Abstract:Simultaneous administration of terbutaline and theophylline to guinea pigs did not cause significant alterations of the pharmacokinetic properties of any of the drugs. Terbutaline sulphate 24 μg kg−1and aminophylline 52 mg kg−1(7.42.10−8and 2.37.10−4mol kg−1respectively) were given by a bolus intravenous injection, producing plasma concentrations in the range 0–15 ng terbutaline sulphate per ml (0–46 nanomol 1−1) and 10–85μg theophylline per ml (50–429 μmol 1−1). Pharmacokinetic analyses of time courses of plasma concentrations of intact drugs and investigations of tissue distribution 1 hour after the administration were performed. The results showed a weak, statistically insignificant trend of the peripheral compartment of the 2‐compartment model to sequester a larger fraction of the drugs when these were a