The effects of atropine on pharmacokinetics of theophylline in rabbits.

: The effects of atropine on serum concentrations and pharmacokinetics of theophylline were studied in six rabbits (2.07 +/- 0.11 kg). Theophylline serum concentration was determined by ultraviolet spectrophotometry. After i.v. administration of aminophylline 12.5 mg/kg, i.m. atropine 1 mg/kg decreased significantly the maximal serum concentration of theophylline from 23.6 +/- 1.1 to 19.6 +/- 1.1 mg/l, and increased that of theophylline at the time of 6 and 8 hours after injection. After i.v. aminophylline administration without or with atropine, the pharmacokinetic parameters of theophylline calculated using a one compartment open model were: K (elimination rate constant) = 0.23 +/- 0.03, 0.19 +/- 0.02/h; t1/2 (half life) = 3.04 +/- 0.40, 3.66 +/- 0.40 h; Cl (clearance) = 0.26 +/- 0.04, 0.23 +/- 0.03 l/kg/h, respectively (P less than 0.01). But there was no significant variation in modification of volume of distribution (Vd). The results suggested that there is a significant drug interaction between atropine and theophylline.