USP General Chapter 71 (revision 20)

USP General Chapter 71, titled Sterility Tests, prescribes the media, incubation conditions, sample quantities and method-suitability procedures for demonstrating that a sample yields no microbial growth. It is a mandatory chapter where a monograph or regulatory requirement invokes it.^[1]

The chapter is explicit that a passing result is not proof of sterility of a batch. Sterility assurance derives from process design and validation; the compendial test is a final check with limited statistical power, and the chapter's companion informational chapter on sterility assurance says so at length.^[2]

Like the endotoxin chapter, it is harmonised in substance with the corresponding European and Japanese pharmacopoeial chapters.^[1]

The chapter names two media — fluid thioglycollate medium, incubated at 30–35 °C, and soybean–casein digest medium at 20–25 °C — and requires incubation for not less than fourteen days. It specifies growth-promotion testing of each medium lot against named challenge organisms before use.^[1]

Sample quantities are tabulated by container size and batch size. The number of containers tested is small in absolute terms, which is the source of the statistical limitation discussed at Sterility testing.

Method suitability, formerly called the bacteriostasis and fungistasis test, requires demonstrating that the sample does not inhibit growth of the challenge organisms under the conditions used. Where the sample is inhibitory, the method must be modified — by filtration and washing, by neutralisation, or by dilution — until recovery is demonstrated.^[1]

Membrane filtration is preferred where applicable because it separates the sample from the growth medium: the organisms are retained on a 0.45 μm membrane, the sample and any inhibitory component pass through, and the washed membrane is incubated.^[1]

The pore size is a compendial convention rather than an absolute cut-off. Organisms smaller than the nominal rating exist, and filtration is a retention process rather than a sieve, so retention is probabilistic. This is one of several reasons the chapter is framed as a test rather than as proof.

For a lyophilised powder, filtration requires dissolution in a suitable diluent, which introduces a step at which contamination can be added or an inhibitory solvent can interfere. The suitability demonstration covers this, which is why it is not optional.^[2]

Research-chemical peptides are not manufactured or released as sterile products, and the chapter does not apply to them. Certificates for such material do not ordinarily carry a sterility determination.^[3]

Where a sterility claim appears, the same distinction applies as for the endotoxin chapter: "tested by the method of USP <71>" is a claim about method provenance, while conformity to a sterility requirement is a claim about regulatory status that a research chemical does not have.

The practical position is that such material should be regarded as non-sterile. Related handling considerations are treated at Reconstitution of lyophilised peptides, Bacteriostatic water and Beyond-use date, and the compounding chapter sets out the practice expected where sterile preparations are genuinely made.^[4] Nothing here is medical advice and research-use compounds are not approved for human administration.^[3]

• Sterility testing
• USP General Chapter 85
• Bacterial endotoxin test
• Beyond-use date
• Bacteriostatic water