Neuromuscular Interactions between Mivacurium and Rocuronium in Rabbits

Park, Young Joo; Yoo, Hee Koo; Kim, Kyo Sang; Shim, Jae Hang

Abstract

BACKGROUND: Mivacurium has a considerably shorter duration of action than any other currently used nondepolarizing agent. Rocuronium, on the other hand, has a brief onset but an intermediate duration of action. The current study was undertaken to characterize the interaction between mivacurium and rocuronium in rabbits.
METHODS
In the first study, the dose-response relations of mivacurium, rocuronium and their combination were studied in thirty rabbits during thiopental anesthesia. Rabbits, randomly assigned to three groups (n=10), received mivacurium 10, 20, or 30 microgram/kg; rocuronium 50, 70, or 90 microgram/kg; or an equieffective combination of both drugs (0.3 ED50 mivacurium 0.3 ED50 rocuronium; 0.5 ED50 mivacurium 0.5 ED50 rocuronium; or 0.7 ED50 mivacurium 0.7 ED50 rocuronium, where ED50 is the dose producing 50% depression of the twitch height). In the second study, twenty rabbits were randomly allocated to two groups (n=10) to receive mivacurium 0.18 mg/kg or rocuronium 0.6 mg/kg. When the twitch height recovered to 25%, each rabbit received mivacurium 16.4 microgram/kg.
RESULTS
The calculated ED95 and ED50 for mivacurium were 29.1 4.2 (mean SD) and 16.4 3.3 microgram/kg, respectively. Corresponding rocuronium was 95.1 6.7 and 61.5 5.3 microgram/kg, respectively. The interaction between mivacurium and rocuronium was found to be synergistic. The measured ED50 of the mixture was only 54% of the predicted value assuming a purely additive interaction. In the second study, the times after mivacurium until 95% in mivacurium and rocuronium group were 18.1 4.6 min and 37.7 5.7 min, respectively (p<0.0001).
CONCLUSIONS
The combination of mivacurium and rocuronium is synergistic interaction and after rocuronium induced neuromuscular block, mivacurium becomes a longer acting agent than the shorter agent.