Enantiomers Of Citalopram Research Articles

Cytochrome p450‐dependent disposition of the enantiomers of citalopram and its metabolites: In vivo studies in Sprague‐Dawley and Dark Agouti rats

The female Sprague-Dawley (SD) and Dark Agouti (DA) rats are considered the animal counterparts of the human extensive and poor metabolizer cytochrome P450 (CYP) 2D6 phenotypes, respectively. The aim of this work was to study possible rat strain differences in the steady-state pharmacokinetics of the (+)-(S)- and (-)-(R)-enantiomers of citalopram and its demethylated metabolites. A chronic drug treatment regimen (15 mg/kg daily) was implemented for 13 days in separate groups of SD (n = 9) and DA (n = 9) rats by using osmotic pumps. The concentrations of citalopram and two major metabolites in serum and two brain regions were analyzed by an enantioselective high-performance liquid chromatography assay. Higher serum and brain levels of citalopram and demethylcitalopram, but lower levels of didemethylcitalopram, were observed in DA rats when compared with SD rats. The enantiomeric (S/R) concentrations ratios of citalopram were lower in the DA rats when compared with the SD rats (0.53 ± 0.05 vs. 0.80 ± 0.03, P < 0.001), indicating a possibly decreased capacity in the metabolism of the (-)-(R)-enantiomer in the DA rats. This study shows that CYP2D deficiency results in steady-state pharmacokinetic differences of the enantiomers of citalopram and its metabolites.

Omeprazole preferentially inhibits the metabolism of (+)‐(S)‐citalopram in healthy volunteers

Citalopram (CITA) pharmacokinetics are enantioselective in healthy volunteers and the metabolism of (+)-(S)-CITA to (+)-(S)-DCITA is dependent on CYP2C19. Omeprazole is a potent CYP2C19 inhibitor. This study indicates that omeprazole induces a loss of enantioselectivity in the CITA pharmacokinetics because of the selective inhibition of (+)-(S)-CITA metabolism. The study assessed the influence of omeprazole on the kinetic disposition of the (+)-(S)-citalopram (CITA) and (-)-(R)-CITA enantiomers in healthy volunteers. In a cross-over study, healthy volunteers (n = 9) phenotyped as extensive metabolizers of CYP2C19 and CYP2D6 and with an oral midazolam clearance ranging from 10.9 to 149.3 ml min(-1) kg(-1) received a single dose of racemic CITA (20 mg orally) in combination or not with omeprazole (20 mg day(-1) for 18 days). Serial blood samples were collected up to 240 h after CITA administration. CITA and demethylcitalopram (DCITA) enantiomers were analyzed by LC-MS/MS using a Chiralcel OD-R column. The kinetic disposition of CITA was enantioselective in the absence of treatment with omeprazole, with the observation of a greater proportion of plasma (-)-(R)-CITA [AUC S:R ratio of 0.53 (95% CI 0.41, 0.66) for CITA and 1.08 (95% CI 0.80, 1.76) for DCITA] than (+)-(S)-CITA. Racemic CITA administration to healthy volunteers in combination with omeprazole showed a loss of enantioselectivity in CITA pharmacokinetics with an increase of approximately 120% in plasma (+)-(S)-CITA concentrations [AUC S:R ratio of 0.95 (95% CI 0.72, 1.10) for CITA and 0.95 (95% CI 0.44, 1.72) for DCITA]. The administration of multiple doses of omeprazole preferentially inhibited (+)-(S)-CITA metabolism in healthy volunteers. Although omeprazole increased plasma concentrations of (+)-(S)-CITA by approximately 120%, it is difficult to evaluate the clinical outcome because the range of plasma CITA concentrations related to maximum efficacy and minimum risk of adverse effects has not been established.

Citalopram enantiomers in plasma and cerebrospinal fluid of ABCB1 genotyped depressive patients and clinical response: A pilot study

