Effect of food on acetaminophen absorption in young and elderly subjects

Twenty-four healthy volunteers aged 22 to 78 years received 650-mg doses of acetaminophen (AAP) on five separate occasions. The modes of administration were: intravenous AAP by 5-minute infusion; oral AAP as two 325-mg tablets in the fasting state; oral AAP 650 mg as an elixir preparation in the fasting state; tablets with food; and elixir with food. Plasma concentrations of AAP were determined by high-pressure liquid chromatography for up to 12 hours after the dose. In both the young and the elderly groups, the four oral modes of administration were significantly different with respect to peak plasma concentration (P less than 0.001), time to peak plasma concentration (P less than 0.001), and systemic availability (P less than 0.01). Although food slowed the rate of absorption of both oral preparations, no significant difference in peak acetaminophen plasma concentration or time of peak concentration was observed as a function of age. Absolute systemic availability of elixir and tablets in the fasting state tended to be lower in the elderly subjects (P less than 0.05). However, when either preparation was coadministered with food, there were no differences between the two age groups. Thus, age as such does not appear to be a critical determinant in the design of oral acetaminophen dosage schedules.