demand for routine weighing of nonpotent compounds. The system, however, subsequently proved to be an effective solution for handling potent compounds as well (see 

It consisted of an enclosed semiautomated dispensing unit attached to a regular analytical balance. The compound is sealed in a vial with a dosing head attached to the top of the container. The dosing head is inserted into the unit, and the balance doors are closed before dispensing takes place. Dispensing the compound from a sealed container reduces the risk of airborne contamination. Each dosing head contains a radio-frequency-identification (RFID) chip to enable identification and tracking of the compound, providing process security by eliminating the possibility of selecting or dispensing the wrong substance. The dispensing system is able to accurately weigh compounds from 1 mg to 5 g with a 2% variance and dispenses the required amount of material into a container that is securely located on the balance. Once the desired weight has been dispensed, the researcher can remove the container and place another one on the balance for the next weighing step. Alternatively, a 30-position autosampler can be added to automate the change of target container, which enables up to 30 weighing operations to take place without any user intervention. It is also possible to link a solvent dispensing module, which accurately adds the desired weight of solvent into the target container based on the actual amount of solid dispensed to achieve a desired concentration. This method is an even more precise way to prepare analytical solutions. Compared to conventional manual dispensing, the automated process can be as much as 20 times faster. 

A key benefit of automated dispensing is that it reduces user exposure by eliminating the handling of the substance with a spatula and minimizing the risk of spillage. It also reduces the manual actions required by the user, by eliminating the need for repeated opening of the balance door and transferring the compound from the main container to the secondary container to achieve the desired weight. 

The automated dispensing system was situated within a high-efficiency particulate air (HEPA)-filtered ventilated balance enclosure (VBE) (Pharmaceutical Containment Technologies [PCT]). The VBE has features key to effective containment such as rounded airfoils around the entire face, a waste chute to minimize researcher movement in and out of the face, safe-change HEPA filtration, and a flow alarm to ensure the face velocity does not drop below 60 fpm (0.3 m/s). The laboratory initially used this equipment to weigh less potent, OEB 3 and OEB 4 compounds, a task that the device performed remarkably well. A question was raised as to whether the capability of the unit could be expanded to handle the safe and efficient dispensing of OEB 5 compounds. After several discussions between Merck Global Safety and the Environment and Mettler Toledo, an experimental evaluation plan was created to assess the ability of the system to reduce airborne and particulate surface contamination during weighing of OEB 5 compounds. As part of the evaluation, OEB 5 materials were provided to the analytical laboratory in containers compatible with the dosing heads as historical air and surface contamination data indicated manual subdivision by analytical chemists in a VBE would not maintain airborne and surface contamination levels below applicable limits for some OEB 5 compounds.


  Verification sampling was performed to validate the equipment containment. Personal protective equipment (PPE) worn during the sampling included safety glasses, a disposable laboratory coat, disposable sleeves, and double nitrile gloves. Air and surface samples were collected during the dispensing of 2 g of naproxen sodium, and subsequent cleaning and PPE removal.

Naproxen sodium, a nonsteroidal anti-inflammatory drug, was used because it is recognized by the International Society of Pharmaceutical Engineers (ISPE) as a rigorous challenge agent and a suitable surrogate for assessing containment of potent compounds (4). The sampling protocol included cleaning of the VBE, containers, balance, and the removal of outer gloves and sleeves within the VBE given that proper technique during these activities is crucial to containment and the prevention of surface contamination. Six iterations of the dispensing task were performed, and air and surface samples were collected during each iteration to demonstrate that the controls and the procedures used by the researchers did, in fact, protect them. 

Results in micrograms per cubic meter of air (µg/m3)

Left side of VBE face 200 mm from opening

Right side of VBE face 200 mm from opening

In total, six personal air samples and 24 area air samples were collected. All samples collected were below the laboratory limit of detection and well below OELs for the OEB 5 compounds currently being handled in the laboratory (see

. Additionally, all wipe samples were below the surface contamination limits (see 

 Containment verification data: Surface sampling results. VBE is ventilated   balance enclosure. 

Results in micrograms per 100 centimeters square on the   surface (µg/100 cm2)


A review of the air and surface contamination data showed that exposures are low, generally nondetectable. It was concluded that researchers can safely utilize the automated dispensing system to dispense up to 2 g of OEB 5 compounds with OELs > 3 ng/m

, provided that the VBE is properly sited in the laboratory and use of the system is coupled with appropriate personal protective equipment, a written procedure, hands-on training on proper handling of potent compounds in a VBE, good handling practices, and an annual preventative maintenance program for both the dispensing system and the VBE. 

Automated powder dispensing offers an efficient combination of both strategies of containment and improved sample handling techniques. Combining the dosing head, a HEPA-filtered VBE, and good potent compound handling techniques can eliminate the need to use an isolator to precisely weigh OEB 5 compounds for analytical testing. An added benefit is that any researcher can undergo simple training and be qualified to operate the automated system, which also removes user variability from the process. Overall, the use of the automated dispensing system in a VBE affords accurate and reproducible weighing of potent compound while keeping researchers safe and protecting the laboratory environment from contamination.

, “Focus on CROs/CMOs” supplement, 29 (4) s20-23 (2011). 
  R. Harris, “Formulating High Potency Drugs,” 

 35 (12) 36-40 (2011). 
ISPE, Good Practice Guide: 

Assessing the Particulate Containment Performance of Pharmaceutical Equipment

, 2nd Edition (Tampa, Florida, May 2012) pp. 70.

George Hartford  is laboratory technician/inventory coordinator for labeled compounds in analytical chemistry, Patty Cheung  is associate principle scientist in analytical chemistry, Karen Whitaker  is senior specialist, Rahway Safety and the Environment, and Roy Helmy, PhD,  is director of analytical chemistry, all at Merck Research Laboratories, 126 East Lincoln Avenue, P.O. Box 2000, Rahway, NJ 07065-0900, USA; Joanne Ratcliff*, PhD,  is communication project manager, Laboratory & Weighing Technologies at Mettler Toledo AG, Im Langacher 44, P.O. Box LabTec, CH-8606 Greifensee, Switzerland, Joanne.Ratcliff@mt.com.  
*To whom all correspondance should be addressed. 

The advantages of using an automated powder dispensing system in a ventilated balance enclosure for efficient handling and effective containment of potent compounds are discussed.