Acetaminophen kinetics in the elderly

Abstract

[Acetaminophen is extensively used as an analgesic and antipyretic and is promoted as a substitute for aspirin.] Thirty-two healthy men and women, 23-78 yr old, received single 650-mg i.v. doses of acetaminophen. Kinetics were determined from multiple plasma samples drawn over the next 8-12 h. Acetaminophen elimination half-life averaged 2.7 h (range, 1.9-4.3 h) and was not related to age or sex. Distribution volume (corrected for weight) was larger in men than in women (0.99 and 0.86 l/kg) and declined with age in both sexes. This probably reflected increased fat/kg body weight in women and in the elderly, together with incomplete distribution of this nonlipophilic drug into body fat. Acetaminophen clearance declined with age in both sexes, but differences were of borderline significance. On the basis of kinetic data alone, adjustment of acetaminophen dosage for the elderly apparently was not necessary.