ABSTRACT
Preservation of pharmaceuticals, cosmetics and toiletries is necessary to prevent formulations from becoming infected with highly resistant and hazardous micro-organisms during their repeated use. Preservative efficacy tests are described in the British Pharmacopoeia (BP), the United States Pharmacopoeia (USP) and European Pharmacopoeia. The USP has specific requirements for sterile aqueous injectable, ophthalmic, otic and nasal products which are not applicable to aqueous topical and oral products. Preservative efficacy therefore has to be based solely on the performance of the preserved formulation rather than on a comparative evaluation of an unpreserved and preserved formulation, which provides a more discerning method of assessment. Procedures using mixed-culture challenges are described by the Society for Cosmetic Chemists for shampoos, creams, lotions and eye cosmetics. With shampoos, bacteria are selected to include Pseudomonas species isolated from spoilt shampoo or detergent preparations. Preservative efficacy, with assessment based on the BP 1988 challenge test, should be ensured over the shelf-life by rechallenging stored product at intervals.
