In a prospective, single-blind, randomized study, a single 2-g dose of metronidazole was compared with a seven-day course of 500 mg given twice daily in the treatment of symptomatic vaginal discharge associated with Gardnerella vaginalis. Based on resolution of symptoms and on cultures negative for G vaginalis, 86% (40/46) of women treated with the single dose and 97% (35/36) of women treated with the seven-day course were considered cured at seven to ten days after treatment. Evaluation at 21 days after treatment, however, indicated that only 46% (16/34) of patients treated with the single 2-g dose were considered cured compared with 86% (26/30) of those treated with the seven-day course. Treatment of sexual contacts did not significantly improve cure rates in either group.
Swedberg J, Steiner JF, Deiss F, Steiner S, Driggers DA. Comparison of Single-Dose vs One-Week Course of Metronidazole for Symptomatic Bacterial Vaginosis. JAMA. 1985;254(8):1046-1049. doi:10.1001/jama.1985.03360080058029