Investigations on caffeine passage into the canine gastric juice

Two caffeine boluses (5 and 10 mg/kg) were i.v. administered to four gastric fistula dogs. Gastric secretion was collected before and during pentagastrin stimulation (1, 2 and 4 micrograms/kg/h). Caffeine concentration in serum and gastric juice was determined by HPLC. Mean serum caffeine concentrations were clearly dose-dependent: 4.88 +/- 0.73 (n = 72) and 10.18 +/- 0.98 mg/l (n = 70). After each bolus, the time course of serum concentration was described by a single exponential, yielding an estimation of caffeine half-life: 310 +/- 46 (n = 9) and 453 +/- 59 min (n = 9), respectively. In both cases the same apparent volume of distribution: 0.87 +/- 0.02 l/kg (n = 9) was found. In gastric juice, caffeine concentration depended on the caffeine dose: 2.51 +/- 2.15 (n = 66) and 6.04 +/- 2.57 mg/l (n = 62); outputs were found to be linearly related to juice output, the slope being controlled by the caffeine dose. It was concluded that caffeine passage into gastric juice was governed by a solvent drag mechanism.