Current activities of the USP Microbiology Expert Committee

The US Pharmacopeial Convention (USP) is a non-profit scientific organisation that develops standards for the identity, strength, quality and purity of drugs and their ingredients, which are published in the United States Pharmacopeia and National Formulary (USP–NF). Standards for drugs or drug ingredients are expressed in USP-NF monographs, general chapters and General Notices. A monograph is developed for a single article (e.g., drug substance, drug product, excipient), and a general chapter can apply across multiple articles. General chapters numbered above 1000 generally are informational, and contain no mandatory requirements unless specifically referenced in a monograph, General Notices, or a general chapter numbered below 1000. General chapters designated as below 1000 contain tests that are intended to apply to items recognised in USP or NF when called out in a monograph, General Notices or another applicable general chapter. USP general chapters may also be required by the US Food and Drug Administration (FDA) in addition to the role of USP standards in US law as part of conformity to current good manufacturing practices (GMP). Applicable to drug substances and products marketed in the US, USP’s standards are also used in more than 140 countries.

Through its Microbiology Expert Committee (Microbiology EC), USP develops and revises general chapters for the advancement of pharmaceutical microbiology, consistent with the organisation’s mission of quality medicines, food ingredients and dietary supplements. The current Expert Committee consists of industry experts and consultants along with FDA liaisons¹.

The Microbiology EC is responsible for general chapters that address microbial assays and microbial control of processes and environments. Its responsibilities do not extend to drug or product monographs, which are handled by other USP Expert Committees, although the Microbiology EC does support the development of microbial requirements for all monographs via consultation with the relevant monograph Expert Committees. Monographs and informational general chapters on pharmaceutical waters are handled by a separate Expert Committee.

The USP Microbiology EC has an established Work Plan for each five-year cycle during which it operates. The Work Plan is intended to help meet USP’s standards-setting goals. Major initiatives in the current USP 2010-2015 cycle regarding microbiological contamination include sterilisation processes and sterility assurance.

Sterility assurance and sterilisation

While all products purported to be sterile have to meet the requirements of General Chapter <71> Sterility Tests, sterility assurance is achieved only by the use of validated robust sterilisation processes. USP’s current General Chapter <1211> Sterilisation and Sterility Assurance of Compendial Articles addresses principles of sterility assurance and provides information on various sterilisation processes. In response to stakeholder feedback that greater detail is needed to address specific sterilisation methods, USP initiated a two-stage revision approach more than two years ago. Phase 1 focused on the correction of outdated content, which was replaced with current information and became official in USP 33-NF 28 (2010). Phase 2 involves a significant rewrite of the general chapter. The initial focus of this second phase is on sterilisation, to be followed by content relevant to sterility assurance. In determining how to update the sterilisation material in the general chapter (which had its origins in the late 1980s), the Expert Committee decided to split the content. Information related to sterilisation was removed from the existing General Chapter <1211>, and in a future revision, <1211> will be renamed Sterility Assurance of Compendial Articles. The focus of the revised General Chapter <1211> will be limited to sterility assurance and include aseptic processing, environmental monitoring, a brief mention of sterility testing and parametric release.

A related result has been the development of a new series of general chapters (the <1229.x> series) dedicated to individual sterilisation processes, with an overarching General Chapter (<1229>) covering overall concepts of sterilisation. In the development and organisation of these general chapters, the Expert Committee has decided to develop one on depyrogenation separate from another on dry heat sterilisation, in alignment with current industry practices. Depyrogenation processes will be addressed in a manner similar to those for sterilisation processes, and this effort is just beginning. Moist heat sterilisation will be divided into hard goods (direct contact approach) and aqueous liquids. Gas and vapour sterilisation will be addressed in separate general chapters.

