Influence of formulation on bioavailability of theophylline.

The bioavailability of theophylline from formulations containing this drug alone and also in combination with phenobarbital and ephedrine has been studied in normal volunteers and asthmatic subjects. Neither of the latter two drugs had any significant influence on the bioavailability of theophylline. A complexation phenomenon, previously reported to inhibit dissolution of theophylline and phenobarbital in vitro, does not affect the bioavailability of theophylline from solid formulations. No differences were observed in the pharmacokinetics of theophylline between normal and asthmatic subjects.