title: Higher serotonin transporter occupancy after multiple dose administration of escitalopram compared to citalopram: an [123I]ADAM SPECT study.
abstract: OBJECTIVE
  Previous studies have investigated the occupancy of the serotonin reuptake transporter (SERT) after clinical doses of citalopram and other selective serotonin reuptake inhibitors. In the present study, the occupancies of SERT after multiple doses of escitalopram and citalopram were compared using the radioligand [(123)I]ADAM and single photon emission computed tomography (SPECT).
  
  
  METHODS
  Fifteen healthy subjects received escitalopram 10 mg/day (n = 6) or citalopram 20 mg/day (n = 9) for a total of 10 days. SERT occupancies in midbrain were determined with SPECT and [(123)I]ADAM at three different time points: at baseline (no medication) and at 6 and 54 h after last drug intake.
  
  
  RESULTS
  At 6 h after the last dose, mean SERT occupancies were 81.5 +/- 5.4% (mean+/-SD) for escitalopram and 64.0 +/- 12.7% for citalopram (p < 0.01). At 54 h after the last dose, mean SERT occupancies were 63.3 +/- 12.1% for escitalopram and 49.0 +/- 11.7% for citalopram (p < 0.05). The plasma concentrations of the S-enantiomer were of the same magnitude in both substances. For both drugs, the elimination rate of the S-enantiomer in plasma was markedly higher than the occupancy decline rate in the midbrain.
  
  
  CONCLUSIONS
  The significantly higher occupancy of SERT after multiple doses of escitalopram compared to citalopram indicates an increased inhibition of SERT by escitalopram. The results can also be explained by an attenuating effect of R-citalopram on the occupancy of S-citalopram at the SERT.
authors.affiliation: Department of General Psychiatry, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Nikolas
authors.initials: N
authors.lastname: Klein
authors.forename: Julia
authors.initials: J
authors.lastname: Sacher
authors.forename: Thomas
authors.initials: T
authors.lastname: Geiss-Granadia
authors.forename: Nilufar
authors.initials: N
authors.lastname: Mossaheb
authors.forename: Trawat
authors.initials: T
authors.lastname: Attarbaschi
authors.forename: Rupert
authors.initials: R
authors.lastname: Lanzenberger
authors.forename: Christoph
authors.initials: C
authors.lastname: Spindelegger
authors.forename: Alexander
authors.initials: A
authors.lastname: Holik
authors.forename: Susanne
authors.initials: S
authors.lastname: Asenbaum
authors.forename: Robert
authors.initials: R
authors.lastname: Dudczak
authors.forename: Johannes
authors.initials: J
authors.lastname: Tauscher
authors.forename: Siegfried
authors.initials: S
authors.lastname: Kasper
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001921:Brain; D002531:Cerebellum; D002928:Cinanserin / Q000031:analogs & derivatives; D015283:Citalopram / Q000493:pharmacokinetics / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D006801:Humans; D008297:Male; D008636:Mesencephalon / Q000187:drug effects* / Q000378:metabolism; D019275:Radiopharmaceuticals; D050486:Serotonin Plasma Membrane Transport Proteins / Q000187:drug effects / Q000378:metabolism*; D017367:Selective Serotonin Reuptake Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D013237:Stereoisomerism; D013997:Time Factors; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D002928:Cinanserin; D015283:Citalopram; D019275:Radiopharmaceuticals; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; C413491:2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine