Ronidazole — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Cat	PO	30 mg/kg	q24h	Duration: 14 days Notes: Administer with food to reduce gastrointestinal upset. Compounded suspension is often used.
Pigeon	PO (in water or by gavage)	25-50 mg/kg	q24h	Duration: 5-7 days Notes: Often administered via drinking water at 400 mg/L for 7 days.
Poultry (chickens, turkeys)	PO (in feed or water)	200-400 ppm in feed	Continuous	Duration: 7-10 days Notes: Not approved in many countries; use with caution.
Rabbit	PO	20-30 mg/kg	q24h	Duration: 5-7 days Notes: Off-label use; monitor for neurological signs.

Clinical Indications & Species Uses

General Indications

Treatment of infections caused by susceptible anaerobic bacteria and protozoa, particularly Trichomonas spp. and Giardia.

Cat (Feline)

Trichomoniasis (Trichomonas foetus) – treatment of choice
Giardiasis (off-label)

Avian & Poultry

Trichomoniasis (Trichomonas gallinae) in pigeons and other birds
Histomoniasis (blackhead) in poultry (off-label)

Exotic & Other Species

Trichomoniasis in reptiles (off-label)
Giardiasis in small mammals (off-label)

Pharmacology & Mechanism of Action

Drug Class: Nitroimidazole antimicrobial | Pharmacological Group: Antiprotozoal, antibacterial

Mechanism of Action: Ronidazole is a nitroimidazole derivative that exerts its antimicrobial effect by entering susceptible microbial cells, where its nitro group is reduced by ferredoxin-like electron transport proteins to form reactive cytotoxic intermediates. These intermediates damage microbial DNA and other critical cellular components, leading to cell death. It is particularly effective against anaerobic bacteria and certain protozoa, including Trichomonas spp., Giardia, and Histomonas.

Pharmacodynamics: Ronidazole is primarily used for its antiprotozoal activity, especially against Trichomonas gallinae in pigeons and Trichomonas foetus in cats. It is also effective against Giardia and some anaerobic bacteria. Its activity is concentration-dependent and generally bactericidal/protozoacidal. Resistance can develop through reduced nitroreductase activity.

⚡ Pharmacokinetics Summary

Absorption: Ronidazole is well absorbed after oral administration in most species. In cats, oral bioavailability is approximately 100%.

Distribution: It is widely distributed throughout the body, including tissues and body fluids. It crosses the blood-brain barrier and placental barrier. Protein binding is low.

Metabolism: Ronidazole is extensively metabolized in the liver, primarily by oxidation and conjugation. Metabolites are excreted in urine and feces.

Excretion: Excretion is primarily renal, with metabolites and some unchanged drug eliminated in urine. Biliary excretion also occurs.

Half-Life: In cats, the elimination half-life is approximately 5-6 hours. In other species, it may vary.

Bioavailability: Oral bioavailability is high, approximately 100% in cats and likely similar in other monogastric species.

Protein Binding: Low (<20%)

Available Formulations & Strengths

Oral Tablet (compounded) 50 mg, 100 mg (compounded) (PO)

Oral Suspension (compounded) 10 mg/mL, 20 mg/mL (PO)

Powder for oral solution (veterinary) Varies (e.g., 10% powder) (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to nitroimidazoles
Pregnancy (especially first trimester) unless benefits outweigh risks
Lactation (excreted in milk)
Severe hepatic impairment
Use in food animals where withdrawal times cannot be met

Warnings & Clinical Precautions:

Use with caution in animals with neurological disorders.
May cause immunosuppression with prolonged use.
In cats, neurological signs (ataxia, tremors) can occur at high doses or prolonged therapy; discontinue if observed.
Not approved for use in food animals in many countries; extra-label use requires extended withdrawal times.
Handle with care; potential carcinogen in laboratory animals.

Adverse Effects & Reactions

Common:

Gastrointestinal upset (vomiting, diarrhea, anorexia)
Metallic taste (in humans handling drug)

Serious / Severe:

Neurotoxicity (ataxia, tremors, seizures, nystagmus)
Hepatotoxicity
Bone marrow suppression (with prolonged use)

Rare:

Allergic reactions
Peripheral neuropathy

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Warfarin and other anticoagulants	May enhance anticoagulant effect; monitor coagulation.	Moderate
Phenobarbital and other CYP inducers	May increase metabolism of ronidazole, reducing efficacy.	Moderate
Cimetidine	May decrease metabolism of ronidazole, increasing risk of toxicity.	Moderate
Alcohol (in animals, not typical)	Disulfiram-like reaction possible.	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Neurological signs (ataxia, tremors, seizures)
Vomiting
Anorexia
Lethargy
Hepatotoxicity

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids, anticonvulsants (e.g., diazepam) for seizures, and monitor liver function. In severe cases, hospitalization may be required.

Food Animal Withdrawal Times

🥩 Meat: 28 days🥛 Milk: 7 days🥚 Eggs: 14 days

Withdrawal times are not officially established for ronidazole in many countries; these are conservative estimates. Extra-label use in food animals requires extended withdrawal periods (e.g., 30 days for meat, 10 days for milk). Check local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C, excursions permitted to 15-30°C).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Compounded formulations may have different storage requirements; follow label.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; available as a compounded product or through foreign sources.

Extra-Label (Off-Label) Use: In the US, ronidazole is not FDA-approved for use in animals; it is used extra-label under AMDUCA. For food animals, a withdrawal time must be established by a veterinarian. In the EU, it is prohibited for use in food-producing animals.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Ronidazole is the treatment of choice for feline trichomoniasis caused by Tritrichomonas foetus. It is also used in pigeons for Trichomonas gallinae. Due to its potential for neurotoxicity, especially in cats, it should be used with caution and at the recommended dose. Compounded formulations are often necessary because commercial products are not widely available. In food animals, its use is highly restricted due to carcinogenic potential and lack of established withdrawal times. Always obtain a thorough history and perform diagnostic testing to confirm the causative organism before initiating therapy. Monitor for adverse effects, particularly neurological signs, and discontinue if they occur. Client education is important regarding handling of the drug (avoid skin contact, wear gloves) and proper disposal.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)