Avermectin activity against helminths

Ivermectin is the catalytic reduction product of avermectin, a macroHde containing a spiroketal ring system. Two other related antibiotics having significantly different stmctural features and biological properties, moxidectin and milbemycin oxime, were more recentiy introduced into the market. Although these compounds have no antimicrobial activity, they are sometimes referred to as antibiotics because they are derived from fermentation products and have very selective toxicities. They have potent activity against worms or helminths and certain ectoparasites such as mites and ticks. 

Tests using helminth infections in a variety of laboratory animals soon revealed that the avermectins had activity against a variety of nematodes but lacked activity toward cestodes and trema-todes. During the course of testing in a number of other assays, they were found active against the flour beetle, Tribolium confusum (14). This activity against arthropods was confirmed in mice infected with larvae of the bot fly, Cuterebra fontinella. 

Table III. Activity of Avermectin Derivatives against Adult Gastrointestinal Helminths of Experimentally Infected Sheep on Oral Administration.

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