Clinical Pharmacokinetics and Therapeutic Efficacy of Esmolol

Esmolol is a unique cardioselective β₁-receptor blocking agent with a rapid onset and short duration of action. Since our previous review in 1995, the pharmacokinetics and efficacy of esmolol have been investigated in a number of acute care settings. Three studies investigated the pharmacokinetics and safety of esmolol in the paediatric population. The disposition of esmolol in children was found to be linear with plasma concentrations increasing in proportion to dose over the ranges studied. The pharmacokinetic estimates for esmolol showed a shorter elimination half-life (t_1/2) [2.7–4.8 minutes] and a higher clearance (281 mL/kg/min) in newborns and infants than that found in children (>2 years old) and adults. Dosing requirements to achieve targeted blood pressure in post-coarctectomy patients were substantially higher (mean 700 μg/kg/min) than that used in adults. Esmolol was effective in controlling hypertension following cardiac surgery and terminating supraventricular arrhythmias in children.

The efficacy of esmolol has been established in a variety of patients, including those with unstable angina, myocardial ischaemia, supraventricular arrhythmias, peri- and postoperative tachycardia and hypertension, and electroconvulsive therapy. With careful titration and monitoring, esmolol can be used effectively in patients with congestive heart failure and chronic obstructive lung disease because of its unique short t_1/2 and β₁-selectivity. Different dosage schedules have been developed depending on clinical setting and diagnosis. Generally, a loading dose of ≤500 μg/kg/min over 1 minute is administered followed by a continuous infusion of 25–300 μg/kg/min. Hypotension, being the primary adverse effect, can be minimized by careful dosage titration and patient monitoring.

In the perioperative setting involving tracheal intubation and extubation, a number of recent studies have suggested that titration of esmolol to a haemodynamic endpoint can be safe and effective, resulting in a decreased incidence of myocardial ischaemia. The most effective regimen in attenuating the response to heart rate and blood pressure after laryngeal tracheal intubation was a loading dose of 500 μg/kg/min for 4 minutes followed by a continuous infusion of 200–300 μg/kg/min. In cardiac and non-cardiac surgical patients esmolol has been shown to decrease episodes of myocardial ischaemia and arrhythmias. In the perioperative period for non-cardiac surgery routine use of β-blockers (β-adrenoceptor antagonists) is no longer recommended. However, in patients at high risk for myocardial ischaemia or undergoing high-risk surgery where a β-blocker is indicated, esmolol is the ideal perioperative agent to minimize the risk of hypotension and bradycardia based on its pharmacodynamic and pharmacokinetic characteristics. For postoperative patients in atrial fibrillation, esmolol achieves rapid ventricular rate control. However, for the prevention of postoperative atrial fibrillation esmolol provides no advantage over oral β-blockers. In other situations where emergent β-blockade is required, such as electroconvulsive therapy, esmolol has been shown to effectively control haemodynamic response. After more than 2 decades of use esmolol continues to provide an important therapeutic option in the acute care setting.