What distinguishes macrocyclic lactones from other anthelmintics?

Macrocyclic lactones are distinguished by their specific activity against invertebrates, including various parasitic worms, while demonstrating a high safety margin for mammals. This safety profile is significant because it allows for effective treatment of infections without causing harm to the host animal, making them one of the preferred classes of anthelmintics in both veterinary and human medicine.

The mechanism of action of macrocyclic lactones involves the binding to specific glutamate-gated chloride channels, leading to paralysis and death of the parasite. Their efficacy against a broad range of nematodes and other ectoparasites while being relatively safe for mammals underlines their importance in treating parasitic infections.

In contrast, the other choices do not accurately represent the characteristics of macrocyclic lactones. They are indeed effective against nematodes, not specific to mammalian parasites, and while some may be derived from natural sources rather than purely synthetic compounds, the key feature that stands out is their high selective toxicity for invertebrates compared to mammals.