Sematilide hydrochloride (CK-1752 hydrochloride) is a selective IKr channel blocker. Sematilide causes a concentration-dependent inhibition of the delayed rectifier K+ current (IC50=25 μM). Sematilide is a class III antiarrhythmic agent.IC50 & Target: IC50: 25 μM (K+ current)In Vitro: Application of 10, 30, 100 and 300 μM Sematilide causes a concentration-dependent inhibition of the delayed rectifier K+ current (IC50=25 μM).In Vivo: Sematilide (0.3-1.0 mg/kg, intravenously i.v.) is effective in a canine model of arrhythmia[2].