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