title: Tedisamil and lidocaine enhance each other's antiarrhythmic activity against ischaemia-induced arrhythmias in rats.
abstract: 1. Combinations of the action potential-widening drug tedisamil (Class III antiarrhythmic activity), and the inactivated state sodium channel blocker lidocaine (Class Ib antiarrhythmic activity) were assessed for antiarrhythmic actions in a rat model of ischaemia-induced arrhythmias and for electrophysiological actions in normal rat myocardial tissue. 2. Both tedisamil and lidocaine dose-dependently suppressed ischaemia-induced arrhythmias. The ED(50) values were 3.0+/-1.3 and 4.9+/-0.6 micro mol kg(-1) min(-1), respectively. 3. Combinations of the two drugs acted synergistically such that the ED(50) for tedisamil was reduced to 0.8+/-0.2 micro mol kg(-1) min(-1) in the presence of 2 micro mol kg(-1) min(-1) lidocaine. Similarly, the ED(50) for lidocaine was reduced to 0.7+/-0.2 micro mol kg(-1) min(-1) in the presence of 2 micro mol kg(-1) min(-1) tedisamil (both P<0.05). 4. In a separate series of experiments in which normal ventricular tissue was electrically stimulated, 2 micro mol kg(-1) min(-1) lidocaine produced a leftward shift in the dose-response curve for tedisamil's effect on effective refractory period (P<0.05). This dose of lidocaine had no effect on its own. These data indicate that the synergistic actions of combinations of tedisamil and lidocaine were mediated, at least in part, by extension of effective refractory period in normal myocardial tissue. 5. In contrast to the strategy of developing drugs that are selective for a single electrophysiological mechanism, the results of the present study suggest that effective antiarrhythmic drugs might be developed by optimising the combination of two complimentary electrophysiological mechanisms (i.e., action potential-prolonging activity and inactivated state sodium channel blockade).
authors.affiliation: Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, 2176 Health Science Mall, Vancouver, Canada.
authors.forename: Guilda
authors.initials: G
authors.lastname: Sarraf
authors.forename: Terrance D
authors.initials: TD
authors.lastname: Barrett
authors.forename: Michael J A
authors.initials: MJ
authors.lastname: Walker
mesh_terms: D000818:Animals; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use*; D001145:Arrhythmias, Cardiac / Q000188:drug therapy* / Q000209:etiology; D001794:Blood Pressure / Q000187:drug effects; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000008:administration & dosage / Q000627:therapeutic use*; D003521:Cyclopropanes / Q000008:administration & dosage / Q000627:therapeutic use*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D004562:Electrocardiography; D007275:Injections, Intravenous; D008012:Lidocaine / Q000008:administration & dosage / Q000627:therapeutic use*; D017202:Myocardial Ischemia / Q000150:complications*; D051381:Rats
chemical_list: D018927:Anti-Asthmatic Agents; D019086:Bridged Bicyclo Compounds, Heterocyclic; D003521:Cyclopropanes; D008012:Lidocaine; C059921:tedisamil