Although the coadministration of lidocaine with propranolol interferes with the metabolic profile (pharmacokinetics), its pharmacodynamics is still unclear. In this report, we investigate whether propranolol can potentiate the effect of lidocaine. Rats received spinal anesthesia with lidocaine co-injected with propranolol. After intrathecal injections of drugs in rats, three neurobehavioral examinations (motor function, proprioception, and nociception) were performed. We showed that lidocaine and propranolol elicited a spinal blockade in motor function, proprioception, and nociception. Propranolol at the dose of 0.82μmol/kg produced no spinal anesthesia. Co-administration of lidocaine [50% effective dose (ED 50) or ED 95] and propranolol (0.82μmol/kg) produced greater spinal anesthesia than lidocaine (ED 50 or ED 95), respectively. These preclinical findings demonstrated that propranolol and lidocaine displayed spinal anesthesia. When combined with propranolol, lidocaine elicited a supra-additive effect of spinal anesthesia.
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