Nitroimidazoles

crop_square Key points

  • check_circle Bactericidal synthetic antibiotics with an imidazole ring and attached nitro group
  • check_circle Damage bacterial DNA by producing free radicals
  • check_circle Excellent activity against anaerobes and some protozoa
  • check_circle Mostly well tolerated drugs

crop_square Background and biochemistry

Nitroimidazoles are a class of synthetic antibiotics with activity against anaerobic gram-positives, gram-negatives and protozoa. They have been in use since the 1960es. The most relevant and commonly used antibiotic of this class is metronidazole. As the name suggests, nitroimidazoles share a molecular structure consisting of an imidazole ring and a nitro group.

crop_square Mechanism of action

Nitroimidazoles easily penetrate cell walls. Inside the bacterial cell, a redox reaction takes place involving bacterial enzymes and the antibiotics' nitro group. This results in the creation of free radicals, which damage bacterial DNA eventually causing cell death. Nitroimidazoles are bactericidal. Resistance mechanisms are mediated by modification of bacterial enzymes involved in the redox reaction.

crop_square Drugs and spectrum of activity

  • Metro­nidazole
  • Tini­dazole

Nitroimidazoles have no activity against aerobe bacteria but provide excellent coverage of anaerobes. Metronidazole can be used in combination with other antibiotics to eradicate Helicobacter pylori. It is frequently used to treat Clostridium difficile infections.

crop_square Pharmacokinetics

Nitroimidazoles show high bioavailability after oral administration. Intravenous preparations are available. Tissue and blood-brain barrier penetration is excellent. They are metabolised in the liver and mostly excreted via the urine.

crop_square Adverse drug effects

Nitroimidazoles are generally well-tolerated drugs. Minor side effects include nausea, diarrhoea, stomatitis and alcohol intolerance.