Effect of antacid on bioavailability of theophylline from rapid and timed-release drug products.

Magnesium aluminum hydroxide suspension (an antacid) was given concurrently with either theophylline anhydrous tablets or theophylline anhydrous timed-release capsules to 13 volunteers using a four-way crossover design. Serum theophylline was measured by reversed-phase high-pressure liquid chromatography. The serum level-time curves were individually fitted to an oral absorption one-compartment open model. The pharmacokinetic parameters (mean +/- SD) KA, K, AUC, and F/V for theophylline from the rapid release theophylline anhydrous tablets were 2.1 +/- 1.3 hr-1, 0.15 +/- 0.06 hr-1, 89.2 +/0 39 microgram hr/ml, and 0.0023 +/- 0.002 kg/ml, respectively; from the anhydrous timed-release capsules, they were 0.27 +/- 0.08 hr-1, 0.20 +/- 0.07 hr-1, 79.0 +/- 27 microgram hr/ml, and 0.0030 +/- 0.007 kg/ml, respectively. The concurrent administration of 15 ml of antacid (magnesium aluminum hydroxide suspension) with the theophylline products did not significantly affect any of these pharmacokinetic parameters. The extent of theophylline bioavailability from all drug products was consistent and similar as shown by the F/V and AUC values.