A mixture consisting of >= 90% 22,23-dihydroavermectin B1a (R = Me) and <= 10% 22,23-dihydroavermectin B1b (R = H). A semi-synthetic derivative of abamectin, it is used as a broad-spectrum antiparasite medication, particularly against worms (except tapeworms), although it is also effective against most mites and some lice.