Metronidazole-resistant Trichomonas vaginalis.

A 36-year-old woman with symptomatic metronidazole-resistant trichomonal vaginitis for 10 years had a total of 22 courses of treatment with either metronidazole or tinidazole according to different schedules. The minimum trichomonicidal concentration of metronidazole for the strain of Trichomonas vaginalis isolated from the patient was 160 microgram/ml compared with 1.25-10 microgram/ml for other freshly isolated strains. The former strain also showed a definitely decreased sensitivity to ornidazole and tinidazole (80 microgram/ml). The mechanisms behind the appearance of resistance in this clinical isolate are at present unknown and require further study from the theoretical as well as the therapeutic viewpoint.