Metronidazole (Flagyl)

Prophylaxis timing - Give within 60 minutes before incision (start the infusion earlier as it runs over 30-60 min); redose about every 6-8 hours for long cases. Combined with a cephalosporin for colorectal coverage.

Alcohol/propylene glycol - Classic disulfiram-like reaction with ethanol; also avoid IV formulations containing propylene glycol concerns with large doses.

QT and neurotoxicity - Rare QT prolongation; prolonged or high-dose therapy risks neuropathy, relevant for repeat perioperative dosing.

Drug Interactions - Potentiates warfarin (raises INR); inhibits alcohol metabolism (disulfiram-like reaction); levels raised by cimetidine, lowered by enzyme inducers; may raise lithium levels.

Pediatric Implications - Weight-based (15 mg/kg); well established in children for anaerobic and protozoal infections.

Obstetric Implications - Category B; crosses the placenta. Generally considered acceptable after the first trimester; present in breast milk, so some advise a brief interruption of nursing after large single doses.

Relative:

First trimester of pregnancy (relative)

Active CNS disease

Severe hepatic impairment (dose-adjust)

Caution:

Concurrent alcohol or alcohol-containing preparations

Anticoagulation with warfarin

Surgical prophylaxis: 500 mg IV (about 7.5 mg/kg, max 4 g/day) infused over 30-60 min within 60 min of incision (adult); 15 mg/kg (pediatric).

Reduced within anaerobic organisms to reactive nitroso intermediates that disrupt bacterial/protozoal DNA, causing strand breakage and cell death.

Hepatic

Renal

Infuse over 30-60 min (not IV push). Avoid alcohol during and for 3 days after therapy.