Prospective, multicentre, randomized, double-blind study of the efficacy of escitalopram versus citalopram in outpatient treatment of major depressive disorder

Pre-clinical studies, active-control clinical trials and meta-analyses indicate that escitalopram (S-citalopram) might be more effective than citalopram, the racemic mixture of S- and R-citalopram. The present study aimed to confirm the superior efficacy of escitalopram over citalopram. A double-blind, randomized clinical trial was performed in which general practitioners and psychiatrists compared fixed doses of escitalopram (20 mg/day) with citalopram (40 mg/day) over 8 weeks in outpatients with major depressive disorder (MDD) [baseline Montgomery-Asberg Depression Rating Scale (MADRS) score > or =30]. Primary efficacy parameter was change from baseline to last assessment in the MADRS total score. Out of 138 (aged 44.1+/-10.9 years; initial MADRS score 36.3+/-4.8) and 142 (aged 46.2+/-11.1 years; initial MADRS score 35.7+/-4.4) evaluable patients who were randomized to escitalopram and citalopram, respectively, six and 15 withdrew prematurely (P=0.05). The MADRS score decreased more in the escitalopram than in the citalopram arm (-22.4+/-12.9 versus -20.3+/-12.7; P<0.05). There were more treatment responders with escitalopram (76.1%) than with citalopram (61.3%, P<0.01). Adjusted remitter rates were 56.1% and 43.6%, respectively (P<0.05). Tolerability was similar in both groups. This randomized double-blind trial confirms that escitalopram has a superior effect to citalopram in MDD.     

Escitalopram

Escitalopram oxalate (S-citalopram, Lexapro), a selective serotonin re-uptake inhibitor antidepressant which is the S-enantiomer of citalopram, is in clinical development worldwide for the treatment of depression and anxiety disorders. Preclinical studies demonstrate that the therapeutic activity of citalopram resides in the S-isomer and that escitalopram binds with high affinity to the human serotonin transporter. Conversely, R-citalopram is approximately 30-fold less potent than escitalopram at this transporter. Escitalopram has linear pharmacokinetics, so that plasma levels increase proportionately and predictably with increased doses and its half-life of 27 - 32 h is consistent with once-daily dosing. In addition, escitalopram has negligible effects on cytochrome P450 drug-metabolising enzymes in vitro, suggesting a low potential for drug-drug interactions. The efficacy of escitalopram in patients with major depressive disorder has been demonstrated in multiple short-term, placebo-controlled clinical trials, three of which included citalopram as an active control, as well as in a 36-week study evaluating efficacy in the prevention of depression relapse. In these studies, escitalopram was shown to have robust efficacy in the treatment of depression and associated symptoms of anxiety relative to placebo. Efficacy has also been shown in treating generalised anxiety disorder, panic disorder and social anxiety disorder. Results also suggest that, at comparable doses, escitalopram demonstrates clinically relevant and statistically significant superiority to placebo treatment earlier than citalopram. Analysis of the safety database shows a low rate of discontinuation due to adverse events, and there was no statistically significant difference between escitalopram 10 mg/day and placebo in the proportion of patients who discontinued treatment early because of adverse events. The most common adverse events associated with escitalopram which occurred at a rate greater than placebo include nausea, insomnia, ejaculation disorder, diarrhoea, dry mouth and somnolence. Only nausea occurred in > 10% of escitalopram-treated patients.     

R-citalopram counteracts the antidepressant-like effect of escitalopram in a rat chronic mild stress model

