Duration of action and plasma levels of beta-adrenoceptor blocking drugs.

Since beta-adrenoceptor blocking drugs exhibit a long duration of action "despite" an elimination half-life of usually between 2 and 6 hours, it has been postulated that no direct correlation could exist between the time course of plasma levels and that of pharmacodynamic effects. Results of a study are reported in which 20 mg pindolol were administered orally to 8 healthy volunteers. Exercise tests were carried out and pindolol levels determined at various times for up to 24 hours after drug administration. A linear fall of the pharmacological effect (reduction of exercise-induced tachycardia) and an exponential fall of pindolol plasma levels were observed, indicating a linear relationship between the reduction of exercise-induced tachycardia and the logarithm of plasma concentration.