Disposition of 3H-selamectin and 3H-ivermectin in the brain of the cat flea Ctenocephalides felis felis using micro-image analysis

Drug disposition was visualised in cryostat sections of fleas using a micro-image analysis (MIA). A relationship between the concentration of radioactivity in the ganglia and the dose of drug in the blood meal was obtained. The concentration of selamectin in the ganglia was significantly higher than ivermectin at all doses investigated. The enhanced concentration of selamectin, at a site rich in glutamate-gated chloride channels may, in part, explain the higher potency of selamectin against fleas compared to ivermectin.