The antidepressant activity of citalopram (R,S-CIT) is mainly due to its (S)-enantiomer (S-CIT). P-glycoprotein (P-gp), encoded by the ABCB1 gene, is a membrane transport protein which regulates the efflux of many drugs. Polymorphisms in the ABCB1 gene may have an impact on the expression and function of P-gp, thereby influencing the response to treatment with antidepressants, which are substrates of this protein. The influence of ABCB1 polymorphism on the disposition of R,S-CIT in plasma and cerebrospinal fluid (CSF) was examined under steady-state conditions in 15 patients with major depression treated with 40 mg/d R,S-CIT for 4 weeks. In contrast to the ABCB1 C3435T polymorphism, only the ABCB1 G2677T polymorphism significantly influences R,S-CIT plasma and CSF concentrations (46 ± 11 ng/ml versus 69 ± 20 ng/ml for TT versus GT/GG in plasma, p = 0.027; 24 ± 5 ng/ml versus 32 ± 9 ng/ml for TT versus GT/GG in CSF, p = 0.05). On the other hand, no significant influence of G2677T polymorphism was found on the plasma and CSF (S)/(R) ratio, suggesting a lack of stereoselectivity in the activity of this transporter. The 2677 GG/GT genotype was associated with a better treatment response ( p = 0.001) compared with 2677TT genotype. Furthermore, higher R,S-CIT plasma and CSF concentrations were observed in treatment responders. This study is the first to demonstrate that a P-gp polymorphism significantly influences plasma and CSF concentrations of R,S-CIT in depressive patients, therefore possibly influencing the activity of this antidepressant. These findings should be replicated in future studies with larger groups of patients. Because of the small number of subjects in the present study, future studies with larger groups of patients, also with different ethnicities.

The use of escitalopram beyond major depression: pharmacological aspects, efficacy and tolerability in anxiety disorders

Escitalopram, the active (S)-enantiomer of citalopram, has been approved in many countries throughout the world for the treatment of depression and anxiety disorders. It is more potent and selective than citalopram in inhibiting serotonin re-uptake in the CNS, and less potent than various other selective serotonin re-uptake inhibitors in relation to other transporter proteins and receptors: in particular, it is six times less potent than citalopram in binding to the histamine H1 and muscarinic receptors. Escitalopram has favourable pharmacokinetics: it is rapidly absorbed, has a bioavailability of 80% and is not affected by food intake. It has little potential for drug interactions: it has low protein binding and, as it is metabolised by three CYP isozymes, any impairment in the activity of one is unlikely to have a significant effect on metabolic clearance. Caution is necessary only when it is coadministered with drugs metabolised by CYP2D6, such as metoprolol, or administered to the elderly or patients with severe hepatic or renal impairment. The multiple-dose pharmacokinetics of oral escitalopram are proportional at a range of doses including its therapeutic doses. Escitalopram is approved for the treatment of a number of anxiety disorders. It seems to be well tolerated and induces few or no discontinuation symptoms, and may be considered a first-line agent for the pharmacotherapy of obsessive–compulsive disorder, generalised anxiety disorder, panic disorder and social phobia. Further studies are needed to define its activity in impulse control disorders.

The use of escitalopram beyond major depression: pharmacological aspects, efficacy and tolerability in anxiety disorders

Escitalopram, the active (S)-enantiomer of citalopram, has been approved in many countries throughout the world for the treatment of depression and anxiety disorders. It is more potent and selective than citalopram in inhibiting serotonin re-uptake in the CNS, and less potent than various other selective serotonin re-uptake inhibitors in relation to other transporter proteins and receptors: in particular, it is six times less potent than citalopram in binding to the histamine H1 and muscarinic receptors. Escitalopram has favourable pharmacokinetics: it is rapidly absorbed, has a bioavailability of 80% and is not affected by food intake. It has little potential for drug interactions: it has low protein binding and, as it is metabolised by three CYP isozymes, any impairment in the activity of one is unlikely to have a significant effect on metabolic clearance. Caution is necessary only when it is coadministered with drugs metabolised by CYP2D6, such as metoprolol, or administered to the elderly or patients with severe hepatic or renal impairment. The multiple-dose pharmacokinetics of oral escitalopram are proportional at a range of doses including its therapeutic doses. Escitalopram is approved for the treatment of a number of anxiety disorders. It seems to be well tolerated and induces few or no discontinuation symptoms, and may be considered a first-line agent for the pharmacotherapy of obsessive–compulsive disorder, generalised anxiety disorder, panic disorder and social phobia. Further studies are needed to define its activity in impulse control disorders.

