Summary of Studies Showing Age-Differences in Pharmacokinetics:
Bladder Anticholinergics
The potently anticholinergic drug oxybutynin follows the trend of
increasing peak plasma levels and bioavailability with increasing age
and frailty119. This effect is so significant that
study authors suggested halving the dose of oxybutynin so older adults
to achieve the same plasma levels as younger adults. AUC and
CMax are increased 20% and 16% respectively when an
older population is given the same dose of oxybutynin as a younger
population. Moreover, solifenacin, a newer bladder anticholinergic, has
a longer t1/2 due to slower elimination and longer time
to reach CMax in older adults. This can be explained by
the slowed absorption of solifenacin in older adults which increases
their exposure to solifenacin by about 1.2-fold99. In
a study of 16 young men, 16 older men and 16 older women, receiving
either 8 mg of fesoterodine extended release or matching placebo, the
renal clearance of fesoterodine was 28% lower in older men and women
than younger men97 (table 3). This increased exposure
to fesoterodine in older adults may predict increased exposure of
tolterodine in older adults as well, as fesoterodine and tolterodine are
related compounds, with both being metabolized to the same active
ingredient.