Vaginal PO2 in healthy women and in women infected with Trichomonas vaginalis: potential implications for metronidazole therapy.

We measured the PO2, pH, and temperature in the vaginal canals of nine patients with symptomatic Trichomonas vaginitis and those of 10 healthy women. The patients included eight women with primary infections caused by metronidazole-susceptible strains and one refractory case that resulted from infection with a metronidazole-resistant Trichomonas vaginalis. The median vaginal PO2, pH, and temperature in the patient group were 1 mm Hg, 6, and 37.3 degrees C respectively; these medians were 1 mm Hg, less than or equal to 4.5, and 37.2 degrees C in the healthy group. These data show that vaginal environment is anaerobic or microaerophilic (it has reduced oxygen tension). Because the activity of metronidazole is reduced under aerobiosis, the vaginal environment should enhance the biologic activity of the drug.