The selective serotonin (5-HT) reuptake inhibitor, citalopram, is a racemic mixture of the stereoisomers, S-(+)-citalopram (escitalopram) and R-(-)-citalopram (R-citalopram). R-citalopram has been shown to counteract the 5-HT enhancing properties of escitalopram in acute studies in animals. In the present study we report, for the first time, on an interaction between R-citalopram and escitalopram after repeated dosing in a rat chronic mild stress (CMS) model of depression. The effect of escitalopram (2.0, 3.9 and 7.8 mg/kg per day), R-citalopram (7.8 mg/kg per day) and escitalopram 3.9 mg/kg per day plus R-citalopram 7.8 mg/kg per day were studied and compared to the effect of citalopram (8.0 mg/kg per day), imipramine and R-fluoxetine (8.9 mg/kg per day). Significant effects relative to a vehicle-treated group were achieved from week 1 for escitalopram (3.9 and 7.8 mg/kg per day), from week 2 for citalopram (8.0 mg/kg per day), from week 3 for R-fluoxetine (8.9 mg/kg per day) and from week 4 for escitalopram (2.0 mg/kg per day) and imipramine (8.9 mg/kg per day). R-citalopram (7.8 mg/kg per day) and escitalopram (3.9 mg/kg per day) plus R-citalopram (7.8 mg/kg per day) did not differ significantly from vehicle. There were no drug-induced effects in non-stressed control groups. In conclusion, escitalopram showed a shorter time to response in the rat CMS model of depression than citalopram, which was faster acting than R-fluoxetine and imipramine. R-citalopram counteracted the effect of escitalopram. The mechanism of action of R-citalopram is, at the moment unclear, but may be relevant to the improved clinical antidepressant activity seen with escitalopram in comparison with citalopram, and may also indicate an earlier response to escitalopram compared to other selective serotonin reuptake inhibitors (SSRIs).     

Escitalopram

Escitalopram oxalate (S-citalopram, Lexapro^?), a selective serotonin re-uptake inhibitor antidepressant which is the S-enantiomer of citalopram, is in clinical development worldwide for the treatment of depression and anxiety disorders. Preclinical studies demonstrate that the therapeutic activity of citalopram resides in the S-isomer and that escitalopram binds with high affinity to the human serotonin transporter. Conversely, R-citalopram is ～ 30-fold less potent than escitalopram at this transporter. Escitalopram has linear pharmacokinetics, so that plasma levels increase proportionately and predictably with increased doses and its half-life of 27 – 32 h is consistent with once-daily dosing. In addition, escitalopram has negligible effects on cytochrome P450 drug-metabolising enzymes in vitro, suggesting a low potential for drug–drug interactions. The efficacy of escitalopram in patients with major depressive disorder has been demonstrated in multiple short-term, placebo-controlled clinical trials, three of which included citalopram as an active control, as well as in a 36-week study evaluating efficacy in the prevention of depression relapse. In these studies, escitalopram was shown to have robust efficacy in the treatment of depression and associated symptoms of anxiety relative to placebo. Efficacy has also been shown in treating generalised anxiety disorder, panic disorder and social anxiety disorder. Results also suggest that, at comparable doses, escitalopram demonstrates clinically relevant and statistically significant superiority to placebo treatment earlier than citalopram. Analysis of the safety database shows a low rate of discontinuation due to adverse events, and there was no statistically significant difference between escitalopram 10 mg/day and placebo in the proportion of patients who discontinued treatment early because of adverse events. The most common adverse events associated with escitalopram which occurred at a rate greater than placebo include nausea, insomnia, ejaculation disorder, diarrhoea, dry mouth and somnolence. Only nausea occurred in > 10% of escitalopram-treated patients.     

R-citalopram counteracts the effect of escitalopram in a rat conditioned fear stress model of anxiety

S-citalopram (escitalopram) mediates the serotonin reuptake inhibitory effect of the racemate, R,S-citalopram. The effect of escitalopram (0.5-3.9 mg/kg) was investigated in a rat conditioned fear stress model of anxiety and compared to the effects of R-citalopram (1.0-7.8 mg/kg), R,S-citalopram (4.0 and 8.0 mg/kg), and escitalopram (2.0 mg/kg)+R-citalopram (7.8 mg/kg). Diazepam (0.95 mg/kg) and buspirone (4.6 mg/kg) were included as positive controls. During an acquisition session, rats were allowed to freely explore a novel cage for 9 min. During that time, they received two inescapable footshocks through an electrifiable grid floor. Groups of nonshocked control rats were run in parallel. During an expression session on the next day, rats were treated with drug or vehicle 30 min before they were reintroduced into the test cage for a 9-min period this time without receiving footshocks and the total distance travelled was recorded. The distance travelled by vehicle-treated rats was markedly suppressed compared to a vehicle-treated group of nonshocked controls. Escitalopram produced a dose-dependent inhibition of the conditioned suppression of exploratory behaviour (minimal effective dose 1.0 mg/kg). Interestingly R,S-citalopram 4.0 and 8.0 mg/kg produced significantly smaller effect than escitalopram 2.0 and 4.0 mg/kg, receptively. R-citalopram, 7.8 mg/kg, produced a significant effect. However, in spite of this, R-citalopram (7.8 mg/kg) significantly inhibited the effect of escitalopram (2.0 mg/kg). The activity in drug-treated nonshocked groups was similar to the vehicle-treated group, except for the buspirone-treated group where a significant reduction was observed. The finding that R-citalopram inhibits the effect of escitalopram may be relevant to the improved clinical efficacy seen with escitalopram compared to R,S-citalopram in the treatment of anxiety and depression.     

