Ivermectin levels vary in tissues and species

Ivermectin (IVM) is high in faeces, not found in urine but low in skin, saliva and breastmilk of man. Plasma levels vary according to species. Binding to plasma proteins varies also. Resistance of some farm animal nematodes to the avermectins have been reported. A small percentage of patients show poor reduction in skin mf after yearly treatment with ivermectin. We suggest that tissue bioavailability of free drug must be ascertained before interpreting animal models and chemotherapy programs