Adrenergic Antagonists: Esmolol

ESMOLOL

Clinical Considerations

Esmolol is an ultrashort-acting selective β₁-antagonist that reduces heart rate and, to alesser extent, blood pressure. It has been successfully used to prevent tachycardia and hypertension in response to perioperative stimuli, such as intubation, surgical stimulation, and emergence. For example, esmolol (0.5–1 mg/kg) attenuates the rise in blood pressure and heart rate that usually accompanies electroconvulsive therapy, without significantly affecting seizure duration. Esmolol is as effective as propranolol in controlling the ventricular rate of patients with atrial fibrillation or flutter. Although esmolol is considered to be cardioselective, at higher doses it inhibits β₂-receptors in bronchial and vascu-lar smooth muscle.

The short duration of action of esmolol is due to rapid redistribution (distribution half-life is 2 min) and hydrolysis by red blood cell esterase (elimination half-life is 9 min). Side effects can be reversed within minutes by discontinuing its infu-sion. As with all β₁-antagonists, esmolol should be avoided in patients with sinus bradycardia, heart block greater than first degree, cardiogenic shock, or overt heart failure.

Dosing & Packaging

Esmolol is administered as a bolus (0.2–0.5 mg/kg) for short-term therapy, such as attenuating the car-diovascular response to laryngoscopy and intu-bation. Long-term treatment is typically initiated with a loading dose of 0.5 mg/kg administered over 1 min, followed by a continuous infusion of 50 mcg/kg/min to maintain therapeutic effect. If this fails to produce a sufficient response within 5 min, the loading dose may be repeated and the infusion increased by increments of 50 mcg/kg/min every 5 min to a maximum of 200 mcg/kg/min.

Esmolol is supplied as multidose vials for bolus administration containing 10 mL of drug (10 mg/mL). Ampules for continuous infusion (2.5 g in 10 mL) are also available but must be diluted prior to administration to a concentration of 10 mg/mL.