The pharmacokinetics of moxidectin following intravenous and topical administration to swine

The pharmacokinetic parameters of moxidectin (MXD) after intravenous and pour-on (topical) administration were studied in sixteen pigs at a single dose of 1.25 and 2.5 mg/kg BW (body weight), respectively. Blood samples were collected at pretreatment time (0 hr) over 40 days. The plasma kinetics were analyzed by WinNonlin 6.3 software through a noncompartmental model. For intravenous administration (n = 8), the elimination half-life (lambda(Z)), the apparent volume of distribution (V-z), and clearance (Cl) were 10.29 +/- 1.90 days, 89.575 +/- 29.856 L/kg, and 5.699 +/- 2.374 L/kg, respectively. For pour-on administration (n = 8), the maximum plasma drug concentration (C-max), time to maximum plasma concentration (T-max), and lambda(Z) were 7.49 ng/ml, 1.72, and 6.20 days, respectively. MXD had a considerably low absolute pour-on bioavailability of 9.2%, but the mean residence time (MRT) for pour-on administration 10.88 +/- 1.75 days was longer than 8.99 +/- 2.48 days for intravenous administration. These results showed that MXD was absorbed via skin rapidly and eliminated slowly. The obtained data might contribute to refine the dosage regime for topical MXD administration.