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January 1999


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Tony & Roz Cundell <[log in to unmask]>
Reply To:
The Pharmaceutical Microbiology Mail List <[log in to unmask]>
Mon, 25 Jan 1999 08:12:09 -0500
text/plain (53 lines)
At 08:01 PM 1/24/99 EST, you wrote:
>Help. I am faced with answering the question: What tests are available to
>determine if an organic drug substance, a tertiary amine hydrochloride drug
>substance, one that is a hemi-hydrate whose water of crystallization is
>approximately 3 % of the drug's molecular weight, will support or promote
>microbial growth?
>I am a chemist and not a microbiologist. I have always interpreted the
>Microbial Limit Tests in monograph <61>, USP 23, to answer this question with
>three possible conclusions: (1) the test specimen supports or promotes growth,
>(2) the test specimen is bacteriostatic, or (3) the test specimen is
>A colleague informs me that <61> does not  answer this question because the
>tests involve the use of materials or agents that themselves support growth.
>Monograph <61> does not or cannot determine that a drug substance by itself
>supports or promotes microbial growth. He proposes the water activity test to
>address this question. This test, used in the food industry, determines the
>level of active water associated with a test substance.There is a level of
>active water at or above which the test substance may be judged to support or
>promote microbial growth.
>I would appreciate if readers of this forum would comment on this question and
>the correct interpretation and significance of the Microbial Limit Tests <61>
>and the Water Activity test. Also, is there a difference in meaning with
>respect to the words support or promote with respect to microbial growth?
>Thank you.
>Stan Alekman


Bob Friedel published a paper in the the Pharmacopeial Forum on the use of
water activity determination in developing microbiological monitoring
programs for pharmaceutical and OTC drug products.

Bob is following up with a paper on raw materials.

Tony Cundell
Wyeth-Ayerst Pharmaceuticals
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