Vaginal delivery of new formulations of nonoxynol-9 coprecipitated with polyvinylpyrrolidone in rabbits. Comparisons between two formulation delivery systems.

The objective of this study was to assess the efficacy of two formulation delivery systems (FDS) in preventing the onset of pregnancy in rabbits. Nonoxynol-9 (N-9) was coprecipitated with polyvinylpyrrolidone (PVP), which yields PVP/ N-9, and prepared as capsules or tablets. Semen specimens were collected (from eight male rabbits), pooled, and used for in vitro spermicidal assessment or artificial insemination (AI). In vitro spermicidal assessment was performed by introducing and mixing the FDS containing PVP or PVP/N-9 with 1.0 mL of semen, followed by incubation at 37 degrees C for 6 h. Semen samples were taken at various time intervals to determine killing of spermatozoa and dissolution of the FDS. The efficacy of the FDS in preventing the onset of pregnancy was assessed by inserting the FDS vaginally. The does were artificially inseminated at 0, 0.5, and 6 h after insertion of the FDS vaginally. The number of pregnant does and newborn rabbits was recorded. In the in vitro spermicidal trial, semen specimens exposed to both FDS containing PVP/N-9 were killed within 10 to 15 min of incubation. Tablets containing PVP only or PVP/N-9 dissolved completely after 3 h of incubation. However, capsules did not dissolve completely by 6 h of incubation. The results obtained in the in vivo trial showed that both FDS exhibited some variations in preventing the onset of pregnancy over the various time intervals following the insertion of tablets or capsules and AI. The tablet seemed to be a more efficient delivery system than the capsule, yielding significantly lower pregnancy rates at all three time intervals assessed. The tablet FDS, as applied in this study, was found to be the most efficient mode of delivery of the tested spermicidal formulations.