Bioburden in the Focus of Pharmaceutical Quality

Bioburden refers to the microbial load of a product or material prior to sterilization. In pharmaceutical quality control, bioburden determination is used to quantify the number and type of microorganisms on raw materials, intermediate products, and end products. This is essential for validating the effectiveness of sterilization and minimizing contamination risks.

As part of quality assurance, bioburden monitoring ensures that manufacturing processes are carried out under controlled hygienic conditions. It supports compliance with regulatory requirements such as GMP (Good Manufacturing Practice) and helps to identify deviations at an early stage. Consistent bioburden control is therefore an important part of ensuring product quality and patient safety.

Development

The issue was therefore taken up by regulators years ago. In Pharmacopeial Forum 39(4), the United States Pharmacopeia (USP) published the draft chapter <1115> entitled “Bioburden Control of Nonsterile Drug Substances and Products” in 2014. This document presented a risk-based approach to controlling potential microbial contamination during the manufacture of non-sterile drugs. However, the issue of bioburden contamination is by no means limited to non-sterile products. The current Annex 1 of the European GMP guidelines explicitly emphasizes that suitable pre-filters can be used to reduce microbial contamination and that sterilization filters can be used at various points in the manufacturing process. In addition, the guidelines require bioburden monitoring prior to sterilization. For this step, workplace-specific limit values must be defined that relate to the efficiency of the sterilization process used. The guideline also stipulates that the bioburden test must be performed for each batch, regardless of whether the products are aseptically filled or terminally sterilized. There are also international guidelines: bioburden testing for medical devices is regulated worldwide by ISO 11737.

These current developments have prompted us to revisit the topic of bioburden control in discussions with experts, e.g., from the ECA's Pharmaceutical Microbiology Working Group, and to discuss different perspectives on this important quality criterion. Discussions with experts from the fields of pharmacopoeia, pharmaceutical quality control, and testing laboratories highlight the challenges associated with establishing a bioburden control strategy and the issues that can be expected during implementation.

Questions

A key topic was the development of bioburden control strategies geared toward the various phases of the product life cycle. These include the early clinical phase, the late clinical phase, and the commercial phase. Another question that arose was whether testing should focus on “specified microorganisms” or “undesirable microorganisms.” This applies to all relevant stages, from testing raw materials to in-process controls, the drug substance, the drug product, and the final product.

Another topic of discussion was biofilms, their biology, and methods for identifying biofilms in bioburden development.
A further important topic is the question at which points in the process bioburden tests should be carried out. This includes the pre-definition of bioburden or endotoxin levels in raw materials and the assessment of whether “undesirable microorganisms” are present in the raw materials used. Various test methods are used, including the Total Aerobic Microbial Count (TAMC), the Total Yeast and Mold Count (TYMC), the Most Probable Number (MPN) method, other classic bioburden test methods, and modern rapid microbiological methods.

The question of whether bioburden samples should have a limited shelf life was also discussed, as was the handling of so-called “missing bioburden” results. With regard to limit values, the question also arose as to whether it makes sense to set predefined bioburden and/or endotoxin limit values for upstream or downstream processes - including fermentation - as well as for the overall process.

Another point of discussion revolved around the question of which control system is preferred: a two-stage system with warning and alarm limits or a three-stage system that additionally includes a rejection limit. The method used to set the limit values also plays a role here, for example, how many data points are required for this and what philosophy is applied to new processes without empirical values.

Deviation management was another focus: Is identification of the germs always carried out in the event of limit violations? If so, in which cases - for every colony or only for violations? The question of preferred identification techniques and appropriate measures in the event of limit violations also arises.

Current support for questions relating to bioburden

In order to devote more attention to this topic, the ECA Microbiology Working Group has compiled and recently published a Q&A paper on bioburden, which answers a large number of questions posed to the experts. You will find the Q&A document in the members' area of the Pharmaceutical Microbiology Group's website. To apply for membership, just complete the registration form - membership is free of charge.