CEI-MS-06 — worked example

§6Worked example

§6.1Worked example — sample numbers and the limits of the inference

1. A batch of 400 vials of a lyophilised peptide is to be tested. The pharmacopoeial table specifies, for a batch of more than 200 containers, testing of 2 % of the batch or 20 containers, whichever is the lesser: 2 % of 400 is 8, so 8 containers are tested.
2. Suppose the batch has a true contamination rate of 1 %, that is 4 contaminated vials in 400. The probability that a given tested vial is uncontaminated is 0.99, so the probability that all 8 tested vials are uncontaminated is 0.99⁸ = 0.923.
3. The test therefore has a 92 % chance of passing a batch that contains four contaminated vials.
4. This is not a criticism of the pharmacopoeial method, which is designed to be used alongside process validation and aseptic-process simulation rather than as a standalone release criterion. It is, however, the reason the Institute states that a sterility result on a research-supply batch — where no process validation exists to accompany it — provides much weaker assurance than the words "sterility test: complies" suggest.

§6.2Illustrative mass balance

References cited on this page

References are numbered in order of first citation in this document. Each superscript in the text links to its entry below.

1. United States Pharmacopeial Convention. General Chapter ⟨71⟩ Sterility Tests. United States Pharmacopeia — National Formulary (USP–NF) 2024;USP 2024 Issue 1. identifier not held by the Institute
2. United States Pharmacopeial Convention. General Chapter ⟨85⟩ Bacterial Endotoxins Test. United States Pharmacopeia — National Formulary (USP–NF) 2024;USP 2024 Issue 1. identifier not held by the Institute

Identifiers are reproduced only where the Institute holds them. Where a digital object identifier or PubMed identifier is not shown, the Institute has recorded the journal and year and has not constructed an identifier.