METRONIDAZOLE IN PLASTIC CONTAINER
Clinical safety rating: safe
Disulfiram-like reaction can occur with alcohol Can cause peripheral neuropathy and seizures with prolonged use.
After intracellular reduction, metronidazole and its metabolites interact with DNA leading to inhibition of nucleic acid synthesis and cell death. It is active against anaerobic bacteria and protozoa.
| Metabolism | Hepatic metabolism primarily via oxidation, conjugation; main metabolite: hydroxy metabolite (active). Enzymes: CYP450 (minor). |
| Excretion | Renal (60-80% as unchanged drug and metabolites), fecal (6-15%), biliary (<5%) |
| Half-life | 8 hours (range 6-12 hours) in adults with normal hepatic function; prolonged to 15-30 hours in severe liver disease |
| Protein binding | Less than 20%, primarily to albumin |
| Volume of Distribution | 0.6-0.8 L/kg, indicating extensive tissue penetration |
| Bioavailability | Oral: approximately 80% (range 60-100%); IV: 100% |
| Onset of Action | IV: immediate; oral: 1-2 hours; topical: 2-6 hours |
| Duration of Action | 12-24 hours; dosing typically every 6-8 hours for systemic infections |
| Molecular Weight | 171.15 |
500 mg IV every 8 hours or 7.5 mg/kg IV every 6 hours (loading dose 15 mg/kg) for most anaerobic infections.
| Dosage form | INJECTABLE |
| Renal impairment | GFR > 50 mL/min: No adjustment; GFR 10-50 mL/min: 500 mg IV every 12 hours; GFR < 10 mL/min: 500 mg IV every 24 hours or 250 mg IV every 12 hours; Hemodialysis: Administer 500 mg IV post-dialysis; Peritoneal dialysis: Usual dose or 250 mg IV every 12 hours. |
| Liver impairment | Child-Pugh A: No adjustment; Child-Pugh B: Reduce dose by 50% every 8 hours or administer 500 mg IV every 12-16 hours; Child-Pugh C: Avoid use or use with extreme caution, monitor levels. |
| Pediatric use | Neonates (<7 days): 7.5 mg/kg IV every 12-24 hours based on gestational age; Infants 7-28 days: 7.5 mg/kg IV every 8-12 hours; Children (≥1 month): 30 mg/kg/day IV divided every 6 hours, maximum 4 g/day. |
| Geriatric use | No specific dose adjustment required, but monitor renal function; reduce dose based on creatinine clearance as per renal adjustment; consider increased risk of adverse effects. |
| 1st trimester | Use is generally avoided due to possible teratogenic risk; however, available data do not show a consistent increase in major malformations. Some studies suggest an association with cleft lip/palate, but absolute risk is low. Use only if clearly needed. |
| 2nd trimester | Use with caution. Metronidazole crosses the placenta and is considered safe for short-term use in pregnancy, particularly for treatment of trichomoniasis or bacterial vaginosis. No evidence of fetal harm from multiple cohort studies. |
| 3rd trimester | Use with caution near term; theoretical risk of neonatal hepatic toxicity due to immature metabolism, but clinical significance is unclear. Avoid high-dose or prolonged use. |
Clinical note
Disulfiram-like reaction can occur with alcohol Can cause peripheral neuropathy and seizures with prolonged use.
| FDA category | Human |
| Placental transfer | Metronidazole readily crosses the placenta, achieving fetal serum concentrations similar to maternal levels. The degree of transfer is high (fetal/maternal ratio ~1.0). |
■ FDA Black Box Warning
Carcinogenicity: Metronidazole has been shown to be carcinogenic in mice and rats. Relevance to humans is unknown. Avoid unnecessary use.
| Common Effects | protozoal infections |
| Serious Effects |
Hypersensitivity to metronidazole or other nitroimidazole derivatives
| Precautions | Carcinogenicity risk (avoid chronic use), Seizures and peripheral neuropathy (discontinue if abnormal neurologic signs occur), Hepatic impairment: use with caution, monitor for toxicity, Renal impairment: no dose adjustment usually needed, but monitor for accumulation, Drug interactions with warfarin (increased INR), disulfiram-like reaction with alcohol, Pregnancy category B: use only if clearly needed, Lactation: caution, metronidazole excreted in breast milk |
| Food/Dietary |
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| Breastfeeding | Metronidazole is excreted into breast milk with peak concentrations after maternal IV administration. A relative infant dose of 5-15% of the maternal weight-adjusted dose is estimated. Short-term use is likely compatible with breastfeeding, but avoid high-dose or prolonged therapy. The American Academy of Pediatrics considers it usually compatible, but some experts recommend discarding milk for 12-24 hours after a single high-dose (2 g) to reduce infant exposure. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Metronidazole crosses the placenta. First trimester: limited data; avoid unless essential. Second/third trimesters: no increased risk of major malformations reported; use if clearly needed. |
| Fetal Monitoring | Maternal: CBC, liver function tests if prolonged use. Fetal: no specific monitoring; standard prenatal care. |
| Fertility Effects | No evidence of impaired fertility in humans; animal studies show no effect. |
| Avoid alcohol and any foods or medications containing alcohol or propylene glycol. No other specific food restrictions, but may take with food to reduce GI upset. |
| Clinical Pearls | Metronidazole IV in plastic container is a nitroimidazole antibiotic with bactericidal activity against anaerobes and protozoa. It penetrates well into CNS and abscesses. Avoid alcohol during and for 48 hours after therapy due to disulfiram-like reaction. Monitor for peripheral neuropathy with prolonged use. Dose adjustment required in severe hepatic impairment (Child-Pugh C). May prolong INR in warfarin patients. Use with caution in patients with history of seizures. Discontinue if neurologic symptoms develop. |
| Patient Advice | Do not drink alcohol or use products containing alcohol (mouthwash, cough syrup) during treatment and for 48 hours after the last dose. · Take exactly as prescribed; complete the full course even if you feel better. · May cause metallic taste, nausea, or dark urine (harmless). · Report any numbness, tingling, or weakness in arms/legs to your doctor immediately. · Avoid driving if you experience dizziness or confusion. |