Iloperidone (Fanapt®), a novel atypical antipsychotic, is a potent HERG blocker and delays cardiac ventricular repolarization at clinically relevant concentration

Abstract

QT interval prolongation on the electrocardiogram (ECG) has extensively been reported with iloperidone, a novel antipsychotic drug. The objective of the present study was to evaluate the effects of iloperidone on cardiac ventricular repolarization at three different levels; in vitro, ex vivo and in vivo. (1) In vitro level: whole-cell patch-clamp experiments were performed on HERG-transfected HEK293 cells exposed to iloperidone 0.01–1μmol/L (n=35cells, total) to assess drug effect on HERG current. (2) Ex vivo level: Langendorff retroperfusion experiments were performed on isolated hearts from male Hartley guinea pigs (n=7) exposed to iloperidone 100nmol/L with/without chromanol 293B 10μmol/L to assess drug-induced prolongation of monophasic action potential duration measured at 90% repolarization (MAPD90). (3) In vivo level: ECG recordings using wireless cardiac telemetry were performed in guinea pigs (n=5) implanted with radio transmitters and treated with a single oral gavage dose of iloperidone 3mg/kg. (1) Patch-clamp experiments revealed an estimated IC50 for iloperidone on HERG current of 161±20nmol/L. (2) While pacing the hearts at stimulation cycle lengths of 200 or 250ms, or during natural sinus rhythm (no external pacing), iloperidone 100nmol/L prolonged MAPD90 by respectively 9.2±0.9, 11.2±1.6 and 21.4±2.3ms. After adding chromanol 293B, MAPD90 was further prolonged by 7.3±3.3, 11.5±2.3 and 29.2±6.7ms, respectively. (3) Iloperidone 3mg/kg p.o. caused a maximal 42.7±10.2ms prolongation of corrected QT interval (QTcF), 40min after administration. Iloperidone prolongs the QT interval, the cardiac action potentials and is a potent HERG blocker. Patients are at increased risk of cardiac proarrhythmia during iloperidone treatment, as this drug possesses significant cardiac repolarization-delaying properties at clinically relevant concentration.