Metronidazole

Antibiotic, Antiprotozoal (Systemic Drug)

Prescriber Highlights

• Injectable and oral antibacterial and antiprotozoal agent

• Main side effects include neurologic disorders, lethargy, weakness, hepatotoxicity

• Bitter tasting; may be more palatable when compounded

Uses, Indications

• Used for treatment of Giardia spp in both dogs and cats, in addition to several other parasitic infections (eg, trichomonads, Balantidium coli) and anaerobic enteric and systemic infections 

• Commonly used for perioperative surgical prophylaxis when anaerobic infections (eg, colon, periodontal) are likely

• Has some inhibitory actions on cell-mediated immunity that may play a role in its use for treatment of inflammatory bowel disease

Contraindications, Precautions, Warnings

• Contraindications

Patients with a history of hypersensitivity to metronidazole or nitroimidazole derivatives

• Precautions

Not recommended for use in severely debilitated, pregnant, or nursing patients; use with caution in patients with hepatic dysfunction

• Warnings

Total daily dose should not exceed 65 mg/kg because of risk for neurotoxicity

Side Effects

• Neurologic disorders, lethargy, weakness, neutropenia, hepatotoxicity, hematuria, nausea, anorexia, vomiting, and diarrhea have been reported in dogs

• Neurologic toxicity in dogs may occur with acute high doses but is more common with chronic moderate- to high-dose therapy

• Vomiting, inappetence, and hepatotoxicity can occur in cats undergoing metronidazole therapy 

• Central nervous toxicity, although rare, can also occur in cats

Drug Interactions

• Cimetidine may decrease the metabolism of metronidazole, increasing the possibility of dose-related side effects

• Cyclosporine levels may increase when combined with metronidazole therapy

• Fluorouracil (5-FU) may result in increased 5-FU levels and possible toxicity

• Phenobarbital or phenytoin may increase the metabolism of metronidazole, decreasing blood levels

• Metronidazole may prolong prothrombin time in patients receiving warfarin or other coumarin anticoagulants

Monitoring

• Clinical efficacy, side effects

Client Information

• Clients should pay close attention to any neurologic abnormalities

Dosage Forms

• Metronidazole oral tablets: 250 mg, 500 mg

• Metronidazole oral solution: 5 mg/mL

—Compiled and summarized from Plumb’s Veterinary Drugs by Shannon Palermo, VMD

Information about this drug was adapted from Plumb’s Veterinary Drugs. Further details and more therapeutics can be found with a subscription at plumbsveterinarydrugs.com.