Published online by Cambridge University Press: 15 December 2009
Calcium sensitisers are a new class of positive inotropic drugs that are potentially useful in the treatment of acute decompensated heart failure. They have a unique mechanism of action that differs from other available intravenous agents such as dobutamine, a β-agonist, and milrinone, a phosphodiesterase inhibitor. Unlike dobutamine and milrinone, calcium sensitisers increase myocardial contractility without increasing cytosolic calcium release, reducing myocardial energy demand and the incidence of serious arrhythmias. Clinical trials have focused on demonstrating improved survival with levosimendan when compared to placebo and dobutamine. Levosimendan is the first intravenous calcium sensitiser to be approved in Europe for the treatment of acute decompensated heart failure.
Pharmacology
Chemical structure
Levosimendan is a pyridazinone-dinitrile derivative with the chemical name ((R) − (4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)-phenyl)hydrazono)propanedinitrile. Levosimendan is the levo-isomer of the racemic compound simendan. It is moderately lipophilic with a small molecular weight (280.29) and is a weak acid (pKa 6.26).
Pharmacological action
β-adrenergic agonists and phosphodiesterase inhibitors produce positive inotropic effects by increasing intracellular concentrations of free calcium. This energy-dependent process involves increasing the intracellular concentration of cyclic adenosine monophosphate (cAMP). Levosimendan has a dual mechanism of action, acting as a positive inotrope and a vasodilator. The positive inotropic effect of levosimendan is achieved by calcium sensitisation rather than increasing intracellular free calcium concentration, therefore avoiding the energy-dependent process. Levosimendan binds to cardiac troponin C and stabilises the conformational changes of troponin C, facilitating actin-myosin cross-bridge formation. This binding occurs in a calcium concentration-dependent manner.
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