Finished products where antimicrobial agents are added to preparations such as multiple dose injections,
topical creams, and oral liquids, an assay with limits should be included in the specifications.
An antimicrobial preservative effectiveness testing is performed during the development phase of the product
to establish the minimal effective level of preservatives that will be available up to the stated expiry date, and
for which a single regular production batch of the drug is to be tested for antimicrobial preservative
effectiveness at the end of the proposed shelf life. Once the minimal effective preservative level has been
determined, all lots of any preservative containing dosage form included in the stability program must be
tested at least once at the expiry date for preservative content. For sterile drugs, the declaration of
preservatives on the label is mandatory and those should be treated as for active ingredients (i.e., tested for
preservative content at pre-established control points for those batches enrolled in of the continuing stability
program). Where the lower limit of the preservative is less than 90 percent of label claim, the challenge test
should be performed on samples at or below the lower limit. The challenge test need not be included in the
specifications, provided that an assay for the preservative is included.
