Theophylline kinetics: dose dependency and single sample prediction of clearance.

Theophylline clearance was measured at 3 doses (2, 4 and 6 mg/kg) in 10 young, healthy adult subjects. Clearance decreased as the dose of theophylline increased going from 0.064 +/- 0.016 to 0.052 +/- 0.011 1.h-1.kg-1 at the 2 and 6 mg/kg doses, respectively (p less than 0.02). A simplified method for estimating theophylline clearance was tested using single plasma concentrations of theophylline and assuming a constant value (0.5 l/kg) for volume distribution of theophylline. This method gave the best results when samples were drawn at 12 or 24 h after a 2 or 4 mg/kg intravenous dose of theophylline, respectively, and was effectively applied in estimating the quantitative impact of cimetidine administration on theophylline clearance.