Development and validation of a capillary electrophoresis method for the simultaneous determination of impurities of escitalopram including the R-enantiomer

A stereospecific capillary electrophoresis assay for the simultaneous determination of related substances and the enantiomeric purity of escitalopram was developed by a central composite face-centered factorial design and subsequently validated. Separations were carried out in a 50 μm, 47/40 cm fused-silica capillary. The optimized conditions included 20 mM phosphate buffer, pH 2.5, containing 0.5 mg/ml β-cyclodextrin and 22 mg/ml sulfated β-cyclodextrin as background electrolyte, an applied voltage of −20 kV and a temperature of 28 °C. Salicylic acid was used as internal standard. The assay was validated for the ( R)-enantiomer of citalopram and the enantiomers of the impurity citadiol in the range of 2.5–150 μg/ml and 2.5–50 μg/ml, respectively. The limit of detection was 0.02% for all compounds, the limit of quantitation 0.05%, relative to a concentration of escitalopram of 5 mg/ml. Intraday precision of migration time and peak area ratio were in the range of 0.17–0.44% and 1.64% and 6.25%, respectively. Relative standard deviations of interday precision ranged between 0.84% and 1.85% in the case of migration times and between 5.20% and 9.28% for peak area ratio. The assay was applied to the determination of the purity of escitalopram in bulk drug and tablets. ( R)-Citalopram and ( S)-citadiol were detected as impurities.

Enantioseparation and Quantitative Analysis of Citalopram by Capillary Electrophoresis with Maltose as the Chiral Selector and Its Separation Mechanism

Chiral separation of citalopram(CIT) was performed by capillary zone electrophoresis (CZE) using maltose as the chiral additive. The effect of the concentration of electrophoretic running buffer, its pH, concentration of maltose, and the applied running voltage were investigated. The optimized conditions were obtained with 20 kV as the running voltage, and a running buffer of 40 % (w/w) maltose in 8.0 × 10 −2 M phosphate (pH 5.0). Good resolution of citalopram enantiomers was achieved and the R s were 2.3 under optimal conditions. The quantitative analysis of citalopram was performed. The linear range of concentration of R-(–)-CIT to their peak areas was 0.05–4.00 mg ml −1. The LOD of the two enantiomers were 4.53 × 10 −2 mg/ml and 4.73 × 10 −2 mg ml −1, respectively. The regression coefficient was more than 0.9978. The interaction between CIT and maltose was studied by fluorescence spectra method and the mechanism of the enantioseparation was also researched. It was proved that the chiral recognition ability of maltose is related to the concentration of maltose. Maltose molecules begin to aggregate to form hydrophobic cavities, when the concentration of maltose exceeds a critical concentration. The enantioselectivity is attributed to the stereo recognition of the cavities formed by aggregating maltose molecules.

The Pharmacology of Citalopram Enantiomers: The Antagonism by R‐Citalopram on the Effect of S‐Citalopram*

Recent results on the in vivo and in vitro pharmacology of escitalopram are summarised. The exact molecular mechanism by which R-citalopram inhibits the effect of S-citalopram on the serotonin transporter remains to be elucidated. Preliminary evidence indicates an effect of R-citalopram on the association of escitalopram with the high affinity primary site, and on its dissociation from the serotonin transporter, via an allosteric mechanism. Escitalopram can be considered as an allosteric serotonin reuptake inhibitor. This serotonin dual action in binding to two sites on the serotonin transporter (both the primary site and the allosteric site) is hypothesised to be responsible for a longer binding to, and therefore greater inhibition of the serotonin transporter by escitalopram.

Sustained Citalopram Treatment in Experimental Hepatic Encephalopathy: Effects on Entrainment to the Light‐Dark Cycle and Melatonin

Patients with chronic hepatic encephalopathy often display altered diurnal rhythm as well as other affective disturbances which motivate treatment with antidepressants. We investigated the effects of sustained treatment with citalopram (10 mg/kg daily, 10 days) on 24-hr behavioural open-field activities in portacaval-shunted (PCS) rats and sham-operated control rats. In addition, the daytime and nighttime serum melatonin levels, as well as the serum concentrations of the enantiomers of citalopram and its metabolites, were analyzed. Untreated PCS rats showed reduced locomotor and rearing activities during nighttime. Citalopram treatment resulted in elevated behavioural activity in the PCS rats during night, indicative of an improved entrainment to the light-dark cycle, whereas no behavioural effect could be observed in sham rats. Higher melatonin levels in both PCS and sham rats were observed during nighttime compared with daytime, but the untreated PCS rats also showed higher daytime melatonin level than the corresponding sham group. Citalopram treatment seemed not to have any major effect on the melatonin levels. Higher serum levels of both citalopram and metabolites were observed in PCS rats as compared to sham rats. An altered ratio between the S- and R-enantiomers could also be observed in the PCS rats. In conclusion, the present data support the contention of a disturbed diurnal rhythm, and that the melatonin activity may be altered, in chronic hepatic encephalopathy. The citalopram treatment resulted in similar behavioural performances and daytime serum melatonin levels in PCS rats and controls, although pharmacokinetic differences were present between the groups.

