POTENTIATION AND ANTAGONISM OF VECURONIUM BY DECAMETHONIUM

Enhancement of a vecuronium neuromuscular blockade by prior administra tion of succinylcholine has been attributed to both pharmacokinetic an d pharmacodynamic mechanisms. This study was performed to elucidate th e mechanism of this interaction using decamethonium as the agonist dru g. In five healthy patients undergoing gynecologic surgery, a cumulati ve dose-response relationship to vecuronium was determined following r ecovery from a neuromuscular block produced by 0.1 mg/kg intravenous d ecamethonium. In a second group of five similar patients, a cumulative dose-response curve to vecuronium was obtained without previous expos ure to decamethonium. In this second group, at 30% recovery from a vec uronium block, 0.1 mg/kg decamethonium was administered. The results d emonstrated a sevenfold increase in sensitivity (reducing the ED50 fro m 24 mug/kg to 3.5 mug/kg) to vecuronium when it was administered foll owing recovery from decamethonium block, and a partial reversal of the vecuronium block by decamethonium when the decamethonium was administ ered during recovery from vecuronium block. These findings support a p harmacodynamic explanation of the increased sensitivity to nondepolari zing muscle relaxants following recovery from an agonist neuromuscular block.