Activated by the slow pace of progress in developing a vaccine for AIDS, one proposed approach to slow, or reduce the spread of HIV, is to prevent initial infection by the virus through the use of a microbicide. Microbicides are products that could be applied topically to the vagina to reduce transmission of HIV during intercourse. Topical delivery systems (TDS) are many and varied, ranging from ointments to creams/lotions and gels. Each type of TDS was originally designed, and formulated, for a particular application and, thereto, has its own specific advantages and limitations in terms of benefit performance. The first generation products used to test efficacy of anti-HIV microbicides for vaginal administration have been based exclusively on very simple gel formulations comprised of water-soluble polymers. Such formulations imply that the active material is, if not water-soluble, then at least water-dispersible, a fact that is often, demonstrably, not the case. From a practical perspective, these gels have been developed merely as a carrier for the active, with little emphasis on the effect of the formulation in practice, and the acceptability to potential users, i.e. real-life use.

All TDS, however, are multicomponent, heterogeneous compositions that require much iteration to attain the final desired formulation; many factors play a role in determining the outcome. The present paper will outline and review all the relevant factors affecting formulation of a TDS, especially as it applies to the development of a successful microbicide, laying out some basic principles and methods involved.