Ph. Eur. 2.6.1. Sterility

Ph. Eur. 2.6.1 defines the compendial sterility test applied when a European Pharmacopoeia monograph requires an article to be sterile.

The chapter describes culture-based detection of viable microorganisms using defined media and incubation conditions, and is harmonized with USP <71> and JP 4.06 under ICH Q4B Annex 8(R1).

In practice, sterility testing provides confirmatory evidence within a broader sterility-assurance strategy driven by validated manufacturing, aseptic processing, and GMP controls, rather than proof of sterility by testing alone.

Method A – Membrane Filtration (preferred when feasible):
• Filterable products
• Products containing preservatives

Method B – Direct Inoculation (when filtration is not feasible):
• Oils and ointments
• Highly viscous products

Always confirm regional pharmacopoeial implementation details and PDG notes.

The test is part of a broader sterility-assurance strategy primarily driven by validated manufacturing processes, aseptic processing controls, and GMP systems. 

Core principle. Culture-based detection using two media—Fluid Thioglycollate Medium (30–35 °C) and Soybean-Casein Digest Medium (20–25 °C)—with not less than 14 days incubation. Media must be qualified by growth promotion testing using low inocula of defined challenge organisms, as specified in the harmonized texts.

Method suitability includes demonstration that the product does not inhibit recovery of inoculated microorganisms (bacteriostasis/fungistasis).

Sampling Plan (Minimum Number of Items Tested)

Ph. Eur. 2.6.1 (and the harmonized USP <71>) specify a minimum number of units to be tested per batch, based on batch size and presentation, as part of the sterility test.

Because sterility testing has limited statistical power, the compendial sampling plan provides baseline assurance that must be supported by validated manufacturing controls and process validation. CMC reviewers expect the sterility section to clearly state the number of units tested per batch and to confirm alignment with the applicable pharmacopoeial table, or to provide justification where deviations are proposed.

The exact sampling requirements and any qualifiers should always be confirmed in the official pharmacopoeial text and regional implementation guidance.

Test methods (harmonized options).

• Method A: Membrane filtration (preferred when feasible).

• Method B: Direct inoculation (for non-filterable products).
  Testing must be performed aseptically, preferably in an isolator. Grade A cleanroom environments are acceptable when appropriately justified.

Harmonization: Under ICH Q4B Annex 8(R1), Ph. Eur. 2.6.1, JP 4.06, and USP <71> are interchangeable in ICH regions, subject to the Annex’s qualifications (e.g., notes on rinsing/diluting fluids and execution details). Always confirm regional implementation and PDG sign-off notes.