Bioavailability of four slow‐release theophylline formulations in the Beagle dog

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Abstract
Theophylline was administered to six Beagles intravenously (Aminophyllin Injectable ®, Searle Laboratories) and orally as four sustained‐release formulations (Choledyl ®‐SA Tablets, Parke‐Davis; Theo‐Dur® Tablets, Key Pharmaceuticals; Theo‐24® Capsules, Searle Laboratories, and Slo‐bid Gyrocaps®, William H. Rorer, Inc.). Values were determined for mean residence time, mean absorption time, absolute bioavailability, time to peak plasma concentration, and peak plasma concentration normalized to a theophylline dose of 20 mg/kg. In this order the values found for each formulation were: Choledyl (10.2 ± 1.8 h, 2.8 ± 2.2 h, 63 ± 10%, 3.9 ± 1.0 h, 10 ± 1.1 μg/ml), Theo‐Dur (12.1 ± 5.2 h, 4.9 ± 5.3 h, 76 ± 18% 4.7 ± 3.1 h, 12 ± 3.7 μg/ml), Theo‐24 (15.6 ± 8.9 h, 8.1 ± 8.4 h, 30 ± 16%, 3.6 ± 1.7 h, 3.5 ± 1.3 μg/ml), and Slo‐bid (11.9 ± 1.9 h, 4.4 ± 1.3 h, 60 ± 9%, 4 ± 1.1 h, 8.6 ± 0.8 μg/ml). Choledyl, Theo‐Dur and Slo‐bid appear to have absorption characteristics which, if given twice daily, would maintain therapeutic plasma concentrations of theophylline between 10 and 20 M‐g/ml in the dog. Of these, Theo‐Dur was predicted to provide the least peak:trough fluctuation in theophylline plasma concentrations.

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