Category: Side Effects and Interactions

Pharmacovigilance, Adverse Drug Events & Toxicological Management

While ivermectin is exceptionally well-tolerated at microgram heartworm prophylactic levels, pharmacovigilance monitoring is critical when administering elevated dosages for mange or when treating animals with unknown genetic backgrounds. Adverse drug reactions range from mild, transient lethargy to life-threatening neurotoxicosis.

In dogs with functional P-glycoprotein efflux pumps, the blood-brain barrier effectively excludes ivermectin from the central nervous system. When toxic concentrations penetrate into the brain (either via massive accidental overdose or ABCB1 gene mutations), the drug binds to cerebral GABA receptors, increasing inhibitory neurotransmission. Clinical manifestations progress predictably: bilateral mydriasis (dilated pupils), ataxia (wobbly gait), muscle tremors, hypersalivation, blindness, bradycardia, recumbency, and coma.

Drug-drug interactions present an additional clinical hazard. Concurrently administering ivermectin with potent P-glycoprotein inhibitors (such as ketoconazole, itraconazole, cyclosporine, spinosad, or erythromycin) impairs normal drug clearance and can precipitate neurotoxicity even in genetically normal dogs. Suspected toxicity requires immediate emergency veterinary intervention, including intravenous lipid emulsion (ILE) therapy to sequester the lipophilic avermectin molecules.