A cross-over study of oral and intravenous administration of theophylline in male volunteers. Absolute bioavailability of theophylline tablets.

Seven normal male volunteers each received an injection of 208 mg theophylline anhydride for 4 min, and a 185-mg single oral dose theophylline anhydride (Broncho-Afonilum) on separate occasions. The concentrations of unchanged theophylline was analyzed over a 24-h period in plasma and a 48-h period in urine after both dosage forms. A 2-compartment model was required to describe the intravenous plasma concentration-time course in all seven subjects. A 1-compartment model sufficed to account for the decay of the oral plasma concentrations in all subjects. The mean plasma t1/2 after i.v. dosing was 6.5 h (3.5-9 h), and the mean plasma t1/2 after oral doses was 5.7 h (3-12 h). The calculated total of 23% (11-70%) of the intravenous dose was excreted in urine, and the mean total excretion after the oral dose was 12% (7-19%). The absolute bioavailability of oral theophylline was 94 +/- 20%