From selective to highly selective SSRIs: A comparison of the antinociceptive properties of fluoxetine, fluvoxamine, citalopram and escitalopram

Most Serotonin Selective Reuptake Inhibitors (SSRIs) have been found to possess secondary binding properties, while citalopram and its S-enantiomer (escitalopram) have been reconfirmed “purest SSRIs”. Using the mouse model of acute pain hotplate analgesia meter, we evaluated the antinociceptive properties of fluoxetine, fluvoxamine, citalopram and escitalopram, injected i.p. Fluvoxamine induced a dose-dependent clear antinociceptive effect (with an ED 50 value of 6.4 mg/kg). Both fluoxetine and citalopram induced (separately) only a weak antinociceptive effect with an inverse “U” shape curve. All three drug's effects were not abolished by naloxone. Escitalopram did not elicit any effect at quasi-equipotent doses. These findings show that fluoxetine, fluvoxamine and citalopram given i.p. are weak antinociceptors, (not mediated through opioid mechanisms), while escitalopram possesses no antinociceptive properties when injected i.p. This difference between citalopram and escitalopram calls for further studies in order to assess the various differences between the two enantiomers of citalopram, and between each enantiomer and the racemic mixture.

Escitalopram in the treatment of generalized anxiety disorder

The selective serotonin reuptake inhibitor escitalopram is the active enantiomer of citalopram and has proven efficacy in the treatment of major depression, panic disorder and social phobia. Accumulating data indicate that it is also efficacious in the treatment of patients with generalized anxiety disorder. This drug profile summarizes the current evidence-base for the treatment of generalized anxiety disorder, describes the findings of a series of randomized placebo-controlled and comparator-controlled trials of escitalopram, examines the strengths and weaknesses of current treatment approaches and considers potential new therapies for the treatment of this common, chronic and impairing anxiety disorder. In summary, escitalopram is effective and well tolerated in both the short- and long-term treatment of generalized anxiety disorder, and has advantages over benzodiazepines and the selective serotonin reuptake inhibitor paroxetine.

Early-Phase Postmortem Redistribution of the Enantiomers of Citalopram and Its Demethylated Metabolites in Rats

The aim of this study was to investigate the early-phase postmortem redistribution of the enantiomers of citalopram (CIT) and its metabolites demethylcitalopram (DCIT) and didemethylcitalopram (DDCIT) in a rat model. Furthermore, we wanted to examine the role of the lungs as a reservoir of postmortem drug release and to investigate the influence of storage temperature (21 degrees C vs. 4 degrees C) on postmortem changes. Rats were administered a single CIT dose of 100 mg/kg (s.c.), and heart blood and lung samples were collected antemortem and 15 min postmortem for enantioselective high-performance liquid chromatographic analysis. About three times higher blood drug and metabolite levels were observed in the postmortem rats than in the antemortem rats (p < 0.0001). Refrigeration at 4 degrees C did not prevent, but significantly reduced, the postmortem increase in heart blood CIT levels as compared to the concentrations in the rats stored at 21 degrees C (p < 0.05). The lung drug concentrations were lower postmortem than antemortem (p < 0.05). The enantiomeric (S/R) concentration ratios of CIT and metabolites in blood and lungs were of similar magnitude before and after death. The parent-drug-to-metabolite ratios for CIT/DCIT were unchanged after death. In conclusion, this study shows that heart blood CIT and metabolite levels increase rapidly after death. Further, a fall in postmortem CIT concentrations in the lungs was observed, indicating that the lungs seemed to represent one major source of drug release during early-phase postmortem redistribution.

Comparison of escitalopram and citalopram efficacy: A meta-analysis

OBJECTIVEEscitalopram is a new selective serotonin reuptake inhibitor (SSRI) indicated for the treatment of major depressive disorder (MDD) and panic disorder. Escitalopram is the therapeutically active enantiomer of citalopram. Its efficacy in the treatment of MDD was compared to that of citalopram.METHODSA quantitative meta-analysis was applied to 1262 patients in four randomised clinical trials; the comparison was based on response rate and mean change from baseline in the Montgomery–Åsberg depression rating scale (MADRS) total score at week 8. Complementary analyses were performed on early MADRS change from baseline (week 1), in very severely depressed patients (baseline MADRS total score ≥35) and on the influence of the level of severity at baseline.RESULTSCompared with citalopram, escitalopram-treated patients showed significantly higher response rates and increased mean change from baseline in MADRS at weeks 1 and 8. The superiority of escitalopram over citalopram was more pronounced in very severely depressed patients. This superiority was further shown to increase with degree of severity of the depression. The robustness of meta-analysis results was supported by sensitivity analyses. The clinical superiority of escitalopram versus citalopram is consistent with the results of preclinical pharmacological studies.CONCLUSIONEscitalopram was shown to be an effective therapeutic treatment for MDD, presenting significant advantages over citalopram.

