Escitalopram

Escitalopram is the therapeutically active S-enantiomer of RS-citalopram, a commonly prescribed SSRI. The R-enantiomer is essentially pharmacologically inactive.

Escitalopram 10 or 20 mg/day produced significantly greater improvements in standard measurements of antidepressant effect (Montgomery-Åsberg Depression Rating Scale [MADRS], Clinical Global Impressions Improvement and Severity scales [CGI-I and CGI-S] and Hamilton Rating Scale for Depression [HAM-D]) in patients with major depressive disorder (MDD) than placebo in several 8-week, placebo-controlled, randomised, double-blind, multicentre studies. Symptom improvement was rapid, with some parameters improving within 1–2 weeks of starting escitalopram treatment. In addition, escitalopram showed earlier and clearer separation from placebo than RS-citalopram, at one-quarter to half the dosage, in 8-week, placebo-controlled trials; had significantly better efficacy than RS-citalopram in a subgroup of patients with moderate MDD in a 24-week trial; and produced sustained response and remission significantly faster than venlafaxine extended release in patients with MDD. Escitalopram reduced relapse rate compared with placebo and increased the percentage of patients in remission in long-term trials (up to 52 weeks).

Consistently significant improvements for all efficacy parameters were also observed in patients with generalised anxiety disorder, social anxiety disorder and panic disorder treated with escitalopram for 8–12 weeks in individual, randomised, placebo-controlled, double-blind investigations.

Conclusions: Escitalopram, the S-enantiomer of RS-citalopram, is a highly selectiveinhibitor for the serotonin transporter, ameliorates depressive symptoms in patients with MDD at half the RS-citalopram dosage, has a rapid onset of symptom improvement and has a predictable tolerability profile of generally mild adverse events. Like RS-citalopram, escitalopram is expected to have a low propensity for drug interactions, a potential benefit in the management of patients with comorbidities. In combination, these properties place escitalopram, like other SSRIs, as first-line therapy in patients with MDD. Escitalopram is indicated for use in patients with panic disorder in Europe and, should further evidence confirm early findings that escitalopram reduces anxiety, the drug may well find an additional role in the management of anxiety disorders.

Escitalopram is the therapeutically active S-enantiomer of RS-citalopram, which is a highly selective and effective serotonin reuptake inhibitor. The antidepressant mechanism of escitalopram is presumed to be a result of stimulation of serotonergic neurotransmission in the CNS as a consequence of higher serotonin levels resulting from inhibition of the serotonin transporter.

Escitalopram has no or very low affinity for a variety of other serotonin, dopamine, α- and β-adrenergic, histamine, muscarinic and benzodiazepine receptors. It also does not bind to or has low affinity for a range of ion channels including those for Na⁺], K⁺], Cl^-] and Ca²⁺].

In rat models predictive of antidepressant activity, escitalopram demonstrated higher activity than RS- citalopram. The minimum effective dose was 4-fold lower with escitalopram than with RS-citalopram in reducing aggressive behaviour in the resident-intruder rat model and in reducing panic-like anxiety in rats after electrical stimulation of the dorsal peri-aquaductal grey matter. A trial using a conditioned fear model in rats found that escitalopram reversed suppression of exploratory activity more rapidly than a comparable dose of S-citalopram in RS-citalopram. This qualitative difference between S-citalopram and RS-citalopram was confirmed by another in vivo trial that showed higher extracellular serotonin concentrations in the frontal cortex of rats after injection with escitalopram than in rats treated with a racemic mixture of S-citalopram and R-citalopram, indicating inhibition of the S-enantiomer by the R-enantiomer in the racemate.

Escitalopram shows linear and dose-proportional pharmacokinetics with steady—state plasma concentrations achieved in 1 week in healthy volunteers. The mean steady-state area under the plasma concentration-time curve (0–24h) after a dosage of 10 mg/day was 360.2 ng · h/mL in healthy volunteers.

After a single dose of escitalopram 20mg, peak plasma concentrations were reached in 4–5 hours and were not affected by food intake. Absolute bioavailability of RS-citalopram is about 80% and binding to human plasma proteins of escitalopram is approximately 56%. The apparent volume of distribution of escitalopram after oral administration is 12–26 L/kg. The pharmacokinetic profile of the S-enantiomer is the same whether given as escitalopram 10mg or RS-citalopram 20mg.

