Is Metronidazole safe for dogs and cats?

Metronidazole is widely used in dogs for treatment of Giardia, anaerobic infections, inflammatory bowel disease, and Clostridioides difficile diarrhea. At standard therapeutic doses (15–25 mg/kg twice daily), it is generally well-tolerated with primary adverse effects of GI upset. The principal veterinary concern is metronidazole neurotoxicity — a syndrome of acute vestibular dysfunction, cerebellar signs, nystagmus, ataxia, head tilt, and seizures that occurs at doses exceeding 60–70 mg/kg or with prolonged high-dose therapy. Neurotoxicity is attributed to GABA inhibition in the cerebellar and brainstem regions; cerebellar Purkinje cell degeneration is found on post-mortem. Diazepam administration has been reported to speed recovery from metronidazole neurotoxicity. Clinicians should avoid doses exceeding label recommendations and limit duration of therapy; recovery from neurotoxicity is generally complete if treatment is stopped promptly.

Metronidazole is used in cats for Giardia, tritrichomonad infections, IBD, and anaerobic bacterial infections. Cats appear somewhat more sensitive to metronidazole neurotoxicity than dogs; the vestibular syndrome (ataxia, nystagmus, disorientation) can occur at doses as low as 58 mg/kg or with prolonged use at lower doses. The palatability of liquid metronidazole is poor in cats, contributing to stress-induced anorexia and difficulty completing treatment courses. Cats also experience the same GI adverse effects (nausea, hypersalivation, anorexia) as dogs. Metronidazole benzoate oral preparations have improved palatability for cats. Standard doses for feline Giardia are 15–25 mg/kg once daily; courses should be kept to 5–7 days when possible. Recovery from neurotoxicity is generally complete after drug discontinuation.