Decontamination is rarely possible in these cases because of the rapid onset of signs (30 minutes to 2 hours*). If the animal is clinically normal, emesis can be attempted in the practice. Emesis should not be induced in patients with clinical abnormalities because of risk for aspiration pneumonia. If an animal is clinically affected and has ingested a large number of pills, gastric lavage may be necessary under anesthesia (with a protected airway).
With isoniazid toxicosis, pyridoxine (vitamin B6) should be administered promptly. Pyridoxine is considered the antidote for this toxicosis because it is a direct antagonist of isoniazid and will quickly reverse the clinical signs. Dosing should be based on the equivalent amount (mg for mg) of isoniazid that was ingested. If the amount of isoniazid ingested is unknown, the suggested dose is 71 mg/kg (Table).
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Other treatments include anticonvulsant therapy, fluid therapy, and supportive care. Immediate IV access should be established. If the patient presents with grand mal seizures, anticonvulsants should be implemented until pyridoxine can be given; however, anticonvulsant therapy is often ineffective until pyridoxine is administered. A balanced maintenance crystalloid should be administered to enhance urinary excretion of isoniazid, to help perfuse the patient, and to minimize acute kidney injury secondary to myoglobinuria. Other treatments include thermoregulation, blood glucose and serum chemistry profile monitoring, and supportive care. Liver enzymes should be rechecked 3 to 5 days after discharge.
Overall, the prognosis for isoniazid toxicosis is fair if pyridoxine can be administered quickly. Although this human medication may not be a common toxicant ingested by dogs, it can be life-threatening. In dogs that fail to respond to therapy or have significant CNS signs, the prognosis is guarded to grave.