Escitalopram is transformed to two metabolites, S-demethylcitalopram and S-didemethylcitalopram, both of which are much less potent than the parent drug. Alernatively, the nitrogen atom may be oxidised to the N-oxide metabolite. Escitalopram is the predominant plasma compound. The primary isoenzymes involved in metabolising escitalopram are cytochrome P450 (CYP) 2C19, CYP3A4 and CYP2D6.

Elimination of escitalopram is principally via hepatic and renal routes as metabolites. Oral clearance of escitalopram is 36 L/h (600 mL/min) and the elimination half-life (t1/2) is between 27 and 32 hours.

Antidepressive efficacy was observed in patients with major depressive disorder (MDD) in 8-week trials with significant improvements in Montgomery-Åsberg Depression Rating Scale (MADRS) scores in patients receiving escitalopram 10 or 20 mg/day versus those receiving placebo noted as early as 1–2 weeks after starting therapy. Follow-on studies found that escitalopram reduced the long-term risk of relapse and continued to reduce MADRS scores. Significant improvements ere also observed in all secondary efficacy parameters including the Hamilton Rating Scale for Depression (HAM-D) and the Clinical Global Impressions Improvement and Severity scales (CGI-I and CGI-S) scores, and at least half of patients receiving escitalopram responded to treatment.

Significantly greater reductions in Hamilton Rating Scale for Anxiety (HAM-A) scores were observed in 124 patients, meeting the DSM-IV criteria for generalised anxiety disorder (GAD), who received escitalopram than in 128 patients meeting the same criteria who received placebo for 8 weeks. Improvements were also observed in several secondary efficacy parameters in the patients receiving escitalopram.

In a 12-week study in patients who met the DSM-IV criteria for social anxiety disorder (SAD), those receiving escitalopram (n = 181 ) showed greater reductions in all SAD measurement scores and in disability scores than those receiving placebo (n = 177). The primary efficacy parameter was changes in Liebowitz Social Anxiety Scale scores from baseline to week 12. Secondary efficacy parameters included CGI-I scores, changes in CGI-S scores and Sheehan Disability scores over the same period.

Escitalopram was significantly more effective than placebo in the treatment of panic disorder for all efficacy parameters in a 10-week trial. Efficacy measurements included frequency of panic attacks, the Panic and Anticipatory Anxiety Scale, Panic and Agoraphobia Scale, HAM-A, CGI-I and CGI-S scores, the Patient Global Evaluation and a QOL questionnaire. Improvements were apparent by week 4 in patients with GAD or panic disorder.

Nausea and ejaculatory problems were reported in both fully published trials in patients with MDD. In addition, diarrhoea, insomnia, dry mouth, headache and upper respiratory tract infections were experienced by patients receiving escitalopram, although the incidence of these events was not significantly higher than in patients receiving placebo.

Fewer patients receiving escitalopram withdrew because of adverse events than patients treated with venlafaxine XR.

A 52-week follow-on trial found no difference in the adverse events profile for escitalopram than that observed in 8-week, double-blind studies.

The adverse events profile from three trials in patients with GAD, SAD or panic disorder receiving escitalopram was similar to that observed in patients with MDD. The withdrawal rate because of adverse events was low and similar to that of placebo.

The recommended dosage of escitalopram tor the treatment of MDD is 10 mg/day which, depending on the individual patient response, may be titrated to a maximum dosage of 20 mg/day. In Europe, escitalopram is also approved for the treatment of panic disorder; the recommended initial dosage is 5 mg/day for 1 week then titrated to 10 mg/day. The dosage may be further increased to 20 mg/ day, dependent on patient response to treatment. Administration is once daily in the morning or evening and escitalopram may be taken with or without food.

In elderly patients or patients with hepatic impairment, the maximum recommended dosage is 10 mg/day. In Europe, it is recommended that treatment be initiated at 5 mg/day in these patients. No dosage adjustment is required in patients with mild to moderate renal impairment; however, escitalopram should be used with caution in patients with severe renal impairment.

Escitalopram is contraindicated in combination with irreversible monoamine oxidase inhibitors (MAOIs) and a period of at least 2 weeks should be allowed between discontinuation of escitalopram and commencement of an irreversible MAOI and vice versa.