The R-enantiomer of citalopram counteracts escitalopram-induced increase in extracellular 5-HT in the frontal cortex of freely moving rats

The selective serotonin (5-HT) reuptake inhibitor, citalopram, is a racemic mixture of an S(+)- and R(-)-enantiomer, escitalopram and R-citalopram, respectively. The present study compares the effects of escitalopram, R-citalopram and citalopram on extracellular levels of 5-HT in the frontal cortex of freely moving rats. In addition, co-injection of escitalopram and R-citalopram (ratios 1:2 and 1:4) were assessed. In some experiments escitalopram and R-citalopram were infused into the frontal cortex by reverse microdialysis. Finally, the extracellular level of escitalopram in the frontal cortex was studied after administration of escitalopram alone or in combination with R-citalopram. Escitalopram (1.0-3.9 mg/kg, s.c.) produced a greater maximal increase in extracellular 5-HT than citalopram (2.0-8.0 mg/kg, s.c.). R-citalopram (15.6 mg/kg s.c.) did not affect the 5-HT levels. When co-injected, R-citalopram counteracted the escitalopram-induced increase in extracellular 5-HT levels. Local infusion of the two enantiomers into the frontal cortex produced a similar inhibitory response. R-citalopram did not influence the extracellular levels of escitalopram and therefore does not exert its effect via a pharmacokinetic interaction with escitalopram. In conclusion, the 5-HT-reuptake inhibitory activity of citalopram resides in escitalopram, and the R-enantiomer counteracts this effect. This observation would predict an improved clinical profile of escitalopram compared to citalopram.     

PET measurement of serotonin transporter occupancy: a comparison of escitalopram and citalopram

The selective serotonin reuptake inhibitor (SSRI) citalopram (R,S-citalopram) is a racemic compound of two enantiomers. On the basis of in-vitro studies, inhibition of the human serotonin transporter (5-HTT) is achieved by the S-enantiomer (S-citalopram or escitalopram). The aim of the present PET study was to compare 5-HTT occupancy after single equimolar doses (with respect to S-enantiomer) in humans in vivo using R,S-citalopram (20 mg) and S-citalopram (10 mg) using PET and the radioligand [(11)C]MADAM. The design was a single-dose, double-blind, two-way crossover study in eight healthy male subjects. The 5-HTT binding potential at baseline and after single doses of study drugs was used to calculate 5-HTT occupancy in seven brain regions. Serum concentrations of the study drugs were determined in order to calculate the apparent inhibition constant (K(i),(app)), a secondary parameter of interest for the comparison. In all brain regions examined, occupancy was numerically higher after treatment with R,S-citalopram [66+/-19% to 78+/-17% (mean+/-s.d.) depending on the region] than after S-citalopram (59+/-15% to 69+/-13%; overall comparison: F=14.8, d.f.=1, 90, p<0.001). In line with this the apparent inhibition constant was significantly lower for R,S-citalopram than for S-citalopram (overall comparison: F=6.7, d.f.=1, 90, p<0.05). The small but significant difference in occupancy and K(i),(app) found between R,S-citalopram and S-citalopram suggests that not only S-citalopram but also R-citalopram to some degree occupies the 5-HTT in the human brain in vivo.     

