Ivermectin, and a lot of other drugs in the class of macrocyclic lactones, are considered "endectocides" in that they kill nematodes (endoparasites) and insects

Ivermectin, and a lot of other drugs in the class of macrocyclic lactones, are considered "endectocides" in that they kill nematodes (endoparasites) and insects (ectoparasites). I don't understand why they aren't studying moxidectin, a related compound which persists in the body at effective concentrations for a month or more.