The need for a rapid-acting non-depolarizing neuromuscular blocking agent with a short duration of action resulted in the synthesis of rapacuronium. The onset of maximum block with rapacuronium occurs in 60–90 s with doses of 1.5–2.5 mg kg−1 with a duration of clinical relaxation of 15–30 min. Rapacuronium provides clinically acceptable intubating conditions in 60 s in a majority of patients with these doses, although the conditions are somewhat inferior to those obtained with succinylcholine in lightly anaesthetized patients, such as those undergoing a rapid-sequence induction. The main drawbacks of rapacuronium are the occurrence of dose-related pulmonary side-effects (increased airway pressure and/or overt bronchospasm) and hypotension and tachycardia. The cause of pulmonary side-effects is not certain but these have been serious enough to make its worldwide introduction doubtful.

The rapid onset and offset of rapacuronium can be explained from its pharmacokinetic and pharmacodynamic characteristics. A unique property of rapacuronium is its high value for ke0, indicating a rapid access to the receptor site. The reason for this high ke0 may be related to the low intrinsic potency of rapacuronium, but this is not yet fully clarified.

Rapacuronium is a new non-depolarizing relaxant with a fast onset and rapid recovery. It was approved for the market in the United States in August 1999. The reasons for its acceptance in practice and the niche it fills are the subject of this review. Rapacuronium has been accepted wherever rapid onset and short duration of action are advantageous. It has received the greatest acceptance in brief outpatient procedures that require tracheal intubation. The average time of recovery to a train-of-four ratio of 80% is about 25 min after a usual intubating dose of 1.5 mg kg−1, when block is reversed. Its rapid onset has led some to use it in rapid-sequence induction, but the exact place in this scenario is still being defined. Its spontaneous recovery is rapid enough that many practitioners do not reverse the block if the procedure is long enough. Data suggest that this is reasonable after 60 min and may even be earlier, even 30 min, if verified by monitoring. The main adverse effects of rapacuronium are bronchospasm, hypotension and tachycardia. Of these, only bronchospasm has had significant clinical impact. These effects are dose related and the recommended dose of 1.5 mg kg−1 may keep problems to a minimum. Because rapacuronium is a new drug with unique properties its use gradually increased in its first year. Because of the problems associated with succinylcholine, rapacuronium may have advantages for brief outpatient procedures and in cases where rapid termination of block is desired, provided its adverse effects can be minimized.