Pharmacodynamics of Rocuronium With and Without Prior Administration of Succinylcholine

Abstract

Comment Carefully controlled clinical trials are needed to establish the pharmacokinetic and pharmacodynamic behavior of new drugs to define dosing guidelines for routine use and to permit comparisons with other drugs, thereby enabling clinicians to properly “place” the new agent in their arsenal. This investigation appears to be a straightforward characterization of the kinetics of onset and offset of neuromuscular blockade with a single dose of rocuronium and in comparison with a single dose of succinylcholine. Succinylcholine clearly had a faster onset, and rocuronium had onset times typical of nondepo-larizing blockers, but the times for both drugs provided adequate intubating conditions. Importantly, the duration of rocuronium blockade was not increased by prior succinylcholine administration, and there was no evidence of cumulation. More careful reading of this paper, however, reveals a paradox: intubating times were unrelated to the onset of neuromuscular blockade. Ulnar nerve stimulation and thumb adduction force monitoring were used. The investigator/intubator was blinded and not in the operating room at the time of drug administration. When the first twitch of the train-of-four reached 80% depression (T180) the investigator was called to the operating room to perform the intubation. Times to T180 were 41 ± 15 and 70 ± 24 sec for succinylcholine and rocuronium, respectively. Times to completion of intubation were 76 ± 29 and 85 ± 23 sec for succinylcholine and rocuronium, respectively. We are faced with major questions. Why, despite significantly longer T180 times for rocuronium, was the time for completion of intubation the same? Why did it take the intubator an average of 35 sec to intubate after succinylcholine but only an average of 15 sec after rocuronium? The investigators offer some possible explanations. They state that “most succinylcholine patients felt ”tighter“ during laryngoscopy.” However, this is not supported by the data on intubation scores, which were the same in