Ivermectin has been historically used as an antiparasitic. For worms and mites and lice. Mammals have a blood brain barrier that this drug does not cross except in really high doses. But it has a neurotoxic effect on simple critters like lice and mites etc. Veterinarians use it alot because its pretty safe. It also happens to have strong antiviral activity against flu and sars cov 2 and zika, hiv, dengue fever, alot of shit. It seems to also have some antibiotic activity against some bacteria like staphylococcus, leprosy, and tuberculosis.