PHARMACOKINETICS OF ROCURONIUM IN ELDERLY SURGICAL PATIENTS

The effects of age on the pharmacokinetic and pharmacodynamic response s to rocuronium were studied in 20 elderly (>70 years) and 20 younger control patients (<60 years) during N2O/O2, fentanyl anaesthesia. The onset times were the same for both the elderly and younger control gro up, but the duration of action of rocuronium was significantly prolong ed in the elderly patients. Elderly patients, when compared with the y ounger, also exhibited a significant decrease in plasma clearance (3.6 7+/-1.0 vs. 5.03+/-1.5 ml kg-1 min-1, mean+/-SD) and volume of distrib ution (399+/-122 vs. 553+/-279 ml kg-1, mean+/-SD). During the recover y phase of paralysis, no significant difference was seen in the log pl asma concentration vs. twitch tension response relationship between 20 % and 80% paralysis in young and elderly patients receiving rocuronium . The differences in action of rocuronium between the elderly and youn ger groups can be fully explained by the observed differences in the d istribution and elimination of rocuronium between the two groups. The decreased total body water and decreased liver mass which normally acc ompany ageing are the probable explanation for the pharmacokinetic cha nges found in the elderly in this study. We conclude that the action o f rocuronium is prolonged in patients over 70 years of age because of decreased elimination of the drug.