Routine therapeutic drug monitoring in patients treated with 10-360 mg/day citalopram.

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 > or =160 mg/d CIT and with CIT plasma concentrations < or =300 ng/mL, and patients treated with < or =200 mg/d CIT and CIT plasma concentrations > or = 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.

Metabolism of citalopram enantiomers in CYP2C19/CYP2D6 phenotyped panels of healthy Swedes.

To investigate pharmacokinetics of the enantiomers of citalopram (CT) and its metabolites desmethylcitalopram (DCT) and didesmethylcitalopram (DDCT) in Swedish healthy volunteers in relation to CYP2C19 and CYP2D6 geno- and phenotypes. Racemic CT was given for seven days to panels with different genotypes and the following mephenytoin (Me) and debrisoquine (De) hydroxylation phenotypes: EMDe/EMMe, PMDe/EMMe, EMDe/PMMe (n = 6 in all groups), and one PMDe/PMMe subject. Blood sampling was carried out during day 7, and all urine was collected for 12 h after the last dose of CT. The AUC of S-CT was significantly higher in the EMDe/PMMe panel compared to the EMDe/EMMe and PMDe/EMMe panels (P < 0.05), whereas the AUC of R-CT did not differ between the panels. Similar differences, although they did not reach statistical significance, were noted for S-DCT and R-DCT. The enantiomers of DDCT were not quantifiable in PMDe, and there was no difference in DDCT enantiomer concentrations between the other two panels. A PMDe/PMMe subject stopped taking CT after five days due to severe adverse effects. Based on two time points, this subject had a very long CT half-life of 95 h. The value of 1.0 for the S/R ratio of the CT trough in this subject was similar to the mean S/R CT trough ratio of the EMDe/PMMe panel, but higher than the S/R CT ratio of the EMDe/EMMe panel (0.56; 95% CI 0.49-0.63) and the PMDe/EMMe panel (0.44; 95% CI 0.31-0.57). Thus the latter two phenotypes eliminated S-CT more rapidly via CYP2C19. An adverse effect described as an 'alcohol hangover' feeling was reported by one subject from each of the three panels. These individuals had the highest concentrations of both CT enantiomers. The AUC of S-, but not R-(CT) was found to be significantly higher in PM of mephenytoin compared to EMs, PMs may need a lower dosage of CT.

Stereospecific determination of citalopram and desmethylcitalopram by capillary electrophoresis and liquid-phase microextraction

A chiral capillary electrophoresis (CE) system allowing simultaneous enantiomer determination of citalopram (CIT) and its pharmacologically active metabolite desmethylcitalopram (DCIT) was developed. Excellent chiral separation was obtained using 1% sulfated-β-cyclodextrin (S-β-CD) as chiral selector in combination with 12% ACN in 25 mM phosphate pH 2.5. Samples were prepared by liquid-phase microextraction (LPME) based on a rodlike porous polypropylene hollow fibre. CIT and DCIT were extracted from 1 ml plasma made alkaline with NaOH, into dodecyl acetate impregnated in the pores of a hollow fibre, and into 20 mM phosphate pH 2.75, inside the hollow fibre. The acceptor solution was directly compatible with the CE system. Efficient sample clean-up was seen, and the recoveries were 46 and 29% for the enantiomers of CIT and DCIT, respectively, corresponding to 31 and 19 times enrichment. The limit of quantification (S/N=10) was <11.2 ng/ml, intra-day precision was <12.8% RSD, and inter-day precision was <14.5% RSD, for all enantiomers. The validated method was successfully applied to simultaneous determination of enantiomer concentrations of CIT and DCIT in plasma samples from nine patients treated with racemic citalopram. The results confirm LPME-CE as a suitable and promising tool for enantiomeric determination of chiral drugs and metabolites in biological matrices.

Stereoselective single-dose kinetics of citalopram and its metabolites in rats.

