A Case of Isoniazid Intoxication in a Dog

A seven-month-old castrated male Chihuahua weighing 1.6 kg presented with generalized tonic-clonic seizure following ingestion of isoniazid. Emergency treatment with three doses of diazepam (total 1.5 mg/kg, intravenous [IV]) and phenobarbital (15 mg/kg IV) was administered. The seizure stopped after administration of propofol (constant rate infusion [CRI]; 0.2 mg/kg/min). Blood analyses showed mildly increased serum blood glucose concentration, hyperkalemia, and hyperphosphatemia. On suspicion of isoniazid toxicity, activated charcoal (1 g/kg, orally), lipid emulsion (CRI; 9 mL/hr), and pyridoxine hydrochloride (70 mg/kg IV) were added to the treatment regimen. Twelve hours after presentation, the dog showed increased serum liver enzyme activities, serum blood urea nitrogen, and creatinine concentrations indicating hepatic and renal failure. Twenty-two hours after presentation, blood analysis still revealed increased liver enzyme activities, blood urea nitrogen, and creatinine concentrations with low blood glucose concentration. Twenty-six hours after presentation, the dog's vital signs deteriorated and the owner elected for the dog to be euthanized. This is the first report of the clinical course of isoniazid toxicosis in a dog in South Korea. Furthermore, to our best knowledge, this is the first report where secondary multiple organ failure was observed due to isoniazid toxicosis. Clinicians should be aware of the possibility of isoniazid toxicosis in dogs. Rapid initiation of treatment after clinical recognition is warranted in such cases.