Susceptibility of Trichomonas vaginalis strains to metronidazole: response to treatment.

The effect of the susceptibility of Trichomonas vaginalis strains to metronidazole on response to treatment was determined from minimal inhibitory concentrations (MICs) for organisms isolated during a clinical trial in which single 1- and 2-g doses of metronidazole were compared. Fifty-seven strains were isolated from patients receiving 1 g of metronidazole, and 75 from those receiving 2 g. The mean MIC for all strains was 1.50 microgram/ml (range, 0.5-4.5 microgram/ml) and was similar in both groups. The mean MICs for isolates from patients who were cured were significantly less than the mean MICs of isolates from those who were treatment failures. The cure rates, compared to the MICs for the strains isolated, varied from 84% (MIC, 0.5 microgram/ml) to 16% (MIC, greater than or equal to 3.0 microgram/ml) for the group given the single 1-g dose and from 94% (MIC, 0.5 microgram/ml) to 43% (MIC, greater than or equal to 3.0 micrograms/ml) for those given the 2-g dose. The data demonstrate a direct relationship between susceptibility of T. vaginalis isolates and response to treatment with single-dose regimens of metronidazole.