A laboratory method to evaluate formulation effects on the in vitro antimicrobial activity of topical creams and ointments.

A simple and reproducible method is described to assess the effect of formulation on the bactericidal and fungicidal activity of topical antimicrobial agents. The technique involves direct inoculation of test and control articles followed by aliquot sampling, neutralization of active antimicrobial ingredients and enumeration of viable microorganisms by standard methods. Two silver sulphadiazine cream formulations, differing in their aliphatic alcohol content, were evaluated as manufactured and in diluted forms in this manner using three bacterial and one fungal burn wound isolates. Results were analysed by a multivariate analysis of variance to test formulation effects, concentration effects and their interaction over time. The results demonstrate that the antimicrobial activity of both creams is equivalent.