Sustained‐release theophylline pharmacokinetics in the cat

Theophylline was administered in a three‐way crossover design study to six cats intravenously (Aminophylline USP, Invenex Laboratories, Chagrin Falls, OH) and orally as two sustained‐release formulations (Slo‐bid Gyrocaps® (SB), William H. Rorer, Inc., Fort Washington, PA; Theo‐Dur® Tablets (TD), Key Pharmaceuticals, Miami, FL). Values were determined for mean residence time (SB = 19.4 ± 3.2 h; TD = 15.8 ± 4.8 h), mean absorption time (SB = 8.0 ± 2.3 h; TD = 4.8 ± 2.3 h), absolute bioavailability (SB = 82 ± 27%; TD = 76 ± 38%), and time to peak plasma concentrations (SB = 8 h; TD = 8 h). After normalization to a dose of 25 mg/kg, the average peak plasma concentrations were also predicted (SB = 10.5 ± 3.4 μg/ml; TD = 14.3 ± 6.7 μg/ml). Slo‐bid® was predicted to provide the least peak: trough fluctuation in theophylline concentrations. Slo‐bid® and Theo‐Dur® appear to have pharmacokinetic characteristics which, if given once‐daily, would maintain plasma theophylline concentrations of 5–20 μg/ml in the cat.