IS ROCURONIUM AN EXCEPTION TO THE RELATION BETWEEN ONSET AND OFFSET -A COMPARISON WITH PIPECURONIUM

A general relation between the rate of onset and rate of recovery from non-depolarizing blockade has been demonstrated, with recovery consis tently about ten times slower than onset. This observation has led to the suggestion that non-depolarizing agents share a common mechanism o f action. Rocuronium, a recently introduced steroidal non-depolarizing agent, is claimed to have a very rapid onset but an intermediate dura tion and appears to test this hypothesis. To investigate this paradox we have calculated the rates of onset and recovery of rocuronium using the isolated human forearm and compared them with those of pipecuroni um. The mean ratio of recovery time/onset time for rocuronium was 31.3 , which is significantly greater than that for pipecuronium, 11.6 (P<0 .01). Whilst pipecuronium conforms to the same general relation betwee n onset and offset described previously for other non-depolarizing age nts, rocuronium appears to have a disproportionately rapid rate of ons et for its rate of recovery. This suggests that onset, recovery, or bo th onset and recovery, from rocuronium blockade occur in a different m anner to that of other non-depolarizing agents.