To date, 12 general chapters that will provide valuable information and guidance on distinct methods of sterilisation have been planned, and currently four of these (first four in the list below) have already been approved for inclusion in USP-NF:

<1229> Sterilisation of Compendial Articles

<1229.1> Steam Sterilisation by Direct Contact

<1229.2> Moist Heat Sterilisation of Aqueous Liquids

<1229.3> Bioburden Monitoring

<1229.4> Sterilising Filtration of Liquids

<1229.5> Biological Indicators for Sterilisation

<1229.6> Liquid Phase Sterilisation

<1229.7> Gaseous Sterilisation

<1229.8> Dry Heat Sterilisation

<1229.9> Physicochemical Integrators and Indicators for Sterilisation

<1229.10> Radiation Sterilisation

<1229.11> Vapour Phase Sterilisation

Several others will be proposed in 2013, in Pharmacopeial Forum2 (PF)—USP’s free access, online journal for public comment on developing and revised standards. Highlights of some of the proposed general chapters are described below.

Although many steam sterilisation approaches related to hard goods are relevant to aqueous liquids, <1229.1> Steam Sterilisation by Direct Contact and <1229.2> Moist Heat Sterilisation of Aqueous Liquids have been written separately for greater clarity and to distinguish between the two. For example, when using the direct contact approach, overkill is the method of choice because overprocessing of parts or hard goods is usually not a concern. On the other hand, when developing sterilisation processes for liquid-filled containers, one can consider overkill as a first choice, but that decision will depend on the impact of the cycle on the fluids and container attributes. If the impact is too high, then alternatives to overkill cycles such as a bioburden-biological indicator approach may be developed. This general chapter also makes it clear that liquids other than finished products – such as laboratory and production media and bio-waste, and potentially some intermediates – also need appropriately developed sterilisation cycles.

The proposed general chapter on sterilisation by filtration describes how filtration is a retentive, non-destructive process relative to the microbial cell. Due to the non-destructive nature of the methodology, critical factors that can impact retention of microorganisms are conditions of filtration, characteristics of the filter and bioburden. A good understanding of these parameters will enhance the potential for successful retention.

General Chapter <1229.10> Radiation Sterilisation is not meant to repeat what is already in the ANSI/AAMI/ ISO 11137 standards. However, because of the importance of determining radiation dose, the general chapter will briefly discuss dose setting according to ANSI/AAMI/ISO standards. This is the only commonly accepted sterilisation method that does not require biological indicators for validation, due to the accuracy of dose measurement and its extensive correlation to microbial destruction. It is important to understand the bioload or bioburden of the material being irradiated.

The use of vaporised chemical agents for sterilisation and decontamination is common practice, especially in isolators used in manufacturing. Currently, the technology of vapour sterilisation suggests that two phases occur concurrently – a gas phase and a liquid phase. Kill rates for each phase appear to be quite different. Also, vapour conditions are probably not homogenous or uniform at all locations and may change during the process. Because of this uncertainty of conditions, the microbial destruction efficacy and consistency are difficult to ensure, and accurate D-value determination may be challenging.

This general chapter discusses bioburden control and monitoring as they relate to sterilisation in particular. Since an understanding of bioburden is so crucial to appropriate sterilisation design, this chapter will enhance understanding of the key elements in detection and identification of microorganisms with regard to survival, population and patient risk.

The intent of depyrogenation is very different from that of sterilisation. Thus, understanding and developing methods intended for depyrogenation have been separated into the <1228.x> series of general chapters.

Another major consideration for manufacturers with regard to microbial presence is contamination control. Keeping pace with changes in regulations and technologies, General Chapter <1116> Microbiological Control and Monitoring of Aseptic Processing Environments has recently undergone a major revision and became official in 2012. By changing the focus from evaluation of clean rooms to key guidelines that support sterile pharmaceutical processing environments, revised General Chapter <1116> addresses ways to help eliminate factors that support microbial growth, particularly those introduced as a result of human contact. Guidelines in the general chapter as well as monitoring parameters given for microbiological evaluation should be applied only to clean rooms, restricted-access barrier systems (RABS) and isolators used for aseptic processing. Changes to <1116> include clarification of limitations of counting methods used in microbiological evaluation, including sampling, recovery, data tracking and trend analysis. The use of microbial recovery frequency provides a more practical and useful concept for indicating that an environment is in a state of ‘control’.

The general chapter provides an improved description of microbiological incubation conditions relative to intended recovery (e.g., typical temperature and time, modification for slow growers). The general chapter also gives guidelines on the establishment of sampling plans and sites, microbiological sampling methods, contamination recovery rates and other important microbiological control parameters.

