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 single dose administration of uncoated tablets (Oxyphyllin) was completed within 2 hrs, whereas the absorption from sustained-release tablets (Theo-Dur) continued for 12 hrs. There was no significant difference in bioavailability between aminophylline i.v., Oxyphyllin tablets and Theo-Dur tablets. The slow-release tablet gave a stable plasma level in steady state that implies the possibility of using 12-hr dosage intervals and still achieving 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.