A Cochrane review [Abstract] 1 included 14 studies with a total of 5 502 subjects. In the largest trial to date (n=1 536), the gel (Advantage® S) containing the lowest dose of nonoxynol-9 (52.5 mg) was significantly less effective in preventing pregnancy than were gels with higher doses of the same agent (100 mg and 150 mg). Probabilities of pregnancy by six months were 22% for the 52.5 mg gel, 16% for the 100 mg dose, and 14% for the 150 mg dose. In the same trial, the three different vehicles with 100 mg of nonoxynol-9 had similar efficacy. Interpretation of the results is limited, since 39% of participants discontinued the method or were lost from the trial. Few important differences in efficacy emerged in other trials.
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