Prolonged Respiratory Depression following Intrathecal Irrigation of Polymyxin B

It has been well recognized that certain antibiotics have a neuromuscular blocking property.We report prolonged respiratory depression following intrathecal irrigation of polymyxin B in surgical patient anesthetized G-O-halothane-d-Tc.A laminectomy was performed for 66 years female. After incision of dura surgical wound was irrigated with 1, 000, 000U. of polymyxin B in 500ml. of normal saline solution. After operation the respiration was obviously depressed. Ten hours after irrigation with polymyxin B, the serum concentration of polymyxin B was found to be 0.5U/ml. This block was not antagonized by either neostigmine or Ca2+. The artificial ventilation was necessitated for seventy-two hours.Polymyxin B potentiates the neuromuscular blockade from d-Tc but the mechanism of this action is largely unknown. It is routine practice clinically to administer neostigmine to antagonize a nondepolarizing neuromuscular blockade from d-Tc. However, in the presence of polymyxin B, neostigmine blockade should be allowed to terminate spontaneously with ventilation controlled. The neuromuscular effects of antibiotics will be accentuated when they are used in conbination with muscle relaxants.