Kinetics of citalopram in elderly patients

The kinetics of the antidepressant drug citalopram, a specific 5-HT uptake inhibitor, has been investigated in 11 elderly patients (age 73-90) and compared to previous data from younger patients and volunteers. The recorded steady state citalopram levels of 140-545 nM after a once-daily 20-mg dose were up to four times higher than expected from data in younger patients and volunteers. The biological half-life (1.5-3.75 days) and estimated systemic clearance (0.08-0.3 1/min) also differed from data in younger individuals (1.5 days and 0.4 1/min, respectively). Clearance values generally decreased with increasing age. Drug/metabolite ratios were higher in patients with the longest half-lives and lowest citalopram clearance, indicating reduced metabolic activity. No reduction in renal clearance was indicated by urine data, obtained for two of the patients. The study suggests that daily doses of 5-20 mg give approximately the same steady state plasma levels in elderly patients as doses of 40 mg in younger, and that this is due to reduced rates of metabolism in the elderly.