ArticleRoutine Therapeutic Drug Monitoring in Patients Treated with 10-360 mg/day CitalopramLe Bloc'h, Yves*; Woggon, Brigitte†; Weissenrieder, Hansjörg‡; Brawand-Amey, Marlyse*; Spagnoli, Jacques*; Eap, Chin B.*; Baumann, Pierre*Author Information *University Department of Adult Psychiatry, CH-1008 Prilly-Lausanne, Switzerland; †Psychiatric University Hospital and ‡Kantonale psychiatrische Klinik Breitenau, CH-8200 Schaffhausen, Switzerland Received May 24, 2002; accepted February 28, 2003. Address correspondence and reprint requests to Pierre Baumann, Unité de Biochimie et Psychopharmacologie, Clinique Département Universitaire de Psychiatrie Adulte, Hôpital de Cery, CH-1008 Prilly-Lausanne, Switzerland; E-mail: [email protected] Therapeutic Drug Monitoring: October 2003 - Volume 25 - Issue 5 - p 600-608 Buy Abstract From data collected during routine TDM, plasma concentrations of citalopram (CIT) and its metabolites demethylcitalopram (DCIT) and didemethylcitalopram (DDCIT) were measured in 345 plasma samples collected in steady-state conditions. They were from 258 patients treated with usual doses (20-60 mg/d) and from patients medicated with 80-360 mg/d CIT. Most patients had one or several comedications, including other antidepressants, antipsychotics, lithium, anticonvulsants, psychostimulants and somatic medications. Dose-corrected CIT plasma concentrations (C/D ratio) were 2.51 ± 2.25 ng mL−1 mg−1 (n = 258; mean ± SD). Patients >65 years had significantly higher dose-corrected CIT plasma concentrations (n = 56; 3.08 ± 1.35 ng mL−1 mg−1) than younger patients (n = 195; 2.35 ± 2.46 ng mL−1 mg−1) (P = 0.03). CIT plasma concentrations in the generally recommended dose range were [mean ± SD, (median)]: 57 ± 64 (45) ng/mL (10-20 mg/d; n = 64), 117 ± 95 (91) ng/mL (21-60 mg/d; n = 96). At higher than usual doses, the following concentrations of CIT were measured: 61-120 mg/d CIT, 211 ± 103 (190) ng/mL (n = 93); 121-200 mg/d: 339 ± 143 (322) ng/mL (n = 70); 201-280 mg/d: 700 ± 408 (565) ng/mL (n = 18); 281-360 mg/d: 888 ± 620 (616) ng/mL (n = 4). When only one sample per patient (at the highest daily dose if repeated dosages) is considered, there is a linear and significant correlation (n = 48, r = 0.730; P < 0.001) between daily dose (10-200 mg/d) and CIT plasma concentrations. In experiments with dogs, DDCIT was reported to affect the QT interval when present at concentrations >300 ng/mL. In this study, DDCIT concentration reached 100 ng/mL in a patient treated with 280 mg/d CIT. Twelve other patients treated with 140-320 mg/d CIT had plasma concentrations of DDCIT within the range 52-73 ng/mL. In a subgroup comprised of patients treated with ≥160 mg/d CIT and with CIT plasma concentrations ≤300 ng/mL, and patients treated with ≤200 mg/d CIT and CIT plasma concentrations ≥600 ng/mL, the enantiomers of CIT and DCIT were also analyzed. The highest S-CIT concentration measured in this subgroup was 327 ng/mL in a patient treated with 140 mg/d CIT, but the highest S-CIT concentration (632 ng/mL) was measured in patient treated with 360 mg/d CIT. In conclusion, there is a highly linear correlation between CIT plasma concentrations and CIT doses, well above the usual dose range. © 2003 Lippincott Williams & Wilkins, Inc.