ABSTRACT
The antimicrobial activity displayed by preservatives in simple aqueous solutions may be substantially modified by excipients in the formulation. Because micro-organisms require water to metabolise and grow, anhydrous pharmaceuticals are normally vulnerable to microbial spoilage; thus, they usually do not include an antimicrobial preservative. To persons with limited microbiological experience, it may be tempting to assume that it should be possible to rely on chemical assays to provide the necessary assurance of preservative protection. The preservative efficacy tests described in the US Pharmacopeia and European Pharmacopoeia are similar in principle and in several features of the detailed methodology. The organisms employed realistically represent common contaminating species or those that pose a problem in terms of infection potential or resistance to preservatives. On initial inspection, the preservative testing procedures described in the major pharmacopoeias might appear to be sufficiently informative to achieve reproducible results when the test is applied to the same batch of product by different testing laboratories.
