Chapter 34 : 5-Nitroimidazoles

Abstract:

This chapter summarizes information related mainly to the antibacterial activity of the 5-nitroimidazoles. Three 5-nitroimidazoles have been selected: metronidazole, ornidazole, and tinidazole. Metronidazole is the prototype and is therefore used most often as the representative molecule of the class; tinidazole is principally used as an antiprotozoal agent. The 5-nitroimidazoles are very active against the majority of gram-negative anaerobic bacteria and Clostridium. Anaerobic gram-positive cocci are more often susceptible to 5-nitroimidazoles, even if in the majority of studies 2 to 10% resistant strains are observed. Ornidazole levels measured in the cerebrospinal fluid (CSF) and brain represent at least 80% of levels in plasma; the same applies to concentrations in appendiceal fluid. The apparent elimination half-life and plasma clearance of ornidazole in nondialyzed subjects with renal insufficiency are similar to those in subjects with normal renal function. In patients with hepatic insufficiency, the peak concentrations in plasma occur later and the apparent elimination half-lives are prolonged. It is on the neurologic level that the most serious adverse effects are observed during high-dose and/or prolonged treatments. The three 5-nitroimidazole derivatives have very similar antibacterial properties; the pharmacokinetics are very similar, with a longer apparent elimination half-life for ornidazole than for metronidazole, possibly allowing the number of doses of ornidazole to be reduced. These 5-nitroimidazoles derivatives have excellent in vitro activity and well-established clinical efficacy in the treatment of anaerobic infections or in mixed infections when combined with antibiotics effective against aerobes.