To the Editor:—

Rapacuronium is marketed as an alternative to succinylcholine for rapid sequence induction, especially in the pediatric population. Recently, we had to administer anesthesia to a 5-yr-old child (weight, 22 kg) considered to have a full stomach. A general anesthetic was planned with a rapid sequence induction using thiopental and rapacuronium. Thiopental (4 mg/kg) was injected, and immediately after the 22-gauge intravenous line was visibly cleared of thiopental, rapacuronium (1.5 mg/kg) was injected. Rapacuronium and thiopental precipitated in the intravenous line, making it inoperative.

Precipitation has been observed with thiopental and other depolarizing and nondepolarizing muscle relaxants, including succinylcholine, rocuronium, vecuronium, and pancuronium. 1,2The mechanism seems to be a pH-dependent decrease in the solubility of thiopental. 1,3Similarly, the differing pH of rapacuronium (pH 3.9) and thiopental (pH 10.6) may explain the observed precipitation. The complications of this interaction are serious and we would like to inform our colleagues about it.

Chambi D, Omoigui D: Precipitation of thiopental by some muscle relaxants (letter). Anesth Analg 1995; 81: 1112
Taniguchi T, Yamamoto K, Kobayashi T: The precipitate formed by thiopentone and vecuronium. Can J Anaesth 1996; 43: 511–3
Morton WD, Lerman J: The effect of pancuronium on the solubility of aqueous thiopentone. Can J Anaesth 1987; 34: 87–9