Class I antiarrhythmic drugs produced a spinal anesthetic effect in rats.
ABSTRACT Class I antiarrhythmic drugs are commonly used to treat cardiac rhythm disorders. Some of those drugs were recently reported to have both a cutaneous analgesic and a neural blocking effect. We evaluated whether these drugs have a spinal anesthetic effect. Three Class I antiarrhythmic drugs (class IA: quinidine, IB: mexiletine, and IC: flecainide) were tested. After they had been intrathecally injected in rats, the potencies and durations of these drugs on spinal anesthesia were recorded. Bupivacaine, a commonly used local anesthetic, and 5% dextrose solution were used as controls. Bupivacaine, flecainide, quinidine, and mexiletine produced a dose-related spinal blockade of motor function, proprioception, and nociception, but dextrose solution produced no spinal anesthetic effect. The descending order of potency was bupivacaine>flecainide>quinidine>mexiletine (p<0.05 for all differences). On an equipotent basis, flecainide, quinidine, and bupivacaine produced similar durations of action, all of which were significantly longer than that of mexiletine (p<0.05). In conclusion, intrathecal injections of Class I antiarrhythmic drugs produced a dose-related spinal anesthetic effect. These drugs may be potential candidates for developing new local anesthetics.