The single-dose kinetics of the enantiomers of citalopram (CIT) and its metabolites, demethylcitalopram (DCIT) and didemethylcitalopram (DDCIT), were investigated after administration of 10, 20, or 100 mg/kg (s.c.) rac-CIT to rats. Samples from serum and two brain regions were collected 1, 3, 10, or 20 h postdose for HPLC analysis. In the 100 mg/kg rats, the enantiomeric (S/R) serum concentration ratios of CIT decreased during the study period (0.93 at 1 h vs. 0.59 at 20 h; P < 0.001). In the 10 and 20 mg/kg rats, the decrease in serum S/R CIT ratios was not so evident as in the 100 mg/kg rats. In all three groups the S/R CIT ratio was almost the same in the brain as in serum, although both CIT enantiomer levels in the brain were found to be 5-10 times higher than the levels in serum. The serum and brain metabolite levels were low in the 10 and 20 mg/kg rats, whereas the levels increased during the study period in the 100 mg/kg rats. In conclusion, the CIT enantiomers were shown for the first time to be stereoselectively metabolized after single-dose administration to rats, as previously shown in steady-state dosing studies in humans and rats.

Enantioselective analysis of citalopram and metabolites in adolescents.

Studies of the antidepressant effect and pharmacokinetics of citalopram have been performed in adults, but the effects on children and adolescents have only been studied to a minor extent despite its increasing use in these age groups. The aim of this study was to investigate a group of adolescents treated for depression, with respect to the steady-state plasma concentrations of the enantiomers of citalopram and its demethylated metabolites desmethylcitalopram and didesmethylcitalopram. Moreover, the authors studied the genotypes for the polymorphic cytochrome P450 enzymes CYP2D6 and CYP2C19 in relation to the different enantiomers. The S/R ratios of citalopram and desmethylcitalopram found in this study of 19 adolescents were similar to studies involving older patients. The concentrations of the R-(-)- and S-(+)-enantiomers of citalopram and desmethylcitalopram were also in agreement with values from earlier studies, the R-(-)-enantiomer (distomer) being the major enantiomer. The results indicate that the use of oral contraceptives may have some influence on the metabolism of citalopram. This might be because of an interaction of the contraceptive hormones with the CYP2C19 enzyme.

Optimization and characterization of the chiral separation of citalopram and its demethylated metabolites by response-surface methodology

Response-surface modelling and sequential optimization have been used for optimization and characterization of the separation of the enantiomers of citalopram, desmethylcitalopram, and didesmethylc ...

Stereoselective HPLC-assay for citalopram and its metabolites.

The racemic selective serotonin reuptake inhibitor citalopram (CIT) is increasingly used for depressive disorders. As both enantiomers of CIT differ in pharmacologic activity and demethylated metabolites might contribute to the antidepressent action of CIT, a stereoselective assay for all active compounds is needed, but will require that pharmacokinetic/pharmacodynamic relationships be investigated. A stereoselective high-performance liquid chromatography (HPLC)-assay (Chirobiotic V column) with UV-detection (lambda = 240 nm) for R- and S-CIT as well as both enantiomers of desmethyl(DM)-CIT and didesmethyl(DDM)-CIT was developed. The calibration range was linear from 5 to 200 ng/mL and the lower limit of detection averaged 2 ng/mL. Based on three quality controls (10, 75, and 150 ng/mL) the intraday and interday coefficients of variation ranged from 1.3% to 9.0% for CIT and from 2.2% to 10.3% for DM-CIT and DDM-CIT. The assay was used to analyze the trough steady state plasma levels of all 6 agents in 16 elderly patients treated daily with 20 to 40 mg CIT. For the dose of 20 mg (n = 14) mean values +/- SD of R- (and S-CIT) averaged 36.2+/-15.0 (27.4+/-13.1) ng/mL, respectively (mean R/S-ratio: 1.4+/-0.4), for R- (and S-DM-CIT) 7.2+/-3.1 (7.7+/-3.8) ng/mL, respectively (R/S-ratio: 1.0+/-0.3) whereas DDM-CIT was only detectable as R-enantiomer in 8 cases (13.2+/-12.1 ng/mL; range: 2.2-36.2 ng/mL). Significant (p < 0.01) linear correlations could be found between both enantiomers of CIT and DM-CIT as well as between parent drug and primary metabolite for the R-enantiomers. Apparently R/S- and metabolic ratios increased with dose; this might indicate that stereoselective disposition of CIT and DM-CIT is concentration-dependent. The present assay allows a rapid, sensitive, and reliable stereoselective determination of CIT and its (active) metabolites which can be applied for assessing pharmacokinetic parameters and evaluating putative relationships to clinical (side) effects.