Ivermectin is a macrolide antibiotic produced from a fungus first isolated from a soil sample in Japan - Streptomyces avermitilis . The avermectins are a class of chemicals that have a novel mode of action against nematode and arthropod parasites. Ivermectin is a mixture of the 22, 23-dihydro derivative of avermectin B1. Ivermectin was licensed for use in the United States in 1983. Dogs are usually intoxicated with ivermectin from the inappropriate, extra-labeled use of cattle, sheep or horse product.
Adult cats seem to be less sensitive.
Ivermectin is a GABA agonist, which will increase the effects of inhibitory neural pathways in the CNS leading to depression and stupor. GABA is a major inhibitory neurotransmitter. This difference in location of GABA receptor may be the reason for the large margin of safety of ivermectin-containing products in mammals. GABA binds to the GABA receptor-chloride channel complex of postsynaptic neuronal membranes causing an influx of chloride ions. The influx of chloride ions hyperpolarize the neuronal membrane making them less excitatory and decreasing nerve transmission.