Pharmacokinetics of nitroimidazoles. Spectrum of adverse reactions

A short review is given of the pharmacokinetic characteristics and side effects of the nitroimidazoles: metronidazole, tinidazole and ornidazole. The drugs are well absorbed from the gastrointestinal tract, maximum plasma levels generally being obtained 1 to 4 h after oral intake. Metronidazole has been shown to be absorbed after rectal administration; vaginal absorption is documented for all three drugs. The nitroimidazoles are widely distributed in the body, cross the placenta and appear in breast milk. Therapeutically effective concentrations of e.g. metronidazole have been demonstrated in e.g. the central nervous system, middle ear discharges, bile, peritoneal fluid, and fluids and tissues of the female genital tract. The binding to plasma proteins is less than 20%. Available data suggest that the elimination half-lives of these drugs differ, being 7-8 h for metronidazole, about 12 h for tinidazole and 14-15 h for ornidazole. Both metronidazole and ornidazole, but not tinidazole, seem to be extensively metabolized before elimination. The nature and frequency of adverse reactions to this drug include encephalopathy in a few patients treated with doses between 5 and 10 g daily as an adjunct to radiotherapy, and peripheral neuropathy observed in patients treated for prolonged periods with high doses. Among the common side effects of the nitroimidazoles are symptoms from the gastrointestinal tract such as nausea, anorexia, vomiting and metallic or bitter taste. Dizziness, ataxia and headache have been reported. When given together with alcohol, a disulfiram-like intolerance reaction can be obtained.