A phase I comparative postcoital testing study of three concentrations of C31G

C31G is a broad-spectrum antibacterial agent that shows contraceptive properties in vitro. This postcoital testing study evaluated the ability of three C31G concentrations, 0.5%, 1.0% and 1.7%, administered as a 3.5-mL dose of a vaginal gel to prevent sperm from entering mid-cycle cervical mucus. Irritation of the genitalia and acceptability were also assessed.

At baseline, a mid-cycle cervical mucus test and a postcoital test were performed within 24 h of each other without use of any study products to establish normal mid-cycle cervical mucus and sperm penetration. Subjects then completed up to three test cycles using one of the three concentrations of study product during intercourse.

Twenty-two of the 61 women enrolled completed a baseline cycle and at least one test cycle. An average of 14.6 progressively motile sperm per high power field was seen at baseline. This was reduced to 0.3 after use of 0.5% C31G, 0.5 after use of 1.0% C31G, and 0.4 after use of 1.7% C31G. There was no significant difference between test products (p >/= 1.000) but each test product was significantly different from baseline (p < 0.002). Very little genital irritation was observed. There were more reports of leakage and messiness with increasing C31G concentration.

This study suggests that all three concentrations of C31G are likely to give reasonable results in a contraceptive effectiveness trial. Based on the results of this and other trials, the 1.0% concentration has been selected for further development, including Phase III trials of contraceptive effectiveness.