Pharmacology and pharmacokinetics of esmolol

Esmolol is an ultra-short-acting beta-adrenergic blocking agent that possesses minimal partial agonist activity or direct membrane depressant activity. The short duration of action of esmolol is attributable to rapid enzymatic hydrolysis by red blood cell esterases, forming ASL-8123 and methanol. Experiments in the constant-flow-perfused isolated canine hindlimb indicate that therapeutic (beta blocking) doses of esmolol lack direct vascular effects and alpha-adrenergic blocking activity and that therapeutic doses do not interfere with vascoconstrictor effects of peripheral sympathetic nerve stimulation. Esmolol produces cardiac electrophysiologic and hemodynamic effects consistent with those of beta blockade. Specifically, esmolol decreases heart rate, depresses atrioventricular nodal conduction, and decreases determinants of myocardial oxygen demand. The beneficial antiarrhythmic and infarct-size limiting effects of esmolol have been demonstrated in several experimental models. Whereas beta blockers in general are effective in settings of supraventricular arrhythmias, sinus tachycardia, and myocardial ischemia, esmolol provides the added dimension of "titratability." Thus, the short duration of action of esmolol allows for very rapid titration to a preferred steady-state level of beta blockade; rapid adjustment to different steady-state levels of beta blockade, as may be required by changing status of the patient, and rapid disappearance of beta blockade following discontinuation of esmolol infusion, should this be necessary in the event of deleterious cardiac hemodynamic effects. Thus, esmolol is ideally suited for use in the treatment of patients in whom beta blockade is desirable, but in whom level of beta blockade must be very carefully modulated.