Sensitivity of Trichomonas vaginalis to metronidazole, tinidazole, and nifuratel in vitro.

Prompted by the sensitivity of trichomonads to metronidazole and nifuratel in clinical practice, a study was conducted in 1971-1972 of 63 consecutive strains of Trichomonas vaginalis isolated from women with clinically refractory vaginal discharge. Their susceptibility to metronidazole, tinidazole, and nifuratel was tested, using a serial tube dilution technique. The minimum concentrations which in 48 hrs caused immobilization and lysis of trichomonads cultured in Diamond's medium was assessed. No differences in drug potency could be determined. The median trichomonistatic and trichomonicidal concentrations were 0-1 and 0-6 mug/ml. respectively when using an inoculum of 10,000 organisms per ml. An inoculum of 100,000 per ml. resulted in inhibitory concentrations of 1-0 and killing concentrations of 3-3 mug./ml. These levels are readily attained in blood and vaginal tissue after oral ingestion of the two imidazole derivatives. Thus, metronidazole has maintained its efficacy since it was first introduced more than a decade ago. The few therapeutic failures with metronidazole and tinidazole are considered to have been caused by pharmacokinetic deficiencies in the patients, or by re-infection.