Pharmaceutical Container/Closure Integrity VI: A Report on the Utility of Liquid Tracer Methods for Evaluating the Microbial Barrier Properties of Pharmaceutical Packaging

Lee E. Kirsch

Abstract

The relationship between a liquid tracer package leak test (Mg ion ingress) and microbial immersion challenge test was demonstrated by direct and indirect correlation techniques. Rubber-stoppered glass vials with micropipette leaks were evaluated by a helium leak rate method, filled with broth, sterilized, and immersed in a bath containing microorganisms (E. coli /B. diminuta) and liquid tracer (Mg ions). After exposure and incubation, each unit was evaluated for liquid tracer ingress by atomic absorption spectrophotometry and for microbial ingress by visual inspection and blood agar streaking. Two hundred and eighty sterile broth-filled test units were challenged with microorganisms and liquid tracer. One hundred and fourteen units showed neither liquid tracer nor microbial ingress. One hundred and eight units were positive for both microbial and liquid tracer ingress. No test units were positive for microbial ingress but not for liquid tracer ingress. Fifty-eight units were positive for liquid tracer ingress but failed to show microbial ingress. Logistical regression was used to demonstrate that the probability of liquid tracer ingress was greater than microbial ingress at all leak sizes. The results indicate that the liquid tracer method studied herein was a useful indicator of the microbial barrier properties of pharmaceutical packaging. Additionally, the results support the contention that liquid penetration of a leak is required for microbial ingress.

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