Theophylline disposition in obesity

Theopylline disposition was examined in 14 obese subjects and 57 normal subjects. A single oral dose of aminophylline solution was given and serum and saliva samples were collected over several hours and assayed by high-pressure liquid chromatography. The apparent volume of distribution (V_d) and body clearance (Cl_B) were analyzed for total body weight (TBW) and ideal body weight (IBW). The V_d averaged 0.482 (SD = 0.084) L/kg TBW in normals vs 0.382 (0.069) L/kg TBW and 0.77 (0.189) L/kg IVW in obese subjects. The Cl_B averaged 63.0 (28.5) ml/hr/kg IBW in normal compared to 32.8 (11.1) ml/hr/kg TBW and 64.1 (20.8) ml/hr/kg IBW in obese subjects. Similar V_d values between thw two groups when TBW is used indicates that loading dose is best calculated based on TBW. Similar Cl_B based on IBW in normal and obese subjects indicates that IBW should be used to calculateaintenance doses for theophylline. Mean half-lives were longer in obese subjects than in normal, 8.6 (2.0) and 6.0 (2.1) h, respectively, suggesting that obese patients may need less frequent dosing.