The avermectins are a series of drugs used to treat parasitic worms. Anthelmintics derived from the avermectins include ivermectin, selamectin, doramectin, and abamectin. The avermectins block the transmission of electrical activity in invertebrate nerve and muscle cells mostly by enhancing the effects of glutamate at the invertebrate-specific glutamate-gated chloride channel, with minor effects on gamma-aminobutyric acid receptors. This causes an influx of chloride ions into the cells, leading to hyperpolarisation and subsequent paralysis of invertebrate neuromuscular systems; comparable doses are not toxic for mammals because they do not possess glutamate-gated chloride channels.