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.
Adult: 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.
Note: 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.
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.
Pregnancy: CONTRANDICATED. Metronidazole is FDA Pregnancy Category B, but data on early pregnancy is conflicting. Norfloxacin is Category C (risk of arthropathy in animal studies). The combination is not recommended due to potential risks. Use only if potential benefit justifies the risk to the fetus, and avoid in first trimester.
Driving: May impair mental and/or physical abilities. Dizziness, lightheadedness, confusion, and visual disturbances have been reported. Patients should be cautioned about driving or operating machinery until their response is known.
| 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 |
Same composition (Metronidazole (100mg) + Norfloxacin (100mg)), different brands: