Metronidazole

Metronidazole In Dogs & Cats: Uses, Dosage and Side Effects

Overview

• Synthetic nitroimidazole with antibacterial and antiprotozoal activity.
• Its mechanism of action on protozoans is unknown.
• In bacteria, it appears to be reduced spontaneously under anaerobic conditions to compounds that bind to DNA and cause cell death.
• Spiramycin is a macrolide antibacterial that inhibits bacterial protein synthesis.

Uses of Metronidazole

• Treatment of anaerobic infections, including GI infections caused by Clostridia spp.
• Management of hepatic encephalopathy.
• Metronidazole may be used to treat chronic enteropathy due to potential effects on the immune system (modulation of cell-mediated immune responses). However, evidence of efficacy in cats and dogs is limited.

Dose of Metronidazole in Dogs and Cats

Dogs, Cats:

• Metronidazole: 7.5–25 mg/kg (standard dose 10–15 mg/kg) p.o. q12h. 10–15 mg/kg s.c., slow i.v. infusion q12h.
• The injectable solution may be given intrapleurally to treat empyema.
• Stomorgyl: 12.5 mg metronidazole + 23.4 mg spiramycin/kg p.o. (equivalent to 1 tablet/2 kg of Stomorgyl 2, 1 tablet/10 kg of Stomorgyl 10 and 1 tablet/20 kg of Stomorgyl 20) q24h for 5–10 days.

Side Effects of Metronidazole in Dogs and Cats

• Vomiting, CNS toxicity (nystagmus, ataxia, knuckling, head tilt and seizures), hepatotoxicity, neutropenia and haematuria.
• Excessive salivation/foaming is noted in some cats.
• Impaired sense of smell has been reported in explosive detection dogs (resolved following drug withdrawal).
• Prolonged therapy or pre-existing hepatic disease may predispose to CNS toxicity.

Contraindications of Metronidazole in Dogs and Cats

• Avoid use during pregnancy (may be a teratogen, especially in early pregnancy).
• Reduce the dose if the drug is used in animals with hepatic disease.

Some Notes:

• Phenobarbital or phenytoin may enhance the metabolism of metronidazole.
• Cimetidine may decrease the metabolism of metronidazole.
• Spiramycin should not be used concurrently with other antibiotics of the macrolide group as the combination may be antagonistic.
• It is absorbed well from the GI tract and diffuses into many tissues including bone, CSF and abscesses.
• Spiramycin (a constituent of Stomorgyl) is active against Gram-positive aerobes including Staphylococcus, Streptococcus, Bacillus and Actinomyces.
• Metronidazole is frequently used in combination with penicillin or aminoglycoside antimicrobials to extend the spectrum of activity.
• There is a greater risk of adverse effects with rapid i.v. infusion or high total doses.
• It is no longer used in dogs and cats for the treatment of giardiasis as fenbendazole and others are preferred.