Ronidazole
5-nitroimidazole compound
Also known as: Belga · Ridsol-S · Ronivet · Ronizol · Turbosol · Tricho Plus · Trichocure · Trichorex · ronidazolum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| treatment of T. foetus infections | 30 mg/kg PO q24h | PO | q24h | 14 days | 🌎 NA |
- treatment of T. foetus infections: Likely to be most effective in resolving diarrhea and eradicating T. foetus infection. Must be given in capsule form due to bitter taste.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ronidazole is a potent 5-nitroimidazole antibiotic and antiprotozoal agent. While structurally related to metronidazole, it exhibits superior efficacy against certain resistant protozoa.
- Primarily utilized off-label in veterinary medicine for the eradication of Tritrichomonas foetus infections in cats, a notorious cause of chronic large bowel diarrhea.
- Also employed in avian medicine to treat trichomoniasis (canker) in non-food birds (e.g., pigeons, finches).
Clinical Pearl: Due to its extremely bitter taste and potential human health risks (suspected carcinogen), it must be carefully compounded into intact gelatin capsules. It is strictly prohibited for use in food-producing animals.
Mechanism of action
Ronidazole is a prodrug that requires activation by protozoal organelles called hydrogenosomes.
- Inside the hydrogenosome, the drug is reduced → forms polar autotoxic anion radicals.
- These highly reactive radicals bind to and disrupt protozoal DNA → inhibition of nucleic acid synthesis → cell death.
Note: While it shares this mechanism with metronidazole, ronidazole often retains activity against metronidazole-resistant T. foetus strains, though resistance to ronidazole has been documented.
Safety & warnings
Contraindications
- Hypersensitivity to ronidazole or other 5-nitroimidazoles (e.g., metronidazole)
- Food-producing animals (FDA prohibited)
- Pregnant or nursing cats (safety not established; use with extreme caution)
Adverse effects
- Neurotoxicity (lethargy, anorexia, ataxia, nystagmus, seizures, behavior changes)
- Gastrointestinal effects (anorexia, vomiting)
- Carcinogenic potential (tumors in mice and rats)
- Testicular toxicity (reported in dogs)
Precautions
Human Safety Warnings
- Carcinogenic Potential: Demonstrated to be carcinogenic in mice. Humans should avoid contact with this compound or with animal waste from treated patients.
- Compounding: Must be safely compounded using a biological safety cabinet to protect the compounder from drug exposure.
- Administration: Wear disposable gloves when administering and when handling litter boxes.
Veterinary Precautions
- Neurotoxicity: Reversible neurotoxicity can occur. Incidence appears higher at 50 mg/kg twice daily, but can occur at lower doses.
- Regulatory: The FDA strictly prohibits this drug for use in food animals.
Drug interactions
May induce a disulfiram-like reaction (nausea, vomiting, cramps)
May decrease the metabolism of ronidazole and increase the likelihood of dose-related side effects
May decrease the metabolism of ronidazole and increase the likelihood of dose-related side effects
Ronidazole may increase the serum levels of cyclosporine
Ronidazole may increase the serum levels of tacrolimus
Ronidazole may increase the serum levels of fluorouracil and increase risk for toxicity
Ronidazole may increase lithium serum levels and increase risk for lithium toxicity
Reportedly may antagonize the therapeutic effects of metronidazole (and presumably ronidazole)
May increase the metabolism of ronidazole thereby decreasing blood levels
May increase the metabolism of ronidazole thereby decreasing blood levels
May increase the metabolism of ronidazole thereby decreasing blood levels
May prolong INR/PT; avoid concurrent use if possible or intensify monitoring
Monitoring
- Clinical efficacy (diarrhea improvement)
- Adverse effects (neurotoxicity, vomiting, anorexia)
- PCR testing (to confirm infection; note that negative results after treatment do not conclusively prove eradication)
Pharmacokinetics
Half-life
Absorption
Completely absorbed and bioavailable after oral dosing in cats.
Distribution
Volume of distribution (steady state) is about 0.7 L/kg.
Metabolism
Hepatic metabolism suspected (similar to metronidazole).
Elimination
Clearance is approximately 0.8 mL/kg/min.
Overdose
Overdoses can cause severe neurotoxicity, hemorrhage, and death (as reported in society finches consuming ronidazole in drinking water). Cats receiving 50 mg/kg twice daily have a greater incidence of neurotoxicity.
Treatment:
- Discontinue further therapy immediately.
- Treat supportively.
- Consider administering a GABA inhibitor, such as diazepam, to competitively inhibit GABA receptors in the CNS and control neurological signs.
Available products
Formulations
- Compounded capsules (from 100% bulk powder)
- 10% powder for drinking water (non-US veterinary product)
Veterinary
- 10% ronidazole powder (non-US, for pigeons; unsuitable for cats)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Compounded capsules should be stored in child-resistant, tight containers protected from light. Until further stability studies can be performed, capsules should be stored in the freezer. Aqueous solutions are not very stable and should be prepared fresh daily.
Client information
Important Safety Warning: Ronidazole is considered a potential carcinogen. Always wear disposable gloves when handling the medication or cleaning the litter box.
- Administration: Give the capsule whole by mouth. Do not open, crush, or break the capsules, as the powder is extremely bitter and poses an exposure risk to you.
- Schedule: Give exactly as directed by your veterinarian for the full 14 days. Do not skip doses. (Note: While some older protocols used twice-daily dosing, follow your vet's specific instructions carefully).
- Storage: Store the capsules in the freezer in a child-proof, light-resistant container.
- Hygiene: Double-bag all fecal waste and dispose of it in the regular trash.
- When to call the vet: Stop the medication and contact your vet immediately if your pet shows signs of toxicity, such as:
- Loss of appetite or vomiting
- Lethargy or behavior changes
- Unsteady walking, stumbling, or difficulty climbing stairs (ataxia)
- Rapid, involuntary back-and-forth eye movements (nystagmus)
- Seizures
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.