1. Clinical Overview
A fixed-dose combination (FDC) antibacterial and antiprotozoal agent. Metronidazole is a nitroimidazole derivative effective against anaerobic bacteria and protozoa. Norfloxacin is a second-generation fluoroquinolone antibiotic with broad-spectrum activity against Gram-negative and some Gram-positive bacteria. This combination is primarily used for the treatment of mixed aerobic-anaerobic infections, particularly in the gastrointestinal and genitourinary tracts. The FDC was banned by the Indian government in 2018 due to concerns over irrationality and increased risk of adverse effects, but some brands may still be available in the market under specific circumstances or prior stocks.
| Onset | Duration | Bioavailability |
|---|---|---|
| Metronidazole: 1-2 hours. Norfloxacin: 1-2 hours. | Metronidazole: 8-12 hours. Norfloxacin: 12 hours. | Metronidazole: ~80% (oral). Norfloxacin: 30-40% (oral). |
2. Mechanism of Action
The combination provides a synergistic or additive effect against mixed infections involving both aerobic and anaerobic organisms. Metronidazole enters microbial cells and is reduced by nitroreductases to form toxic nitro radical anions that damage DNA and other critical macromolecules. Norfloxacin inhibits bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, enzymes essential for DNA replication, transcription, and repair, leading to bactericidal activity.
3. Indications & Uses
- Acute bacterial diarrhea (presumed mixed infection)
- Traveler's diarrhea
- Pelvic Inflammatory Disease (PID) - as part of combination therapy (though not first-line)
- Mixed aerobic-anaerobic infections of the gastrointestinal tract.
4. Dosage & Administration
Adult Dosage: One tablet (Metronidazole 100mg + Norfloxacin 100mg) twice daily. Typically prescribed for 5-7 days. The dose is lower than standard monotherapy doses of either drug.
Administration: Take on an empty stomach, at least 1 hour before or 2 hours after meals, to maximize norfloxacin absorption. Swallow whole with a full glass of water. Maintain adequate hydration. Do not take with dairy products, calcium-fortified juices, antacids, or iron/zinc supplements; separate by at least 2-4 hours.
5. Side Effects
Common side effects may include:
- Nausea
- Metallic taste in mouth (metronidazole)
- Headache
- Dizziness
- Dry mouth
- Abdominal discomfort
- Diarrhea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Alcohol (Ethanol) | Disulfiram-like reaction with metronidazole (flushing, tachycardia, nausea, vomiting). | Major |
| Warfarin and other Coumarin anticoagulants | Metronidazole inhibits metabolism, increasing anticoagulant effect and risk of bleeding. | Major |
| Lithium | Metronidazole may increase lithium levels, risk of toxicity. | Major |
| Antacids, Sucralfate, Divalent/Trivalent cations (Ca, Mg, Al, Fe, Zn) | Severely reduce absorption of norfloxacin via chelation. | Major |
| Theophylline | Norfloxacin may inhibit metabolism, increasing theophylline levels and risk of toxicity. | Moderate |
| Cyclosporine | Norfloxacin may increase cyclosporine levels. | Moderate |
| NSAIDs (e.g., Ibuprofen) | May increase risk of CNS stimulation and seizures when combined with fluoroquinolones. | Moderate |
| Cimetidine | May reduce metabolism of metronidazole, increasing its levels. | Moderate |
| Phenobarbital, Phenytoin | May increase metabolism of metronidazole, reducing its efficacy. | Moderate |
7. Patient Counselling
- DO take the tablet on an empty stomach with a full glass of water.
- DO complete the full course of therapy, even if you feel better.
- DO maintain good hydration.
- DO separate this medicine from antacids, vitamins/minerals (iron, calcium, zinc), or dairy products by at least 2-4 hours.
- DO NOT consume alcohol or products containing alcohol (syrups, tonics) during treatment and for at least 3 days after stopping.
- DO NOT take this medicine if you are pregnant, planning pregnancy, or breastfeeding.
- DO NOT give this medicine to children or adolescents.
8. Toxicology & Storage
Overdose: Nausea, vomiting, ataxia, seizures, peripheral neuropathy (metronidazole). Nausea, vomiting, dizziness, headache, tremors, seizures, acute renal failure (norfloxacin). Prolonged QT interval and arrhythmias are possible with large overdoses.
Storage: Store below 30°C, in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.