Pharmacodynamic ivermectin mainly has a good anthelmintic effect on nematodes and surface arthropods in vivo. Its anthelmintic mechanism is to promote the release of γ-aminobutyric acid (GABA) from presynaptic neurons, thereby opening GABA-mediated chloride channels. Ivermectin is also selective and high-affinity for glutamate-mediated chloride channels located near GABA-mediated sites in invertebrate nerve and muscle cells, thereby interfering with signal transmission between neuromuscular muscles and relaxing and paralyzing the parasite, resulting in parasite death or expulsion from the body. The inhibitory interneurons and excitatory motoneurons of C. elegans are their sites of action, while the site of action of arthropods is the neuromuscular junction. It is also effective against arthropods, such as fly maggots, mites, and lice. adult Coronaria dentata and immature parasites in pigs, is also extremely effective for Trichinella spiralis in the intestine (ineffective for intramuscular Trichinella spiralis), and also has a good control effect on pig blood lice and Sarcoptes scabiei. It is ineffective against trematodes and tapeworms.
The pharmacokinetics of ivermectin vary markedly depending on the animal species, dosage form, and route of administration. The bioavailability of subcutaneous injection is higher than that of oral administration, but oral administration is more rapidly absorbed than subcutaneous injection. After absorption, it can be well distributed to most tissues, but it is not easy to enter the cerebrospinal fluid. The apparent volume of distribution in sheep and pigs is 4.6 and 4 L/kg, respectively. It has a long half-life in most animals, 2 to 7 and 0.5 days in sheep and pigs, respectively. This product is metabolized in the liver, mainly hydroxylated in sheep, and mainly methylated in pigs. It is mainly excreted in the feces and less than 5% is excreted unchanged or as metabolites in the urine. In lactating dams, 5% of the dose is excreted in the milk.