R-citalopram inhibits functional and 5-HTP-evoked behavioural responses to the SSRI, escitalopram

Escitalopram mediates the serotonin re-uptake inhibitory and antidepressant effect of citalopram racemate. However, recent studies have shown that R-citalopram inhibits the escitalopram-induced increase of extracellular 5-HT levels in the frontal cortex of rats. Here, we investigated the inhibitory effect of R-citalopram on the escitalopram-induced increase of 5-HT neurotransmission at the behavioural [potentiation of 5-hydroxytryptophan (5-HTP)-induced behavioural changes in mice and rats] and functional (increase in serum corticosterone in rats) levels. The effect of escitalopram was inhibited by R-citalopram in all three models, and R-citalopram, given alone, was inactive. The effects were more pronounced using an escitalopram to R-citalopram ratio of 1:4 than ratios of 1:2 and 1:1, suggesting a dose-dependent effect. The ED(50)-value of escitalopram in mouse 5-HTP potentiation studies corresponded to a serum concentration of approximately 50 ng/ml, which can be considered to be in the range of clinically relevant serum concentrations.In conclusion, R-citalopram inhibited the escitalopram-induced increase of 5-HT activity in functional, as well as behavioural, animal models. The mechanism involved in this interaction is currently unknown, but may be related to an improved clinical effect seen with escitalopram in comparison with citalopram.     

Escitalopram (10-20 mg/day) is effective and well tolerated in a placebo-controlled study in depression in primary care

Escitalopram was compared to placebo in moderately to severely depressed patients in primary care with citalopram as the active reference. Patients were randomized to receive flexible doses of 10-20 mg/day escitalopram (n=155), 20-40 mg/day citalopram (n=160), or placebo (n=154) over an 8-week double-blind period. The primary efficacy parameter was the change from baseline to last assessment in the Montgomery-Asberg Depression Rating Scale total score. Escitalopram produced a statistically significant therapeutic difference of 2.9 points (P=0.002) compared to placebo, and escitalopram was consistently and statistically significantly more efficacious than placebo from week 1 onwards. Analysis of Clinical Global Impression-Severity and Clinical Global Impression-Improvement confirmed the primary efficacy results. By week 8, significantly more patients had responded to treatment with escitalopram than with citalopram (P=0.021) or placebo (P=0.009). Escitalopram was as well tolerated as citalopram and had a similar adverse event profile. Both escitalopram- and citalopram-treated patients had placebo-level adverse event withdrawal rates (3% and 4%, respectively). This study demonstrates the consistent antidepressant efficacy and excellent tolerability of escitalopram 10-20 mg/day in primary care patients with major depressive disorder.     

Effects of risperidone augmentation in patients with treatment-resistant depression: Results of open-label treatment followed by double-blind continuation.

Approximately one-third of persons with depression do not respond to antidepressant monotherapy. Studies suggest that atypical antipsychotic augmentation may benefit these patients. We investigated the longer-term efficacy of risperidone augmentation of serotonin-selective reuptake inhibitor treatment for resistant depression. In 57 in- and outpatient centers in three countries, we conducted a three-phase study with 4-6 weeks of open-label citalopram monotherapy, 4-6 weeks of open-label risperidone augmentation, and a 24-week double-blind, placebo-controlled discontinuation phase. A total of 489 patients with major depressive disorder and 1-3 documented treatment failures entered the citalopram monotherapy phase (20-60 mg/day). Patients with <50% reduction in HAM-D-17 scores entered the risperidone augmentation phase (0.25-2.0 mg/day). Patients with HAM-D-17< or =7 or CGI-S < or = 2 were randomized to risperidone or placebo augmentation. The primary outcome was time to relapse during the double-blind phase. During citalopram monotherapy, 434 patients had <50% HAM-D-17 reduction; 299 (68.9%) were fully nonresponsive (<25% reduction) and 135 were partially nonresponsive (25-49% reduction). Of the 386 nonresponders who entered the augmentation phase, 243 remitted and 241 entered the double-blind phase. Median time to relapse was 102 days with risperidone augmentation and 85 days with placebo (NS); relapse rates were 53.3 and 54.6%, respectively. In a post hoc analysis of patients fully nonresponsive to citalopram monotherapy, median time to relapse was 97 days with risperidone augmentation and 56 with placebo (p = 0.05); relapse rates were 56.1 and 64.1%, respectively (p < or = 0.05). Open-label risperidone augmentation substantially enhanced response in treatment-resistant patients, but the longer-term benefits of augmentation were not demonstrated in this study.     

