Pharmacokinetic and Clinical Studies with Caffeine

Abstract

A preliminary study was carried out to investigate the pharmacokinetics of caffeine. Four healthy adult volunteers each received 200mg, 400mg and 600mg doses of caffeine on separate mornings, having abstained from food and drink containing methylxanthines for the previous 24 hours. Blood, saliva and urine samples were taken at intervals during the next 24 hours. Determinations of caffeine, paraxanthine, theobromine and theophylline concentrations in the samples were made by high performance liquid chromatography. Caffeine concentrations in plasma and saliva decreased in a log-linear relationship with time, indicative of first-order kinetics, however this relationship did not hold for the metabolites. Mean ± standard deviation plasma caffeine clearance was 1.10 + 0.45ml/min/kg and mean half-life was 7.1 ± 3.2 hours. Saliva/plasma caffeine concentration ratios showed time dependence with high values initially. Only 2.8 ± 0.5% of the caffeine dose was excreted unchanged in urine...