Metronidazole radical anion generation in vivo in Trichomonas vaginalis: oxygen quenching is enhanced in a drug-resistant strain.

The nitro radical-anion of metronidazole has been detected in vivo in the sexually transmitted human parasite, Trichomonas vaginalis, under anaerobic conditions by electron spin resonance spectrometry. Exposure of organisms to oxygen decreased the intensity of the radical signal in both metronidazole-sensitive ATCC strain 30001 and in the metronidazole-resistant strain 85. The sensitive strain still gave radical signals at partial pressures of oxygen (greater than 6 kPa) sufficient to remove all detectable radicals from the resistant strain. This evidence suggests that the resistant strain has defective oxygen scavenging system(s).