Escitalopram (S-enantiomer of citalopram): clinical efficacy and onset of action predicted from a rat model

Escitalopram is the active S-enantiomer of citalopram. In a chronic mild stress model of depression in rats, treatments with both escitalopram and citalopram were effective; however, a faster time to onset of efficacy compared to vehicle treatment was observed for escitalopram-treated (5 mg/kg/day) than for citalopram-treated (10 mg/kg/day) rats at Week 1. To study the predictability of this observation in the clinic, we analysed 4-week data from an 8-week, double-blind, randomised, placebo-controlled, flexible-dose study that compared escitalopram and citalopram to placebo in primary care patients with major depressive disorder (baseline Montgomery and Asberg Depression Rating Scale (MADRS) scores > or =22 and < or =40). Since the flexible dosing started after Week 4, analysis of 4-week data ensured that the patients received fixed doses of 10 mg/day escitalopram (155 patients), 20 mg/day citalopram (160 patients), or placebo (154 patients). The efficacy analysis showed a significantly superior therapeutic effect for escitalopram versus placebo from Week 1 onwards (observed cases) with an adjusted mean change in MADRS at Week 4 (last observation carried forward) of 2.7 points (P=0.002). By comparison, 20 mg/day citalopram did not demonstrate a statistically significant effect compared to placebo. Escitalopram was well tolerated with an adverse event profile similar to that of citalopram. The preclinical observation that escitalopram possesses a faster time to onset of efficacy than citalopram was also seen in primary care patients with major depressive disorder. Thus, escitalopram is efficacious in depression and the effect occurs earlier than for citalopram.     

R-citalopram attenuates anxiolytic effects of escitalopram in a rat ultrasonic vocalisation model

Escitalopram mediates the serotonin reuptake inhibitory effect of citalopram. To investigate the potential interactive effects between escitalopram and R-citalopram, they were studied at standard and elevated serotonin levels in a model predictive of anxiolytic activity (inhibition of footshock-induced ultrasonic vocalisation in adult rats). At standard levels, citalopram partially inhibited (64%) and escitalopram abolished (97%) vocalisation. Co-treatment with L-5-hydroxytryptophan resulted in complete inhibition with citalopram and a substantially enhanced response to escitalopram, while R-citalopram increased the vocalisation significantly. Furthermore, R-citalopram attenuated the effect of escitalopram. These findings may be relevant to the enhanced clinical efficacy seen with escitalopram compared to citalopram.     

Combination therapy with venlafaxine and carbamazepine in depressive patients not responding to venlafaxine: pharmacokinetic and clinical aspects

The chiral antidepressant venlafaxine (VEN) is both a serotonin and a norepinephrine uptake inhibitor. CYP2D6 and CYP3A4 contribute to its metabolism, which has been shown to be stereoselective. Ten CYP2D6 genotyped and depressive (F32x and F33x, ICD-10) patients participated in an open study on the pharmacokinetic and pharmacodynamic consequences of a carbamazepine augmentation in VEN non-responders. After an initial 4-week treatment with VEN (195 +/- 52 mg/day), the only poor metabolizer out of 10 depressive patients had the highest plasma concentrations of S-VEN and R-VEN, respectively, whereas those of R-O-demethyl-VEN were lowest. Five non-responders completed the second 4-week study period, during which they were submitted to a combined VEN-carbamazepine treatment. In the only non-responder to this combined treatment, there was a dramatic decrease of both enantiomers of VEN, O-demethylvenlafaxine, N-desmethylvenlafaxine and N, O-didesmethylvenlafaxine in plasma, which suggests non-compliance, although metabolic induction by carbamazepine cannot entirely be excluded. The administration of carbamazepine [mean +/- SD, range: 360 +/- 89 (200-400) mg/day] over 4 weeks did not result in a significant modification of the plasma concentrations of the enantiomers of VEN and its O- and N-demethylated metabolites in the other patients. In conclusion, these preliminary observations suggest that the combination of VEN and carbamazepine represents an interesting augmentation strategy by its efficacy, tolerance and absence of pharmacokinetic modifications. However, these findings should be verified in a more comprehensive study.     

