Comparison of the in vitro dissolution properties and in vivo steady-state pharmacokinetics of two sustained-release theophylline preparations

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Abstract
The sustained-release properties and relative bioavailability of Theolin® Retard and Pharphylline® Retard were studied in eight healthy adults after treatment for five days with twice daily 450 mg, respectively 425 mg. During the day-time dosing interval on the fourth and fifth day theophylline plasma concentrations were assayed by HPLC. After intake of Theolin® Retard, minimum theophylline plasma concentrations were significantly higher, fluctuations in theophylline plasma concentrations were significantly smaller andt 75 (the period within a dosing interval during which the plasma concentration exceeds 75% of the maximal concentration) was significantly longer than after Pharphylline® Retard. Maximal concentrations and AUC values were not significantly different. For both products the plasma concentration time-curves on day 5 were significantly lower than on day 4.In vitro dissolution tests confirmed the more sustained release of theophylline from Theolin® Retard. These results indicate an equal extent of absorption from the two products but better sustained-release properties for Theolin® Retard.