title: Breed differences on the plasma availability of moxidectin administered pour-on to calves.
abstract: The pharmacokinetic profile of avermectin and milbemycin compounds is affected by different drug- and host-related factors. This work reports the influence of cattle breeds on the plasma kinetics of moxidectin (MXD) after topical (pour-on) administration. Parasite-free Aberdeen Angus and Holstein calves were treated with a commercial MXD pour-on formulation at 500 microg/kg. Blood samples were collected over a period of 35 days post-treatment and the recovered plasma was analysed by high performance liquid chromatography using fluorescence detection. MXD was detected in plasma from two hours up to 35 days post-treatment in animals from both breeds. A slow MXD absorption and delayed peak plasma concentration were observed in Aberdeen Angus compared to Holstein calves. Significant lower systemic availability (expressed as AUC) (P<0.01) and peak plasma concentration (C(max)) (P<0.05) were also observed in Aberdeen Angus calves, although the plasma mean residence time (MRT) and elimination half-lives (T(1/2el)) of MXD in both breeds were similar. The pharmacokinetic differences observed between cattle breeds contribute to explain the variability in the pattern of clinical efficacy for pour-on administered endectocide compounds reported in different field trials.
mesh_terms: D000287:Administration, Topical; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D002417:Cattle / Q000097:blood / Q000378:metabolism*; D006207:Half-Life; D007306:Insecticides / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D016014:Linear Models; D018942:Macrolides; D008297:Male
chemical_list: D000900:Anti-Bacterial Agents; D007306:Insecticides; D018942:Macrolides; C027837:moxidectin