The onset/offset profiles of rapacuronium and succinylcholine are not identical.

To the Editor-In their article on the pharmacodynamics of rapacuro nium, Wright et at.’ stated that after a I.5-mg/kg dose, the drug’s time course of action (at the adductor pollicis) is similar to what they observed in a previous study after 1.0 mgkg of succinylcholine.2 I think this statement is somewhat misleading. Although the onset profiles of both drugs do indeed seem equivalent, the same is not true of offset. In their study, they reported a bolus to 25% recovery interval of 13.4 ? 3 .2 min after rapacuronium. This is not clinically comparable to their data for succinylcholine (8.0 t 2 min). Certainly, the recovery index noted for rapacuronium (8.8 -t 1.6 min) is far longer than the value usually cited for succinylcholine, which is at most 2-3 min. It should also be noted that 1.5 mg/kg rapacuronium represents not more than 2 times the ED,,, whereas 1.0 mg/kg succinylcholine represents 3-4 times the ED,,. Based on currently available information, rapacuronium should be viewed as a rapid-onset blocking agent of short rather than ultrashort duration. Aaron F. Kopman, M.D. Department of Anesthesiology St. Vincent’s Hospital and Medical Center of New York N e w York, N e w York 10011 [email protected]