[Pharmacokinetics of oral theophylline. Comparison between asthmatic and cystic fibrosis patients].

The pharmacokinetics of oral theophylline at steady-state were comparatively investigated in 13 asthmatic patients and in 10 patients with cystic fibrosis (CF). In all patients, the drug was administered twice daily as slow-release tablets. The total daily dose of theophylline ranged from 10.8 to 29.4 mg/kg/day. For each patient, the time-course of theophylline steady-state plasma levels was studied after the morning dose. Six serial plasma samples were drawn at 0, 2, 4, 6, 8, and 12 h after dosing. Model-independent methods were used for calculating the pharmacokinetics parameters (area under the curve and clearance). The clearance values (mean +/- SD) calculated in the two patient groups were significantly different (asthmatic patients: clearance = 61.2 +/- 15.6 ml/h/kg; CF patients: clearance = 86.3 +/- 22.8 ml/h/kg; P = 0.007). It has previously been shown that the clearance of theophylline after single dose is increased in CF patients. Our study confirms this finding under steady-state conditions and demonstrates that higher theophylline doses are on the average required to treat patients with FC.