Plasma 10-hydroxynortriptyline in elderly depressed patients.

Plasma concentrations of nortriptyline (NT) and of unconjugated E-10-hydroxynortriptyline (E-10-OH-NT) were measured under steady-state conditions in elderly (60 yr and older) and young adult (40 yr and younger) patients treated with NT. The two groups received equivalent doses of NT. Plasma NT concentrations of the two groups did not differ, but plasma E-10-OH-NT concentrations were higher in the elderly. The plasma E-10-OH-NT/NT ratios were twice as high in the elderly group. Plasma E-10-OH-NT/NT ratios varied 2000% between individuals in the elderly group but were stable within individuals. Plasma E-10-OH-NT/NT ratios correlated positively but weakly with serum creatinine concentrations.