The pharmacokinetics of primaquine in calves after subcutaneous and intravenous administration

The pharmacokinetics of primaquine was studied in calves of 180–300 kg live weight. Primaquine was injected at 0.29 mg/kg (0.51 mg/kg as primaquine diphosphate) intravenously (IV) or subcutaneously (SC) and the plasma concentrations of primaquine and its metabolite carboxyprimaquine were determined by high-performance liquid chromatography. The extrapolated concentration of primaquine at zero time after IV administration was 0.50±0.48 µg/ml (mean ±SD) which decreased with an elimination half-life of 0.16±0.07 h. Primaquine was rapidly converted to carboxyprimaquine after either route of administration. The peak concentration of carboxyprimaquine was 0.50±0.08 µg/ml at 1.67±0.15 h after IV administration. The corresponding value was 0.47±0.07 µg/ml at 5.05±1.20 h after SC administration. The elimination half-lives of carboxyprimaquine after IV and SC administration were 15.06±0.99 and 12.26±3.06 h, respectively. The areas under the concentration-time curve for carboxyprimaquine were similar following either IV or SC administration of primaquine; the values were 11.85±2.62 µg.h/ml after the former and 10.95±2.65 µg.h/ml after the latter. The mean area under the concentration-time curve for primaquine was less than 0.1 µg.h/ml after either route of administration.