Wiktionary
milbemycin
n. Any of various products of fermentation by ''Streptomyces'' bacteria, sometimes used in medicine.
Wikipedia
Milbemycin
The milbemycins are a group of macrolides chemically related to the avermectins and were first isolated in 1972 from Streptomyces hygroscopicus. They are used in veterinary medicine as antiparasitic agents against worms, ticks and fleas.