Sterility testing limitations

Currently the main application of interest for parametric release is to replace the sterility test as a control method in appropriate cases (given the limited value of that test to predict sterility assurance due to statistical considerations, although it is also pointed out that a sterility test provides a final opportunity to identify a major failure, although other means should provide a more reliable way of detecting such failures). The concept is applicable to well-founded methods of sterilization where the product stability is known and development data have identified the critical process parameters. The measured parameters should be such as to ensure that correct processing of the batch provides sufficient assurance that the sterility assurance level intended has been achieved. 

The USP 24 General Notices state that alternative methods may be used to determine that products comply with the pharmacopoeial standards for the advantages in accuracy, sensitivity, precision, selectivity, adaptability to automation or computerized data reduction, or any other special circumstances. Such alternative or automated methods shall be validated However, when disputed, the compendial method is conclusive as it is the official or referee test. In addition, USP Chapter (61) Microbial Limit Tests states that automated methods may be substituted provided they are validated and give equivalent or better results, whereas USP Chapter (71) Sterility Tests states that alternative procedures may be employed to demonstrate that an article is sterile, provided the results obtained are at least of equivalent reliability. 

USP 24 Testing Chapters (51) Antimicrobial Effectiveness Testing, (61) Microbial Limit Tests and (71) Sterility Tests, United States Pharmacopeial Convention, Inc., Rockville, MD, 2000. USP 24 Informational Chapters (1116) Microbiological Evaluation of Clean Rooms and other Controlled Environments, (1111) Microbiological Attributes of Pharmaceutical Articles, (1151) Pharmaceutical Dosage Forms, (1225) Validation of Compendial Methods, and (1231) Water for Pharmaceutical Purposes, United States Pharmacopeial Convention, Inc., Rockville, MD, 2000. 

This document contains information related to the liquid aseptic fill operation used in the manufacture of (product name), USP, at ABC Pharmaceutical Industries located at (provide postal address). Additional information to support the liquid aseptic filling validation includes but is not limited to environmental monitoring and controls, as well as product-specific testing such as bioburden and sterility testing. The main subsections are ... 

Unlike many dosage form specifications, the sterility specification is an absolute value. A product is either sterile or nonsterile. Historically, judgment of sterility has relied on an official compendial sterility test however, end-product sterility testing suffers from a myriad of limitations [1-4], The most obvious limitation is the nature of the sterility test. It is a destructive test thus, it depends on the statistical selection of a random sample of the whole lot. Uncertainty will always exist as to whether or not the sample unequivocally represents the whole. If it were known that one unit out of 1000 units was contaminated (i.e., contamination rate = 0.1%) and 20 units were randomly sampled out of those 1000 units, the probability of that one contaminated unit being included in those 20 samples is 0.02 [5], In other words, the chances are only 2% that the contaminated unit would be selected as part of the 20 representative samples of the whole 1000-unit lot. 

If microbial growth is detected in a sterility test, this may reflect a falsepositive reading because of the problem of accidental contamination of the culture media while performing the sterility test. The problem of accidental contamination is a serious yet unavoidable limitation of the sterility test. 

These major limitations demonstrate that reliance on end-product sterility testing alone in ascertaining the sterility of a parenteral product may lead to erroneous results. One purpose of validation in the manufacture of sterile products is to minimize this reliance on end-product testing. Three principles are involved in the validation process for sterile product. 

Testing Chapters Antimicrobial Effectiveness Testing, Ch. 51 Microbial Limit Tests, Ch. 61 Sterility Tests, Ch. 71. In U.S.P. 24. 

There are three significant limitations to the sterility test ... 

There have been major technological advances in two areas that mitigate some of the limitations of the sterility test. They are the use of isolation chambers for performing the test and the development of new technologies to provide rapid—approaching real time—sterility tests. 

The ATP bioluminescence method would detect any contaminated bacteria, if the bacteria were growing over its detection limit in the product. When many samples must be checked, it is possible to select whether each product is aseptic or not in a short time. Dubious samples would be tested by the ordinary plate method. The ATP bioluminescence method is one of the most available sterility tests for initiate screening. 

The manufacture of parenteral products is focussed at all times on the requirement for sterility of the finished product. Despite the fact that the regulators are clear in their preference for products to be terminally sterilized, the vast majority of parenterals are filtered through sterilizing grade filters and filled aseptically, primarily because stability considerations preclude the use of moist heat sterilization. The statistical limitations of sterility testing a sample... 

When applied to the finished product, a sterility test should be regarded as only the last in a series of control measures by which sterility is assured. Compliance with the test does not guarantee sterility of the whole batch since sampling may fail to select non-sterile containers and also the culture method used have limits to their sensitivity that will not necessarily permit growth of all microorganisms. 

Due to the rapid advancement of new pharmaceutical delivery systems, this chapter covers only a limited number of techniques. Several of the techniques listed below may be necessary only at time zero or at release rather than being monitored at each stability time point. In addition, this chapter does not cover microbiological tests such as microbial limit, pyrogen, and sterility testing. 

In addition, other tests specific to the drug substance and formulation may apply, such as sterility, microbial limits, bacterial endotoxin, and pH. These types of tests would also be called for in order to comply with local pharmacopoeial requirements. Tests for subvisible particles beyond what is required in the pharmacopoeia may also be necessary due to immunogenicity concerns [29]. 

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