Esmolol Pharmacology — FRCA Primary MCQ
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Correct answer: B — It is relatively beta-1 selective, is hydrolysed predominantly by red-blood-cell esterases, and has a parent-drug elimination half-life of approximately 9 minutes
Explanation lettering: E = shown as A · A = shown as B · B = shown as C · C = shown as E
A is correct. Esmolol is an intravenous, relatively beta-1-selective antagonist whose ester group is rapidly hydrolysed by esterases associated with red blood cells, producing methanol and an acid metabolite. This high-capacity metabolism gives the parent drug an elimination half-life of approximately 9 minutes and permits rapid titration. Its beta-1 selectivity is relative rather than absolute, so beta-2 blockade can occur as the dose rises; it is not non-selective at usual therapeutic doses. Plasma cholinesterase is not the principal enzyme, excluding B. In D, the 9-minute half-life is incorrectly assigned to the metabolite: the acid metabolite has a half-life of about 3.7 hours and less than 0.1% of esmolol's beta-blocking activity. Hepatic CYP metabolism and prolonged parent-drug action are incorrect.
Reference: AOP Orphan Ltd. Esmolol hydrochloride 10 mg/ml solution for injection, Summary of Product Characteristics, sections 5.1–5.2; updated 5 January 2021. https://www.medicines.org.uk/emc/product/3057/smpc