1. Clinical Overview
Ornidazole is a second-generation 5-nitroimidazole derivative antimicrobial and antiprotozoal agent. The 500mg/100ml formulation is a sterile solution for intravenous infusion, primarily used in hospital settings for the management of severe anaerobic and protozoal infections where oral therapy is not feasible. It is bactericidal and trichomonacidal, with a broad spectrum of activity against anaerobic bacteria and protozoa like Giardia and Trichomonas.
| Onset | Duration | Bioavailability |
|---|---|---|
| Peak plasma concentrations are achieved at the end of a 30-minute intravenous infusion. | Approximately 12-14 hours, supporting a twice-daily (BID) dosing regimen. | Approximately 90% following oral administration. For IV formulation, bioavailability is considered 100%. |
2. Mechanism of Action
Ornidazole is a prodrug. Its nitro group is reduced intracellularly by low-redox potential electron transport proteins (ferredoxin or flavodoxin) found in anaerobic microorganisms. This reduction forms cytotoxic, short-lived intermediates (nitroso and hydroxylamine derivatives) that cause DNA damage.
3. Indications & Uses
- Severe Amoebiasis (intestinal and extra-intestinal, including liver abscess)
- Symptomatic Trichomoniasis (when oral therapy is not possible)
- Giardiasis (severe cases requiring hospitalization)
- Anaerobic bacterial infections (e.g., Bacteroides fragilis, Clostridium spp.) causing peritonitis, intra-abdominal abscesses, pelvic inflammatory disease, post-surgical infections, and brain abscess.
4. Dosage & Administration
Adult Dosage: 500 mg (100 ml) intravenous infusion every 12 hours (BID). For surgical prophylaxis: A single 500 mg IV dose 1 hour pre-operatively.
Administration: For IV infusion only. Must be diluted before administration. The 100 ml solution (500 mg) should be infused slowly over 30-60 minutes. Can be diluted with 0.9% Sodium Chloride, 5% Dextrose, or Ringer's Lactate. Do not mix with other medications in the same IV line. The solution is photosensitive; protect from light during storage and infusion.
5. Side Effects
Common side effects may include:
- Nausea
- Metallic or bitter taste in mouth
- Headache
- Dizziness
- Injection site reactions (pain, phlebitis)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin and other Coumarin Anticoagulants | Ornidazole may potentiate anticoagulant effect by inhibiting metabolism, increasing INR and bleeding risk. | Major |
| Alcohol (Ethanol) | Although weaker than with metronidazole, a disulfiram-like reaction (flushing, tachycardia, nausea) is possible. Strictly avoid. | Major |
| Phenobarbital, Phenytoin, Rifampicin | Enzyme inducers may increase metabolism of ornidazole, reducing its plasma concentration and efficacy. | Moderate |
| Cimetidine, Ketoconazole, Fluconazole | CYP450 inhibitors may decrease metabolism of ornidazole, increasing its plasma concentration and risk of toxicity. | Moderate |
| Lithium | May increase lithium levels and risk of toxicity. Monitor serum lithium levels. | Moderate |
| Vecuronium and other non-depolarizing muscle relaxants | Ornidazole may potentiate neuromuscular blockade. | Moderate |
7. Patient Counselling
- Complete the full course of treatment as prescribed, even if you feel better.
- Inform your doctor about all other medicines, vitamins, or herbal supplements you are taking.
- Do not consume any alcohol during treatment and for at least 2 days after stopping the medicine.
- If you are using the oral form, take it with food to minimize stomach upset.
8. Toxicology & Storage
Overdose: Symptoms may include severe nausea, vomiting, ataxia, seizures, and peripheral neuropathy. CNS depression may occur.
Storage: Store below 25°C. Do not freeze. Protect from light. The unopened vial/bottle should be kept in the outer carton. After dilution, the infusion solution should be used immediately. Do not store partially used vials. Keep out of reach of children.