Development pharmaceutics of microbicide formulations. Part I: preformulation considerations and challenges.

Microbicides, the compounds and formulations that can prevent transmission of sexually transmitted diseases (STDs)/HIV are being pursued actively as a promising AIDS intervention. The drug development chain for a topical microbicide differs significantly from that of any systemic or topical compound/formulation regarding to time line, cost, activities, and milestones. This is in part because of the lack of standard in vitro models to assess efficacy, and complex ethical issues in clinical trials of microbicides. Several factors, including changes in the physiology of the cervix and vagina with age and menstrual cycle, intercourse, as well as leakage of the formulation from the vagina may affect their design, development, and performance. Selection and development of optimal microbicide delivery systems (gel/cream, pessary, film, tablet, foam, etc.), their inactive ingredients, manufacturing details, and packaging system are dependent on the properties of active drug, or their preformulation parameters (PP). The PP of the active drug substance needs to be evaluated in initial stages of drug discovery and development so that the most suitable delivery system can be selected. Some PP of microbicide agents include physical state, organoleptic properties (color, odor, appearance, taste, etc.), molecular weight, aqueous solubility, hygroscopicity, acidity/alkalinity, permeability and absorption characteristics, stability in solid/solution state, and inherent bioadhesiveness. Thus, a well-coordinated, planned, and implemented preformulation program can help in not only accelerating microbicide formulation development, but also to minimize unforeseen failures in subsequent stages of the development. The objective of this review is to highlight the significance of PP, suggesting a systematic preformulation program.