Abamectin (MK-0936) is a natural fermentation product of Streptomyces avermitilis. Ivermectin (MK-0933) is a synthetic derivative of abamectin. The chemical structure of abamectin differs from ivermectin only in the bond between carbons 22 and 23; abamectin has a double bond where ivermectin has a single bond and additional hydrogens on C-22 and C-23 (Figure 6.1). Both compounds are a mixture of homologous products with B1a and B1b components. The B1b component differs chemically from the B1a component by only 1 methylene (CH2) unit at the 26-carbon position: the ethyl group (C2H5) is a methyl group (CH3) in the B1b form. Abamectin and ivermectin are defined as containing a minimum of 80% B1a, and a maximum of 20% B1b components. Studies in our laboratories have clearly demonstrated that the individual components have very similar biological and toxicological properties and, for all practical purposes, can be considered equivalent.
KeywordsToxicity Streptomyces Cane Tritium Toxicology
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