Pharmacokinetics of terbutaline and theophylline in guinea pigs when administered simultaneously.

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 microgram kg-1 and aminophylline 52 mg kg-1 (7.42 . 10(-8) and 2.37 . 10(-4) mol kg-1 respectively) 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 10-85 microgram theophylline per ml (50-429 mumol 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 administered simultaneously.