Comparative study of beta-adrenoceptor blocking efficacy of two formulations of esmolol in vivo and in vitro.

The objective of the present study was to compare the cardiovascular beta-blocking activity of two different formulations of esmolol. Spontaneously beating guinea-pig isolated atria and the heart rate and blood pressure of anaesthetized cat were employed in the study to compare the beta-blocking efficacy of the two formulations of esmolol using isoprenaline as an agonist. In guinea-pig isolated atria the standard esmolol formulation (Brevibloc) reduced basal atrial rate more significantly than the indigenously formulated esmolol (test formulation). Both the formulations produced similar parallel rightward shift of cumulative concentration response curves of isoprenaline with closely comparable pA2 values. In anaesthetized cats, only indigenous esmolol formulation significantly decreased basal heart rate. Both the formulations did not modify the basal blood pressure and isoprenaline-induced fall in blood pressure, despite significantly blocking isoprenaline-induced tachycardia. It is suggested that both the formulations produced similar degree of beta-1 adrenoceptor blocking activity.