Esmolol

Esmolol is an ultra short acting intravenous beta 1 selective blocker. Red cell esterases break it down within minutes, so effects fade rapidly after stopping. It is used for acute control of supraventricular tachycardia, atrial fibrillation, perioperative tachycardia and hypertension, and aortic dissection.

Classification. Cardioselective beta 1 blocker; ultra short acting.

Mechanism. Competitive beta 1 blockade slows sinus rate and atrioventricular conduction and reduces contractility. Selectivity is lost at high doses.

Pharmacodynamics. Onset within 2 to 5 minutes; steady state within 5 minutes with a loading dose; effects end within 10 to 30 minutes of stopping.

Pharmacokinetics. Distribution half life 2 minutes; elimination half life about 9 minutes. Hydrolysed by red cell esterases, independent of liver or kidney function; the acid metabolite is excreted in urine.

Supraventricular tachycardia and atrial fibrillation rate control, adult.

• Loading dose 500 micrograms/kg IV over 1 minute.

• Then infusion 50 micrograms/kg/minute for 4 minutes.

• If the response is inadequate, repeat the loading dose and increase the infusion by 50 micrograms/kg/minute every 4 minutes, to a usual maximum of 200 micrograms/kg/minute (up to 300 micrograms/kg/minute in some labels).

• Once the target is reached, omit the loading dose in further steps.

• Duration: short term, usually up to 48 hours.

Intraoperative and postoperative tachycardia and hypertension, adult. Bolus 80 mg (about 1 mg/kg) over 30 seconds, then 150 micrograms/kg/minute, titrated to a maximum 300 micrograms/kg/minute. Alternatively 500 micrograms/kg over 1 minute then 50 to 300 micrograms/kg/minute.

Aortic dissection, adult. Load 500 micrograms/kg IV over 1 minute, then 50 to 200 micrograms/kg/minute to reach heart rate under 60/min and systolic pressure 100 to 120 mmHg; add a vasodilator if pressure stays high. Give the beta blocker before the vasodilator.

Thyroid storm and other uses (specialist). Loading 250 to 500 micrograms/kg then 50 to 100 micrograms/kg/minute titrated to heart rate.

Children. Loading 500 micrograms/kg over 1 minute, then 50 to 200 micrograms/kg/minute; specialist.

Contraindications. Severe sinus bradycardia; heart block greater than first degree; sick sinus syndrome; cardiogenic shock; decompensated heart failure; pulmonary hypertension; hypersensitivity; concomitant IV verapamil or diltiazem given near it.

Warnings. Hypotension is common and dose related. Local reactions, phlebitis and tissue necrosis with extravasation, especially from the concentrated 100 mg/mL ampoule. Bronchospasm in reactive airway disease. Masks hypoglycaemia. Raises potassium slightly.

Adverse effects. Hypotension, bradycardia, injection site reaction, nausea, dizziness, sweating, confusion.

Interactions. Verapamil and diltiazem: severe bradycardia, asystole. Digoxin: raised digoxin levels. Morphine raises esmolol levels slightly. Suxamethonium: prolonged block. Calcium channel blockers and other negative inotropes add effects.

Special groups.

• Pregnancy: avoid prolonged use; risk of foetal bradycardia.

• Breastfeeding: no data; the short half life limits exposure.

• Older adults: start low and titrate slowly.

• Kidney impairment: no adjustment of the active drug; the metabolite accumulates in severe failure.

• Liver impairment: no adjustment.

Formulations. Premixed bags 10 mg/mL (2500 mg in 250 mL; 100 mg in 10 mL vial); concentrate ampoules 250 mg/mL must be diluted.

Preparation. Use the 10 mg/mL premixed solution. Do not use the concentrated ampoule undiluted. Infuse through a large vein by pump. Do not mix with sodium bicarbonate. Compatible with 0.9% sodium chloride and 5% glucose.

Baseline. Heart rate, rhythm, blood pressure, ECG.

Monitoring. Continuous ECG and blood pressure; infusion site; reduce or stop for systolic pressure under 90 mmHg or heart rate under 50/min.

Stopping. Stop the infusion; effect fades within 30 minutes. For long term control, begin oral therapy as the infusion is reduced.

Common prescribing errors. Confusing the 250 mg/mL concentrate with the 10 mg/mL premixed solution; giving it with IV verapamil; confusing micrograms/kg/minute with mg/kg.