Dissolution studies of some sustained-release theophylline dosage forms.

Dissolution studies were carried out with the USP rotating-basket apparatus in both simulated gastric and intestinal fluids. Four different brands of sustained-release theophylline products of different strengths (nine formulations) were studied. The percentage of the dose released in 1 h in gastric fluid ranged from (mean +/- SD) 6.6 +/- 0.9 to 50.1 +/- 3.8%. By 6 h, the percentage of the dose released ranged from 10.8 +/- 1.8 to 86.5 +/- 5.2%. Similar formulations of different strengths released significantly different fractions of their dose at respective sampling times. In intestinal fluid, some formulations released 100% of their dose within 3-4 h, behaving more like enteric-coated preparations. One dosage form appeared to release drug by an apparent zero-order rate. From one brand of theophylline (two strengths), only 48.1 +/- 5.6 and 29.9 +/- 4.1% of label strength, respectively, dissolved in 25 h in intestinal fluid. Some of these in vitro results were rank-correlated to previously reported bioavailability and pharmacokinetic studies.