Pharmacokinetics of theophylline and enprofylline in patients requiring a high or low dose of theophylline.

In patients requiring a high or low dose of theophylline the pharmacokinetics of theophylline and enprofylline were studied. The low-dose group took an average daily dose of 8.91 mg/kg body wt. and the high-dose group 24.75 mg/kg body wt. The average half-life of theophylline in the former was 7.11 h and in the latter 4.72 h. The average clearances (CL) of theophylline were 2.83 and 4.58 l/h, respectively. The daily oral intake of theophylline was negatively correlated with the theophylline t1/2 (r = -0.63). While the t1/2 of enprofylline was similar in the two groups, CL and volume of distribution (Vc) were slightly (about 30%) but significantly higher in patients requiring a high dose of theophylline. CL of enprofylline did not correlate with CL of theophylline, nor was the Vc of the two drugs correlated. Interindividual variability in t1/2 and CL was considerably lower for enprofylline than for theophylline.