Eprinomectin is 4"-deoxy-4"-epiacetylamino-avermectin B1. It is a semi-synthetic member of the avermectin family of macrocyclic lactones and consists of a mixture of two homologous components, B1a (not less than 90%) and B1b (not more than 10%), which differ by a single methylene group at C26. Eprinomectin is a member of the macrocyclic lactone class of endectocides which have a unique mode of action. Compounds of the class bind selectively and with high affinity to glutamate-gated chloride ion channels which occur in invertebrate nerve and muscle cells. This leads to an increase in the permeability of the cell membrane to chloride ions with hyperpolarization of the nerve or muscle cell, resulting in paralysis and death of the parasite. Compounds of this class may also interact with other ligand-gated chloride channels, such as those gated by the neurotransmitter gamma-aminobutyric acid (GABA). Molecular studies indicate that these drugs interact strongly not only with ligand-gated ion channels, the mode-of action receptors of nematodes and arthropods, but also with efflux ABC transporters. The margin of safety for compounds of this class is attributable to the fact that mammals do not have glutamate-gated chloride channels, the macrocyclic lactones have a low affinity for other mammalian ligand-gated chloride channels and they do not readily cross the blood-brain barrier. IVOMEC EPRINEX (eprinomectin) Pour-On is indicated for the treatment and control of gastrointestinal roundworms (including inhibited Ostertagia ostertagi), lungworms, grubs, sucking and biting lice, chorioptic and sarcoptic mange mites, and horn flies in beef and dairy cattle of all ages, including lactating dairy cattle.