Effect of dose size on the pharmacokinetics of orally administered quinine

Plasma concentrations of quinine were measured by high-performance liquid chromatography (HPLC) after oral administration of 250, 500 and 1000 mg base to seven healthy adults. The doses were administered after an overnight fast. A washout period of at least 21 days was allowed between the doses. Area under the plasma concentration-time curve (AUC) for quinine increased in approximate proportion to the dose from 250 to 1000 mg. There was also a linear relationship between dose and maximum plasma concentration and dose and AUC in individual subjects. Time to reach peak plasma concentration remained unchanged over the dose range. There was no significant difference in elimination half-life, volume of distribution and systemic clearance over the dose range. The occurrence of adverse effects was dose and plasma quinine concentration dependent; central nervous system side effects increased as dose and plasma concentrations increased. These data suggest that after oral administration of quinine, linear pharmacokinetics occur in the dose range of 250-1000 mg.