Postcoital, Vaginal, spermicidal potency of formulations: the Macaca arctoides (stumptailed macaque) as animal model

The Macaca arctoides (stumptailed macaque) was found to be a good animal model for determining the postcoital spermicidal activity of vaginal preparations. The stumptailed macaque is easy to handle, so formulations can be inserted correctly into the vagina just before coitus. The male mates rapidly, and the entire test can be completed within 5 to 10 minutes, minimizing all extraneous factors other than those inherent to the reproductive tract and the coital act. Data from postcoital breeding experiments were found to be reliable and consistent when results of six primate mating tests for a single dose level of a test formulation were averaged. Dose-response curves can be prepared from these average results, and the relative in vivo effectiveness of the spermicides can be determined. The Sander-Cramer test proved to be a good assay with which to quantitate the in vitro spermicidal potency of formulations. The spermicidal preparations tested immobilized human and primate spermatozoa in vitro to the same extent with the exception of one formulation (possibly due to the vehicle in which the active ingredient was incorporated). The relative spermicidal effectiveness of preparations differs with in vitro and postcoital testing. Because the latter is a more realistic indicator of the contraceptive potency of a formulation, it is recommended that postcoital primate experiments be performed with newly developed vaginal spermicides before extensive animal breeding experiments clinical trials are initiated.