title: Olanzapine prolongs cardiac repolarization by blocking the rapid component of the delayed rectifier potassium current.
abstract: Prolongation of the QT interval has been observed during treatment with olanzapine, a thienobenzodiazepine antipsychotic agent. Our objectives were 1) to characterize the effects of olanzapine on cardiac repolarization and 2) to evaluate effects of olanzapine on the major time-dependent outward potassium current involved in cardiac repolarization, namely I(Kr) (I(Kr): rapid component of the delayed rectifier potassium current).Isolated, buffer-perfused guinea pig hearts (n = 40) were stimulated at different pacing cycle lengths (150-250 msec) and exposed to olanzapine at concentrations ranging from 1 to 100 microM. Olanzapine increased monophasic action potential duration measured at 90% repolarization (MAPD90) in a concentration-dependent manner by 6.7 +/- 0.7 msec at 3 microM but by 26.0 +/- 4.3 msec at 100 microM (250 msec cycle length). Increase in MAPD(90) was also reverse frequency dependent; 30 microM olanzapine increased MAPD90 by 28.0 +/- 6.2 msec at a pacing cycle length of 250 msec but by only 18.9 +/- 2.2 msec at a pacing cycle length of 150 msec. Experiments in HERG-transfected (HERG: human ether-a-gogo-related gene) HEK293 cells (n = 36) demonstrated concentration-dependent block of the rapid component (I(Kr)) of the delayed rectifier potassium current: tail current was decreased 50% at olanzapine 3.8 microM. Olanzapine possesses direct cardiac electrophysiological effects similar to those of class III anti-arrhythmic drugs. These effects were observed at concentrations that can be measured in patients under conditions of impaired drug elimination such as renal or hepatic insufficiency, during co-administration of other CYP1A2 substrates/inhibitors or after drug overdose. These results offer a new potential explanation for QT prolonging effects observed during olanzapine treatment in patients.
authors.affiliation: Faculty of Pharmacy, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Morissette
authors.forename: Raymond
authors.initials: R
authors.lastname: Hreiche
authors.forename: Louise
authors.initials: L
authors.lastname: Mallet
authors.forename: Dean
authors.initials: D
authors.lastname: Vo
authors.forename: Edward E
authors.initials: EE
authors.lastname: Knaus
authors.forename: Jacques
authors.initials: J
authors.lastname: Turgeon
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D014150:Antipsychotic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D001145:Arrhythmias, Cardiac / Q000139:chemically induced*; D001569:Benzodiazepines / Q000008:administration & dosage / Q000494:pharmacology*; D002304:Cardiac Pacing, Artificial; D002460:Cell Line; D051668:Delayed Rectifier Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels / Q000378:metabolism; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D000077152:Olanzapine; D014162:Transfection
chemical_list: D014150:Antipsychotic Agents; D051668:Delayed Rectifier Potassium Channels; D051638:Ether-A-Go-Go Potassium Channels; D001569:Benzodiazepines; D000077152:Olanzapine