Rocuronium is considered a good candidate for rapid-sequence induction of anesthesia. Increased dose of rocuronium shortens the onset time but prolongs the duration of action. However, the ceiling effect of onset time appears when larger doses are used. Clinical trials have not shown the exact dose of ceiling effect. We performed this study to find dose producing the ceiling effect of onset time.

One hundred forty young male adults were randomized to oneof seven doses of rocuronium: 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 or 1.2 mg/kg. Anesthesia was induced with IV thiopental sodium and maintained with sevoflurane after tracheal intubation. Neuromuscular block was monitored with acceleromyography using single twitch. The onset time, the recovery of single twitch to 10% and also the changes in hemodynamics were checked.

A dose of up to 1.0 mg/kg shortens the onset time but no further decrement was seen with doses larger than 1.0 mg/kg. The recovery time was prolonged as doses were increased but there were no differences in the hemodynamics.

This study showed that in young male adults under IV induction with thiopental sodium, the ceiling effect of onset time appeared with rocuronium doses in excess of 1.0 mg/kg.