Absorption of theophylline from conventional and sustained-release tablets

Healthy adults were treated in periods of 4 days with fast dissolving theophylline tablets (Oxyphyllin, Draco, Sweden) and sustained-release tablets (Theo-Dur, Draco, Sweden). To some of the volunteers, a single dose of i.v. aminophyllamine was administered. The absorption of theophylline, calculated from a single dose administration, of uncoated tablets (Oxyphyllin) was completed within 2 hours, whereas the absorption of sustained-release tablets (Theo-Dur) continued during 12 hours. There was no significant difference in bioavailability between aminophylline i.v., Oxyphyllin tablets and Theo-Dur tablets. The slow release tablets gave a stable plasma level in steady state that implies the possibility of using 12-hour dosage intervals and still achieve a stable theophylline concentration in steady state with a small difference between peak and trough concentrations. This investigation shows that it is possible to simulate the plasma concentration of theophylline in steady state by means of oral administration, using the simple one-compartment model calculated from data registered after a single i.v. dose.