PHARMACOKINETICS AND PHARMACODYNAMICS OF ROCURONIUM (ORG-9426) IN ELDERLY SURGICAL PATIENTS

The effects of age on the pharmacokinetic and pharmacodynamic response s to rocuronium (Org 9426) were studied in 20 elderly (>70 vr) and 20 younger control patients (<60 yr) during N2O/O2, fentanyl anesthesia. The onset times were the same for both the elderly and younger control group, but the duration of action of rocuronium was significantly pro longed in the elderly patients. Elderly patients, when compared with t he younger, also exhibited a significant decrease in plasma clearance (3.67 +/- 1.0 vs 5.03 +/- 1.5 mL . kg-1 . min-1, mean +/- SD) and volu me of distribution (399 +/- 122 vs 553 +/- 279 mL/kg, mean +/- SD). Du ring the recovery phase of paralysis, no significant difference was se en in the log plasma concentration versus twitch ten ion response rela tionship between 20% and 80% paralysis in young and elderly patients r eceiving rocuronium. The differences in action of rocuronium between t he elderly and younger groups can be fully explained by the observed d ifferences in the distribution and elimination of rocuronium between t he two groups. The decreased total body water and decreased liver mass which normally accompany aging are likely explanations for the pharma cokinetic changes found in the elderly in this study. We conclude that the action of rocuronium is prolonged in patients aged more than 70 y r because of decreased elimination of the drug.