Description: IC50 Value: 0.43 ± 0.15 μM (Na+/K+-ATPase activity from dog kidney) [1] Istaroxime is a positive inotropic agent that mediates its action through inhibition of sodium/potassium adenosine triphosphatase (Na+/K+ ATPase). Istaroxime is an investigational drug originally patented and developed by the italian pharmaceutical company Sigma-Tau. Istaroxime is now under development for treatment of acute decompensated heart failure by CVie Therapeutics. in vitro: PST2744 inhibited the Na+/K+-ATPase activity from dog kidney with an IC50 value of 0.43 ± 0.15 μM [1]. The transient inward current (I(TI)) induced by a Ca(2+) transient in the presence of complete Na(+)/K(+) pump blockade was inhibited (-43%) by PST2744 but not by digoxin [2]. in vivo: Intravenous infusion of 0.2 mg/kg/min PST2744 in anesthetized guinea pigs exerted an immediate and long-lasting inotropic effect (ED(80) of 1.89 +/- 0.37 mg/kg) without causing lethal arrhythmias up to a cumulative dose of 18 mg/kg [1]. Istaroxime intravenous infusion (0.11 mg/kg per min) significantly increased both indices of contraction and relaxation (fractional shortening, +18+/-3.7%; aortic flow rate, +19+/-2.9%; peak myocardial systolic velocity, +36+/-7%; circumferential fiber shortening, +24+/-4.1%; peak atrial flow velocity, +69+/-8.6%; isovolumic relaxation time, +19+/-6.9%; and peak myocardial early diastolic velocity, +42+/-12%) [3]. In 5 animals, PST-2744 effects were compared with dobutamine. Heart rates, PR intervals and QT intervals were unchanged following PST-2744 administration. PST-2744 increased contractility (+dP/dt) by 56% from 1881 +/- 282 mm Hg/s to 2939 +/- 734 mm Hg/s (P < 0.01) [4]. Clinical trial: HORIZON-HF: A Phase II Trial to Assess Hemodynamic Effects of Istaroxime in Patients With Worsening HF and Reduced LV Systolic Function. Phase 2