Metronidazole
Metronidazole
Brand names:Flagyl, MetroGel
A nitroimidazole antibiotic and antiprotozoal agent with potent activity against anaerobic bacteria and certain protozoa. In TCCC and deployment medicine, metronidazole is paired with other antibiotics for anaerobic coverage in intra-abdominal injuries and used for treatment of giardiasis and amebic infections in austere environments.
Pharmacology and Actions
Metronidazole is reduced in anaerobic bacteria and protozoa to reactive intermediates that damage DNA and inhibit nucleic acid synthesis. The drug requires the anaerobic environment to activate, which is why it has selective activity against anaerobes and protozoa. Spectrum includes Bacteroides, Clostridium (including C. difficile), Giardia lamblia, Entamoeba histolytica, and Trichomonas vaginalis. Activity against aerobic and facultative organisms is negligible.
Indications
- Anaerobic coverage in intra-abdominal injuries (typically combined with cephalosporin or carbapenem)
- Clostridioides difficile colitis (oral route)
- Giardiasis and amebiasis in deployment medicine and traveler's diarrhea
- Bacterial vaginosis and trichomoniasis
- Dental and oral anaerobic infections
- Helicobacter pylori eradication (as part of triple therapy)
Absolute Contraindications
- Known metronidazole or nitroimidazole allergy
- First-trimester pregnancy (relative)
- Concurrent alcohol use (disulfiram-like reaction)
- Severe hepatic impairment without dose adjustment
Precautions and Side Effects
The disulfiram-like reaction with alcohol is the hallmark adverse effect; patients must avoid all alcohol during therapy and for 48 to 72 hours after the last dose. Metallic taste, nausea, and GI upset are common. Peripheral neuropathy and CNS effects (encephalopathy, seizures, cerebellar dysfunction) can occur, particularly with prolonged or high-dose therapy. Carcinogenicity has been demonstrated in animal studies; relevance to short-course human use is unclear but limits long-term prophylactic use.
Adult Dosing
Pediatric Dosing
Pediatric dosing varies by indication. Anaerobic infection: 7.5 mg/kg PO/IV every 6 hours (maximum 4 grams/day). Giardiasis: 15 mg/kg/day PO divided every 8 hours for 5 to 7 days. Pediatric tactical use is uncommon; consult medical control.
Pharmacokinetics
Peak Effect: PO: 1 to 2 hours. IV: end of infusion.
Duration: 6 to 8 hours per dose; requires q6 to q8h dosing for sustained levels
Storage and Handling
Store tablets and capsules at controlled room temperature (15 to 30 degrees Celsius). Protect from light. IV bags are ready to infuse and stable at room temperature when protected from light. Topical preparations have specific storage per manufacturer.
Reconstitution:
Tablets and IV ready-to-use bags require no reconstitution. The IV preparation is supplied as 500 mg in 100 mL premix bag.
TCCC and TECC Role
Metronidazole is the anaerobic coverage drug paired with ceftriaxone or ertapenem in TCCC and prolonged field care for casualties with abdominal trauma, perineal injuries, or contaminated extremity wounds with significant tissue devitalization. The drug is not used as monotherapy for wound prophylaxis; it lacks aerobic coverage. In deployment medicine, metronidazole has additional roles for traveler's diarrhea complicated by Giardia or amebiasis, and for management of C. difficile colitis when it complicates antibiotic-treated casualties.
Metronidazole is the drug for anaerobes. It is not a stand-alone wound antibiotic and should not be used as monotherapy for prophylaxis or treatment of wound infections. Its operational role in TCCC is the second drug in combination therapy for abdominal trauma and complicated soft tissue injuries with anticipated anaerobic contamination. In deployment kits, the oral formulations are valued for traveler's diarrhea protozoal coverage and for managing the C. difficile complications that follow other antibiotic use. Patients must be educated about the alcohol interaction.
Using metronidazole as a sole wound prophylaxis agent. The drug lacks activity against aerobic gram-positive and gram-negative organisms, which are the predominant wound contaminants. Metronidazole pairs with a cephalosporin or carbapenem for full coverage. The other common error is failing to warn the casualty about alcohol; the disulfiram reaction can be severe and is preventable with patient education.
This drug profile is provided as educational reference material for trained medical providers. It is not medical advice, not a substitute for formal training, and not a substitute for current published guidelines or medical direction.
Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances are subject to additional handling, accountability, and documentation requirements per DEA and state law. Always verify dosing, indications, contraindications, and route of administration against current published guidelines and your local protocols before administration.
If this content is being viewed during a medical emergency, call 911 immediately and follow the direction of your local emergency dispatch and medical control. Do not use this reference as a substitute for emergency medical services.
Drug information evolves. Last reviewed dates and source citations are provided for each entry. Confirm currency against the cited source before clinical use.
Penn Tactical Solutions publishes this reference for educational purposes. PTS does not provide medical direction and does not assume responsibility for clinical decisions made in the field. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Educational reference for trained medical providers. Not medical advice. Not a substitute for formal training, current published guidelines, or medical direction. Drug administration is governed by your scope of practice, agency standing orders, medical director protocols, and applicable state and federal regulations. Controlled substances require additional storage, accountability, and documentation per DEA and state law.
In a medical emergency, call 911. This reference is not a substitute for emergency medical services.
Verify dosing, indications, and contraindications against current published guidelines and your local protocols before administration. Confirm content currency against the source citation. Penn Tactical Solutions does not provide medical direction. Clinical responsibility rests with the administering provider, their medical director, and their agency.
Metronidazole
| IV/IO | Intra-abdominal infection: 500 mg IV every 8 hours (loading dose 15 mg/kg may be used). Infuse over 30 to 60 minutes. C. difficile severe: 500 mg IV every 8 hours when oral route not available. (Immediate after infusion) |
| PO | C. difficile colitis: 500 mg PO every 8 hours for 10 to 14 days (vancomycin PO is now preferred). Giardiasis: 250 to 500 mg PO every 8 hours for 5 to 7 days. Amebiasis: 500 to 750 mg PO every 8 hours for 5 to 10 days. Trichomoniasis: 2 grams PO single dose. (1 to 2 hours (high oral bioavailability)) |