Evaluation of slow-release theophylline pharmacokinetics by Fourier's harmonic analysis

Theophylline absorption from two sustained-release theophylline formulations was examined over 2 consecutive days during continuous therapy in 7 asthma patients. We compared two twice daily formulations of Teotard capsules (TC) and Teolin tablets (TT). Bioavailability for each 12-h period was defined as: BIO = (AUC oral/AUC iv) x (Dose iv/Dose oral)x100. The amount of theophylline absorbed during each 2-h interval was calculated using modified Wagner-Nelson equation for multiple dose drug administration. Mean serum theophylline concentrations were analysed by Fourier's harmonic analysis (FHA) and by F test. There were not statistically significant differences between TT and TC neither for BIO nor for fractional absorption calculated for 2-h sampling intervals. On the other hand FHA of mean SCT disclose more predictable theophylline absorption from TT compared to TC. We conclude that in order to obtain complete pharmacokinetic profile of slow-release formulation FHA should also be included into the calculations.