Pharmacokinetics of azapropazone in the elderly.

Plasma concentrations of azapropazone have been measured in young and elderly subjects after a single dose of 600 mg azapropazone. Maximum concentrations were higher in the elderly. Renal function was impaired in the older subjects. Mean azapropazone clearance was significantly reduced (P less than 0.001) in the old, compared to the young. Elimination half-life was prolonged but the difference did not reach statistical significance due to the wide variation of the values in the elderly. The volume of distribution of azapropazone and degree of adipose tissue did not differ between the two groups. Azapropazone clearance correlated well with creatinine clearance (P less than 0.001) when all the subjects were included and for the younger subjects only but not for the elderly patients alone. The addition of fat mass into the regression equation improved the relationship in all groups but in the older group levels of statistical significance were not achieved. Reasons for the difference between young and old are discussed. The effects of age on the pharmacokinetics of azapropazone suggest that therapeutic plasma levels may be achieved with a dose of 600 mg daily.