Cost-effectiveness of escitalopram vs. citalopram in major depressive disorder

Clinical trials have shown better efficacy of escitalopram over citalopram, and review-based economic models the cost-effectiveness of escitalopram vs. citalopram (brand and generic). No head-to-head clinical trial has, however, evaluated the cost-effectiveness of both drugs so far. The aim of this study was to assess the relative cost-effectiveness of escitalopram compared with citalopram in patients with major depressive disorder. An economic evaluation was conducted alongside a double-blind randomized clinical trial conducted by general practitioners and psychiatrists comparing fixed doses of escitalopram (20 mg/day) or citalopram (40 mg/day) over 8 weeks in ambulatory care patients with major depressive disorder (baseline Montgomery-Asberg Depression Rating Scale score > or =30). Resources use was recorded using a standardized form recording use of healthcare services and days of sick leave for the 2-month prestudy period and for the 8-week study period. Statistically significant improvements were observed in patients treated with escitalopram. Mean per-patient costs for the escitalopram group, compared with the citalopram group, were 41% lower (96 euro vs. 163 euro; P<0.05) from a healthcare perspective. Differences were mostly related to lower hospitalization costs for escitalopram compared with citalopram recipients, assuming a parity price between escitalopram and citalopram. Bootstrapped distributions of the cost-effectiveness ratios also showed better effectiveness and lower costs for escitalopram compared with citalopram. Escitalopram is significantly more effective than citalopram, and is associated with lower healthcare costs. This prospective economic analysis demonstrated that escitalopram is a cost-effective first-line treatment option for major depressive disorder.     

A population pharmacokinetic model for R- and S-citalopram and desmethylcitalopram in Alzheimer’s disease patients with agitation

The citalopram for Alzheimer’s disease trial evaluated citalopram for the management for agitation in Alzheimer’s disease patients. Sparse data was available from this elderly patient population. A nonlinear mixed effects population pharmacokinetic modeling approach was used to describe the pharmacokinetics of R- and S-citalopram and their primary metabolite (desmethylcitalopram). A structural model with 4 compartments (one compartment/compound) with linear oral absorption and elimination described the data adequately. Overall, the model showed that clearance of the R-enantiomer was slower than the clearance of the S-enantiomer. Without accounting for any patient-specific covariates, the population estimate of the metabolic clearance of citalopram was 8.6 (R-citalopram) and 14 L/h (S-citalopram). The population estimate of the clearance of desmethylcitalopram was 23.8 (R-Dcit) and 38.5 L/h (S-Dcit). Several patient-specific covariates were found to have a significant effect on the pharmacokinetics of R,S-citalopram and desmethylcitalopram. A significant difference in the metabolic clearance of R-citalopram between males and females (13 vs 9.05 L/h) was identified in this analysis. Both R- and S-citalopram metabolic clearance decreased with age. Additionally, consistent with literature reports S-citalopram metabolic clearance increased with increasing body weight and was significantly influenced by CYPC19 genotype, with a difference of 5.8 L/h between extensive/rapid and intermediate/poor metabolizers. R,S-desmethylcitalopram clearance increased with increasing body weight. This model may allow for the opportunity to delineate the effect of R- and S-citalopram on pharmacodynamics outcomes related to the management of agitation in Alzheimer’s disease.     

R-citalopram functionally antagonises escitalopram in vivo and in vitro: evidence for kinetic interaction at the serotonin transporter

1. Clinical observations with the selective serotonin reuptake inhibitor (SSRI), S-citalopram, indicate that S-citalopram is more efficacious and produces earlier symptom relief than RS-citalopram. Since R-citalopram is at least 20-fold weaker than S-citalopram as inhibitor of the 5-HT transporter (SERT) in preclinical studies, the clinical data suggest an unexpected antagonistic interaction between the two enantiomers. We therefore characterised the interaction of R- and S-citalopram with the SERT in in vivo and in vitro assays. 2. In both behavioural (potentiation of 5-hydroxytryptophan (5-HTP)-induced behaviour) and electrophysiological studies (inhibition of 5-HT-elicited ion currents in Xenopus oocytes expressing the human SERT (hSERT) R-citalopram inhibited the effects of S-citalopram in a dose-dependent manner. With S-citalopram : R-citalopram ratios of 1 : 2 and 1 : 4, 5-HTP potentiation was significantly smaller than with S-citalopram alone. 3. R-citalopram did not antagonise the effects of another SSRI (fluoxetine) in either behavioural or electrophysiological studies. 4. In oocytes, inhibition of hSERT-mediated currents by R-citalopram was almost completely reversible and characterised by fast on- and off-sets of action. In contrast, the off-set for S-citalopram was 35-fold slower than for R-citalopram. 5. Kinetic analysis of the oocyte experiments suggests that S-citalopram binding to SERT induces a long-lasting, inhibited state of the transporter and that coapplication of R-citalopram partially relieves SERT of this persistent inhibition. 6. We propose that the kinetic interaction of R- and S-citalopram with SERT is a critical factor contributing to the antagonistic effects of R-citalopram on S-citalopram in vitro and in vivo.     

