Esmolol acid is an active metabolite of the β1-adrenergic receptor (β1-AR) antagonist esmolol .1 It is formed from esmolol via hydrolysis by a red blood cell esterase. Esmolol acid inhibits isoproterenol-induced increases in the beating rate of isolated guinea pig right atria (pA2 = 3.73) and prevents tachycardia and hypotension induced by isoproterenol in anesthetized dogs in a dose-dependent manner.2 It is also a potential impurity in commercial preparations of esmolol.3
1.Jahn, P., Eckrich, B., Schneidrowski, B., et al.β1-adrenoceptor subtype selective antagonism of esmolol and its major metabolite in vitro and in man. Investigations using tricresylphosphate as red blood cell carboxylesterase inhibitorArzneimittelforschung45(5)536-541(1995) 2.Shaffer, J.E., Quon, C.Y., and Gorczynski, R.J.β-adrenoreceptor antagonist potency and pharmacodynamics of ASL-8123, the primary acid metabolite of esmololJ. Cardiovasc. Pharmacol.11(2)187-192(1988) 3.Sahadev Reddy, M., Reddy, M.S.N., Rajan, S.T., et al.Structural identification and characterization of impurities in esmolol hydrochlorideDer Pharma Chem.8(4)296-300(2016)