Metronidazole (Flagyl) Toxicity in Cats

Metronidazole (Flagyl) is a commonly used and very effective antibiotic. It is most frequently used to treat gastrointestinal parasites, primarily Giardia. It has also been used to treat severe infections, usually in combination with other antibiotics. Unfortunately, as with all drugs, toxicity and adverse effects can occur. However, toxicity from metronidazole is uncommon and is generally associated with prolonged use (many weeks) or high doses of the drug. Animals with underlying liver disease are more prone to metronidazole toxicity. Toxic levels of metronidazole affect the brain and equilibrium.

What to Watch For

• Not eating
• Vomiting
• Staggering or difficulty walking
• Involuntary and constant eye movements (nystagmus)
• Lethargy
• Seizures

Diagnosis

The diagnosis of metronidazole toxicity is based on physical exam findings as well as a history of recent drug administration. Blood tests for toxic levels of metronidazole are not very effective and are rarely done.

Treatment

The initial treatment for metronidazole toxicity is to stop administration of the drug immediately. Depending on the severity of the toxicity, some pets may need to be hospitalized with constant intravenous fluids. Medication to eliminate vomiting may also be needed. Blood work may be necessary to evaluate the function of the liver and kidneys. There is no specific antidote for metronidazole toxicity and recovery may take 1-2 weeks. Some pets severely affected by metronidazole toxicity may not survive.

Home Care and Prevention

There is no home care for metronidazole toxicity. If you suspect that metronidazole is responsible for illness in your pet, consult your veterinarian before discontinuing medication; you may need another treatment for the initial infection for which the metronidazole was prescribed.

Give all medications as prescribed by your family veterinarian. Do not give additional doses unless specifically directed by your veterinarian.