ABSTRACT
Caffeine (1,3,7-trimethylxanthine) is one of the most widely consumed pharmacological agents throughout the world. Apart from its well-documented effects on the central nervous system, cardiovascular system, smooth muscle, gastrointestinal tract, and kidneys, there is a perception that caffeine enhances athletic performance. The studies outlined in this chapter \and elsewhere were designed to assess urine caffeine concentrations achieved during controlled and uncontrolled steady-state caffeine intake in healthy subjects. In addition, the intra- and interindividual variability in plasma and urine caffeine concentrations were determined, as were effects of urine flow rate on urine caffeine concentration. Caffeine renal clearance was calculated as the caffeine excretion rate divided by the midpoint plasma caffeine concentration. Plasma and urine concentrations of caffeine have been determined at steady state in two groups of healthy subjects. Some individuals may consequently be at risk of exceeding the current international urine caffeine concentration limit of 12 mg/L following modest intake of caffeine-containing foods and drinks.
