Objective: To compare the safety and effectiveness of 5% and 1% imiquimod cream with vehicle cream in the treatment of external anogenital warts.

Design: Randomized, double-blind, placebo-controlled comparison that evaluated patients for total clearance of their warts. Patients who experienced total clearance were evaluated for recurrence in a 12-week follow-up.

Setting: Eleven ambulatory offices, including both private physician offices and referral medical centers.

Patients: Three hundred eleven healthy men and women aged 18 years or older with 2 to 50 external anogenital warts were recruited from the practices of investigators, referring physicians, and advertisements. Eighty-two additional patients were screened but did not qualify. Four patients discontinued use of the medication because of adverse effects.

Interventions: Five percent imiquimod (Aldara) cream, 1% imiquimod cream, or vehicle cream was applied to all external warts overnight 3 times each week for 16 weeks, or until all treated warts disappeared, whichever occurred first.

Main outcome measurements: The number of patients experiencing the elimination of all baseline warts and the recurrence rate of these warts. In addition, the reduction in baseline wart area the duration of therapy required to eliminate warts, and the frequency and severity of adverse reactions were principal measurements.

Results: In the intent-to-treat analysis, 54 (50%) of 109 patients who received 5% imiquimod cream, 21 (21%) of 102 of those who received 1% imiquimod cream, and 11 (11%) of 100 patients treated with vehicle cream experienced eradication of all treated baseline warts. The difference between the effectiveness of 5% imiquimod cream and the vehicle cream was statistically significant (P < .001). Of those patients whose warts cleared during therapy, 13% of patients who received 5% imiquimod experienced a recurrence of at least 1 wart. Recurrences occurred in none of the patients who used 1% imiquimod cream and in 10% of patients who used the vehicle cream. Local erythema was the most common adverse reaction, but the majority of patients in each group experienced no or only mild local inflammatory reactions. There were no differences in incidences of flulike symptoms among treatment groups.

Conclusions: Five percent imiquimod cream is an effective and safe self-administered therapy for external anogenital warts when applied 3 times a week overnight for up to 16 weeks. The recurrence rate is low.