Depletion of moxidectin tissue residues in sheep

The pattern of tissue depletion of moxidectin (MXD) subcutaneously administ ered to sheep was characterized in this study. MXD concentration profiles w ere determined in muscle, fat, and liver and at the site of injection follo wing administration of a formulation combining MXD (0.5% w/v) with a standa rd 6 in 1 clostridial vaccine. Thirty-five (35) parasite-free Lincoln sheep were treated with the MXD injectable formulation at a dose rate of 0.2 mg of MXD/kg of live weight, administered subcutaneously on the inner surface of the thigh. Treated animals were sacrificed in randomly selected groups o f six sheep weekly from day 21 until day 49 post-treatment. Three nontreate d animals were sacrificed to obtain blank. tissue samples to validate the a nalytical methodology. MXD concentration profiles were determined by a vali dated HPLC analytical method using fluorescence detection. MXD has an adequ ate pattern of absorption, based on the low residual concentrations found i n the injection site area at all sampling intervals. Muscle samples showed the lowest MXD concentrations throughout the study period. The highest MXD concentrations at all sampling times were measured in the adipose tissue, i ndicating that fat is a target tissue for MXD. MXD concentrations in all of the tissues analyzed were below the accepted maximum limit of residue at 2 1 days post-treatment.