Selamectin disables parasites by replacing glutamate in their muscle synapses; glutamate is the amino acid that normally interacts with the receptors that open chloride channels into the muscle. Selamectin interferes with this process; it activates the chloride current without desensitization, allowing chloride ions to enter the nerve cells and causing neuromuscular paralysis, impaired muscular contraction, and eventual death. The substance fights both internal and surface parasitic infection. Absorbed into the body through the skin and hair follicles, it travels through the bloodstream, intestines, and sebaceous glands; parasites ingest the drug when they feed on the animal's blood. Selamectin has high safety ratings, with less than 1% of pets displaying side effects. In cases where side-effects do occur, they most often include passing irritation or hair loss at the application site.
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