Computer-simulated conversion from intravenous to sustained-release oral theophylline

A computer equipped with a pharmacokinetic program was used to theoretically determine the proper time to administer the first dose of a commonly prescribed, sustained-release oral theophylline product (Theo-Dur) in patients maintained on a continuous intravenous aminophylline infusion. Four conversion methods were tested. They included giving the first oral dose (1) immediately upon discontinuation of the iv infusion, (2) two hours after discontinuing the iv infusion, (3) four hours after discontinuing the iv infusion, and (4) two hours before discontinuing the iv infusion. Each of the four methods was simulated in three groups of patients: smokers, nonsmokers, and patients with cirrhosis. Results showed that, in most situations, given the first oral dose immediately upon discontinuation of the intravenous infusion provided minimal deviation from eventual steady-state levels. In addition, this computer simulation suggests that the initial 12-hour maintenance dose recommended by the FDA may result in toxicity in certain patient groups.