[The effect of bile secretion on the pharmacokinetics of a theophylline sustained-release preparation]

Bile excretion changes the physiological milieu of the duodenum, possibly resulting in enhanced absorption of a drug due to increased solubilisation. This possible influence of bile salts following stimulation of gallbladder emptying by the release of cholecystokinin on the pharmacokinetics of a sustained release theophylline (CAS 58-55-9) preparation (Bronchoretard) was evaluated in this study. An open, randomised, 3-way crossover study in 12 healthy, non-smoking volunteers was selected to prove or reject this hypothesis. All subjects received 500 mg of the sustained release theophylline formulation under two different cholagogia stimulating test conditions compared with a fasting reference condition. A standard breakfast and i.m. administration of cholecystokinin enabled a reproducible modulation of bile flow: a moderate and extreme contraction of the gallbladder could be induced after a standard breakfast and after i.m. administration of cholecystokinin, respectively. Following a standard breakfast, gallbladder volumes were approximately halved (50.6%) compared to the baseline volume after 79 min. Injection of 0.3 microgram/kg body weight cholecystokinin resulted in fast and complete gallbladder evacuation (94.6%) 36 min after the application of this cholagogue stimulus. Gallbladder volumes remained more or less constant under fasting conditions. This manipulation of bile flow did not influence concentration/time profiles of the sustained release theophylline preparation compared to the fasting condition. Even almost complete evacuation of the gallbladder after administration of cholecystokinin did not modify the concentration/time profile of theophylline in a relevant way. An unintentional rapid release of theophylline could be excluded for this sustained release formulation for all three treatments, as not a single case of dose dumping was observed. Furthermore, in vitro dissolution investigations using synthetic surfactants can predict neither food effects nor bile influence on the in vivo absorption at least for the sustained release formulation tested.