Theophylline controlled-release formulations: in vivo-in vitro correlations

Four experimental controlled-release oral solid dosage formulations were developed and the in vitro dissolution characteristics of theophylline from these formulations were studied in USP apparatus I. Pharmacokinetic evaluation of these formulations was carried out in eight beagle dogs under fasting conditions. Theophylline in a 5% dextrose injection USP, oral solution, and Slo-Phyllin were used as controls to estimate the in vivo dissolution of these four formulations in the GI tract. The percentage cumulative amounts of drug absorbed and the percentage cumulative amounts of drug released into the GI tract from these four controlled-release formulations were obtained by numerical deconvolution methods. The in vivo and in vitro dissolution data demonstrated good correlation indicating that in vitro dissolution tests can be used to optimize the further design of controlled drug release oral solid dosage formulations for theophylline.