ABSTRACT
The macrocyclic lactone class of antibiotics has been a significant addition to human and veterinary medicine since their discovery some 30 years ago. They exhibit a broad spectrum of activity against a range of nematodes and arthropods, are active at low concentration, and have a wide margin of safety. They are classified into two major subfamilies—the avermectins and milbemycins. The differences are based on the presence or the absence of a sugar motif and protonation at C-13. Although the avermectins were the first to be commercialized, the milbemycins were discovered earlier, with milbemycin first identified in 1972 (Takiguchi et al., 1980). This chapter focuses on ivermectin and moxidectin—the two macrocyclic lactones of greatest relevance to human clinical use.
