Just Ask the Expert: The best way to treat ivermectin toxicosis
Q. Is there an antidote for ivermectin toxicosis in dogs and cats? What is the recommended treatment protocol?
What is considered toxic?The toxic dose of ivermectin in dogs and cats ranges between 0.1 and 2.5 mg/kg (100 and 2,500 μg/kg). Dog breeds with defective P-glycoprotein (a recessive mutation in the ABCB1 gene, previously called the MDR1 gene), can experience toxic effects at the lower end of the toxic dose range because of higher concentrations of certain drug being allowed to cross the blood-brain barrier. These breeds include collies, border collies, Australian shepherds, and Shetland sheepdogs.
If the patient is alert enough, decontamination with activated charcoal is indicated and may need to be repeated every four to six hours as ivermectin undergoes enterohepatic circulation. There is anecdotal evidence that tremors may respond to benzodiazepines or methocarbamol.
Recently, use of an intravenous lipid emulsion (ILE) has shown success in ameliorating clinical signs in patients with ivermectin toxicosis. The mechanism of action of lipid emulsion is not completely understood but is thought to provide a "lipid sink" that allows lipophilic agents to partition out of the plasma and accelerate elimination. The most commonly used ILE is a 20% emulsion with a tonicity of about 800 mOsm/L, which allows administration through a peripheral vein.
The suggested administration protocol is as follows:
Most patients with ivermectin toxicosis respond well to supportive care and return to normal within 48 to 72 hours. Resolution may be more rapid in patients treated with ILE therapy.
This expert answer was provided by Jennifer L. Garcia, DVM, DACVIM, Sugar Land Veterinary Specialists, Houston, Texas.
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