Methods of comparing pharmacokinetics of slow release preparations: a comparison of "Theo-Dur" and "Phyllocontin" in patients with asthma.

The pharmacokinetics of two slow release theophylline preparations "Theo-Dur" (T) containing theophylline only and "Phyllocontin" (P) containing aminophylline have been compared in 12 patients with asthma. Each patient received both treatments in random order. The dose of treatment administered 12 hourly was increased or decreased to produce plasma theophylline concentrations of 10-20 mg/l at clinic visits normally 7 to 8 h after dosing. Pharmacokinetic studies were carried out after at least one week's treatment with this dose. After the first study day patients were crossed over to the second treatment at a dosage providing a similar amount of theophylline. They returned for a second study day after at least one week. Comparison of the dose corrected AUC, time to peak concentrations, within patient coefficients of variation (CV), number of concentration time points falling within 25% of Cmax and percentage fluctuations in plasma concentration showed no significant differences between the two preparations.