What is the general mechanism of macrocyclic lactones against parasites?

• A. They activate glutamate-gated chloride channels in parasites causing hyperpolarization and paralysis
• B. They inhibit DNA replication in parasites
• C. They block sodium channels in parasite nerves
• D. They disrupt glycolysis in parasites

Answer: (A)

Macrocyclic lactones kill parasites by activating ligand-gated chloride channels in the parasite nervous system, especially glutamate-gated chloride channels. When these channels open, chloride ions flow into the nerve cells, causing hyperpolarization and paralysis. With impaired nerve transmission, the parasite can’t move or feed effectively, leading to death. This mechanism is specific to invertebrate receptors, which explains the selectivity for parasites over the host. Other mechanisms like inhibiting DNA replication, blocking sodium channels, or disrupting glycolysis describe different drug classes and don’t explain how macrocyclic lactones exert their antiparasitic effect.