Metronidazole: Nitroimidazole Antibiotic Guide for Anaerobic and Protozoal Infections

Metronidazole treats anaerobic and protozoal infections. Learn the mechanism, spectrum, indications, side effects, and drug interactions.

Introduction

Nitroimidazoles are bactericidal and antiprotozoal agents that target anaerobic bacteria and protozoa. Metronidazole is the main medication used for infections. It’s often chosen for gastrointestinal, gynecologic, and intra-abdominal issues.

Medications in the Class

• Metronidazole (prototype)

• Tinidazole

• Ornidazole

Mechanism of Action

Anaerobic cells reduce metronidazole. It forms reactive metabolites that bind to DNA. This binding causes strand breakage and stops nucleic acid synthesis. This results in bacterial and protozoal cell death.

Spectrum of Activity

• Anaerobic bacteria: Bacteroides fragilis, Clostridium spp., Fusobacterium.

• Protozoa: Trichomonas vaginalis, Giardia lamblia, Entamoeba histolytica

• Gram-positive and Gram-negative aerobes are generally resistant.

Indications (When Used)

• Bacterial vaginosis and trichomoniasis

• Clostridioides difficile infection (alternative)

• Intra-abdominal infections in combination therapy

• Giardiasis and amoebiasis

• Prophylaxis in colorectal surgery

Contraindications (When Not to Use)

• Hypersensitivity to metronidazole or other nitroimidazoles.

• First trimester of pregnancy (use only if necessary)

• Severe hepatic impairment

Side Effects

• Gastrointestinal upset: nausea, vomiting, and metallic taste.

• CNS: headache, dizziness, peripheral neuropathy (long-term use)

• Disulfiram-like reaction with alcohol.

• Rare: seizures, neutropenia, hepatotoxicity

Drug Interactions

• Alcohol causes a disulfiram-like reaction.

• Warfarin: increased anticoagulant effect.

• CYP3A4 substrates: minor interactions, but caution with phenytoin and lithium.

Antidote

No specific antidote; supportive care and discontinuation if toxicity occurs.

Monitoring of Potential Complications

• Neurologic symptoms during prolonged therapy.

• Liver function tests for long-term therapy.

• CBC if prolonged or repeated courses.

• Monitor for superinfection (e.g., oral or vaginal candidiasis).

Nitroimidazoles like Metronidazole are essential for anaerobic bacterial and protozoal infections. They work well, but be careful with alcohol. Also, watch for any nerve or liver issues.