Altered brain concentrations of citalopram and escitalopram in P-glycoprotein deficient mice after acute and chronic treatment

According to both in vitro and in vivo data P-glycoprotein (P-gp) may restrict the uptake of several antidepressants into the brain, thus contributing to the poor success rate of current antidepressant therapies. The therapeutic activity of citalopram resides in the S-enantiomer, whereas the R-enantiomer is practically devoid of serotonin reuptake potency. To date, no in vivo data are available that address whether the enantiomers of citalopram and its metabolites are substrates of P-gp. P-gp knockout (abcb1ab (?/?)) and wild-type (abcb1ab (+/+)) mice underwent acute (single-dose) and chronic (two daily doses for 10 days) treatment with citalopram (10 mg/kg) or escitalopram (5 mg/kg) Serum and brain samples were collected 1–6 h after the first or last i.p. injection for subsequent drug analysis by an enantioselective HPLC method. In brain, 3-fold higher concentrations of S- and R-citalopram, and its metabolites, were found in abcb1ab (?/?) mice than in abcb1ab (+/+) mice after both acute and chronic citalopram treatments. After escitalopram treatment, the S-citalopram brain concentration was 3–5 times higher in the knockout mice than in controls. The results provide novel evidence that the enantiomers of citalopram are substrates of P-gp. Possible clinical and toxicological implications of this finding need to be further elucidated.     

A randomized, double-blind, 24-week study of escitalopram (10 mg/day) versus citalopram (20 mg/day) in primary care patients with major depressive disorder

OBJECTIVE: A randomized, double-blind, 24-week-fixed-dose study comparing the efficacy and safety of escitalopram to that of citalopram was safety was conducted in primary care patients with moderate to severe major depressive disorder (MDD). RESEARCH DESIGN AND METHODS: This was a randomized, double-blind, 24-week fixeddose study. Patients were randomly assigned to treatment with escitalopram 10 mg/day (n = 175) or citalopram 20 mg/day (n = 182). Clinical response was evaluated using the Montgomery-Asberg Depression Rating Scale (MADRS) and Clinical Global Impression-Severity (CGI-S) scale. The prospectively defined primary parameter of antidepressant efficacy was the change from baseline in the mean MADRS total score during the 24 weeks of double-blind treatment, using a repeated measures analysis of variance to compare the treatment groups over all assessment points simultaneously. RESULTS: Based on the primary parameter, escitalopram was at least as efficacious as citalopram. Based on the prospectively defined secondary parameter, mean change from baseline in the CGI-S score, escitalopram was statistically significantly superior to citalopram at Week 24. The importance of long-term treatment could be demonstrated, in that more than half (55% and 51%) of the patients who had not responded by Week 8 achieved remission by Week 24. Both escitalopram and citalopram were safe and well tolerated in acute and long-term treatment, and the overall adverse event profiles for the two drugs were similar. For the intent-to-treat population, there were statistically significantly fewer withdrawals in the escitalopram group than in the citalopram group, particularly after Week 8. CONCLUSION: Patients with MDD responded well to long-term treatment with either escitalopram or citalopram. This study demonstrated the importance of extending treatment of depression beyond 8 weeks.     

Higher serotonin transporter occupancy after multiple dose administration of escitalopram compared to citalopram: an [123I]ADAM SPECT study

Objectives 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 [¹²³I]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 [¹²³I]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. Conclusion 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.     

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.