Bioburden control

In the arena of bioburden control for nonsterile pharmaceutical products, very little information is available in either the pharmacopoeias or regulatory guidance documents. Clearly the quality of raw materials, the surrounding environment during manufacture and personnel conducting quality control activities are just some of the factors that can contribute to the bioburden of a product. A draft proposed General Chapter <1115> Bioburden Control of Nonsterile Drug Substances and Products, which will be available for public comment in PF in 2013, outlines a risk-based approach to control potential contamination in non-sterile product manufacturing. It is important to understand that the manufacture and management of microbiological content of nonsterile products are distinctly different from what is required for sterile products. Therefore, the contamination recovery rates defined in <1116> Microbiological Control and Monitoring of Aseptic Processing Environments are not intended for nonsterile environments. By looking at specific factors that may affect product quality and patient safety and considering the best ways of dealing with them, the manufacturer can then identify the risk associated with a product and apply appropriate methods for bioburden control.

The general chapter also clarifies that although environmental contamination is by no means the most significant cause of nonsterile product recalls or contamination events, environmental monitoring can be a useful component in the overall microbiological process control program.

Replacing microbial assays with rapid methods

Conventional microbiology tests found in the pharmacopoeias, such as sterility tests, rely on the demonstration of microbial growth. Limitations of these tests include their low sensitivity as well their time and labour-intensive nature. Certain cytotherapy or regenerative medicine products and radio pharmaceuticals are administered to patients prior to results from sterility testing. A more rapid result test would be very beneficial in such instances. USP is seeking to identify new referee tests or procedures based on modern methods that can detect and enumerate microorganisms in a more rapid and sensitive manner. Objectives for such test method development are that the method has to have broad application, required instrumentation or supplies cannot be single sourced or patented and the method should be applicable in any lab.

Protocols will be developed to conduct proof-of-concept studies to demonstrate the reliability and suitability of the proposed methods. Based on these studies, a general chapter will be developed and published in PF for public comments.

USP is also currently in the process of updating General Chapter <1223> Validation of Alternative Microbiological Methods as guidelines for users interested in validating microbiological methods, including those based on modern technologies.

References

1. USP Microbiology Expert Committee 2010-2015: James Akers (Chair), James Agalloco, Dilip Ashtekar, Anthony Cundell, Dennis Guilfoyle (FDA), Rajesh Gupta (FDA), David Hussong (FDA), Karen McCullough Russell Madsen, Randa Melham (FDA), Jianghong Meng, Leonard Mestrandrea, Rainer Newman, Mickey Parish (FDA), Donald Singer, Scott Sutton, Edward Tidswell, Radhakrishna Tirumalai (USP)
2. http://www.usp.org/usp-nf/pharmacopeial-forum

Additional references

• USP 35-NF 30. 2012. United States Pharmacopeial Convention, Rockville, MD
• Tirumalai, R. 2012. “USP Improves, expands standards related to microbial contamination and bioburden control,” Amer. Pharm. Rev. May-June 2012, pp. 24-33
• Agalloco, J.P. and D. Singer. 2012. “Stay ahead of the curve–An update on sterility assurance topics in the USP,” J. Valid. Technol. 18 (3) pp. 24-28

Biography

Dr. Radhakrishna S. Tirumalai has been at USP since 2003 and is currently a Principal Scientific Liaison in the Global Science and Standards Division. He is the Staff Liaison to the USP Expert Committees on Microbiology and Toxicology. He works with industry, academia, regulatory agencies and other external science based organisations as the USP Expert Committee liaison in the development and revision of General Chapters in these areas. Dr. Tirumalai represents USP on PDA expert task forces and committees related to Microbiology and Sterility Assurance and on AAMI expert Working Groups related to Microbiology, Sterility Assurance and Biocompatibility.

Dr. Tirumalai’s prior industry experience encompasses process and product research and development, transfer, and product manufacturing. He has a PhD degree in Biochemistry. His postdoctoral work included studies on HIV and MuLV reverse transcriptases and bacteriophage lambda integrase. He has authored numerous publications and review articles. He is a frequent speaker at conferences and has taught Pharmacopeial Microbiology courses at numerous locations globally.