The Rate of Acetaminophen Metabolism in the Elderly and the Young

Twenty‐eight elderly volunteers of the 65+ age group and 28 control subjects of the 20–40 age group each received a single oral dose (1 gm) of acetaminophen in powder form. The plasma level of acetaminophen was measured over 6 hours. Plasma half‐life, clearance and relative volume of distribution of the drug were calculated. Within each age group there was a wide (threefold) range of plasma half‐life and clearance rate, with a great deal of overlap between the two groups. However, for the elderly, the group mean half‐life of acetaminophen was 2.17 hours, significantly longer than for the young (1.75 hours). The clearance rate in the elderly was significantly slower than in the young (.254 and .340 L/kg/hour respectively). There was no age‐related difference in volume of distribution of the drug by any measure, and no significant influence of sex.