Background: Because renal function affects the elimination of muscle relaxants, each new muscle relaxant must be evaluated in patients with renal failure. Accordingly, the neuromuscular effects and pharmacokinetics of rapacuronium were identified in patients with renal failure.
Methods: Rapacuronium (1.5 mg/kg) was administered to 10 healthy volunteers and 10 patients with renal failure who were undergoing non-transplant surgery, were 18-45 yr old, and were anesthetized with propofol. The adductor pollicis muscle twitch tension was monitored. Plasma samples were obtained frequently for a period of 8 h to measure the concentrations of ORG9487 and its metabolite, ORG9488. Pharmacokinetic parameters were determined using mixed-effects modeling.
Results: One patient was excluded from analysis because he was taking phenytoin chronically. Twitch depression at 1 min was less in patients than in healthy volunteers (median values: 92% in patients, 99% in volunteers). The times to 90% and peak twitch depression; to 10%, 25%, and 75% twitch recovery; and to 70% and 80% train-of-four ratios were similar in volunteers and patients. Rapacuronium's clearance was 32% less in patients with renal failure; in both groups, clearance decreased 0.909% per year of age compared with the value in a 30 yr old. The steady state distribution volume was 14% less in women than in men and 16% less in patients than in volunteers. For ORG9488, clearance was 85% less in patients than in volunteers.
Conclusions: The neuromuscular effects of a single dose of rapacuronium are affected minimally by renal failure. However, the decreased clearance of rapacuronium and its potent metabolite in renal failure suggests that repeated dosing of rapacuronium may lead to prolonged effects in patients with renal failure.