Cumulation characteristics of cisatracurium and rocuronium during continuous infusion

The dissimilar pharmacokinetic properties of cisatracurium (CIS) and rocuronium (ROC) predict different potential for drug cumulation when these drugs are administered by continuous infusion. A study was therefore undertaken to compare cumulation potential of CIS and ROC during surgical procedures of relatively long duration (2-4 hr).

Sufentanil/propofol-N2O anesthesia was administered to 40 ASA I and II adults. In a double-blind protocol, patients were randomly allocated to receive a continuous i.v. infusion of either CIS or ROC, titrated in progressive increments or decrements as required to achieve and maintain 95 +/- 5% depression of the T1 response of the adductor pollicis muscle, using a Datex NMT-100 Relaxograph EMG monitor applied at the wrist. At the end of surgery, 60 microg x kg(-1) neostigmine plus 15 microg x kg(-1) atropine were administered for reversal.

The duration of infusion was 104 +/- 33 min in group CIS and 110 +/- 23 min in group ROC (P=NS). In both groups, a progressive decrease in potency-adjusted infusion rates was observed after 30 min, then stabilized beyond 60 min. When allowing for an initial period of stabilization, mean potency-adjusted infusion requirements were: CIS 0.81 +/- 0.02 microg x kg(-1) x min(-1) and ROC 5.58 +/- 1.94 microg x kg(-1) x min(-1). There were no differences between groups at any time with regard to potency-adjusted infusion requirements necessary to maintain 90-99% block (P=NS). However, drug costs/hr for maintenance of neuromuscular block were less with CIS ($3.57 +/- 0.09) than with ROC ($6.03 +/- 0.27), P < 0.001.

When adjusted to equipotency, infusion requirements of CIS and ROC vary at similar rates during general anesthesia. Despite pharmacokinetic differences, neither drug demonstrates cumulation for infusion lasting up to 3.5 hr.