Oral citalopram and reboxetine challenge tests before and after selective antidepressant treatment

Citalopram versus other anti-depressive agents for depression

BACKGROUND

Recent US and UK clinical practice guidelines recommend that second-generation antidepressants should be considered amongst the best first-line options when drug therapy is indicated for a depressive episode. Systematic reviews have already highlighted some differences in efficacy between second-generation antidepressants. Citalopram, one of the first selective serotonin reuptake inhibitors (SSRI) introduced in the market, is one of these antidepressant drugs that clinicians use for routine depression care.

OBJECTIVES

To assess the evidence for the efficacy, acceptability and tolerability of citalopram in comparison with tricyclics, heterocyclics, other SSRIs and other conventional and non-conventional antidepressants in the acute-phase treatment of major depression.

SEARCH METHODS

We searched The Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Register and the Cochrane Central Register of Controlled Trials up to February 2012. No language restriction was applied. We contacted pharmaceutical companies and experts in this field for supplemental data.

SELECTION CRITERIA

Randomised controlled trials allocating patients with major depression to citalopram versus any other antidepressants.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data. Information extracted included study characteristics, participant characteristics, intervention details and outcome measures in terms of efficacy (the number of patients who responded or remitted), patient acceptability (the number of patients who failed to complete the study) and tolerability (side-effects).

MAIN RESULTS

Thirty-seven trials compared citalopram with other antidepressants (such as tricyclics, heterocyclics, SSRIs and other antidepressants, either conventional ones, such as mirtazapine, venlafaxine and reboxetine, or non-conventional, like hypericum). Citalopram was shown to be significantly less effective than escitalopram in achieving acute response (odds ratio (OR) 1.47, 95% confidence interval (CI) 1.08 to 2.02), but more effective than paroxetine (OR 0.65, 95% CI 0.44 to 0.96) and reboxetine (OR 0.63, 95% CI 0.43 to 0.91). Significantly fewer patients allocated to citalopram withdrew from trials due to adverse events compared with patients allocated to tricyclics (OR 0.54, 95% CI 0.38 to 0.78) and fewer patients allocated to citalopram reported at least one side effect than reboxetine or venlafaxine (OR 0.64, 95% CI 0.42 to 0.97 and OR 0.46, 95% CI 0.24 to 0.88, respectively).

AUTHORS' CONCLUSIONS

Some statistically significant differences between citalopram and other antidepressants for the acute phase treatment of major depression were found in terms of efficacy, tolerability and acceptability. Citalopram was more efficacious than paroxetine and reboxetine and more acceptable than tricyclics, reboxetine and venlafaxine, however, it seemed to be less efficacious than escitalopram. As with most systematic reviews in psychopharmacology, the potential for overestimation of treatment effect due to sponsorship bias and publication bias should be borne in mind when interpreting review findings. Economic analyses were not reported in the included studies, however, cost effectiveness information is needed in the field of antidepressant trials.

Infusion of a lipid emulsion in healthy men decreases the serotonergic response

Subjects with obesity and insulin resistance display a low response to a serotonergic challenge test. One of the hallmarks of obesity and insulin resistance is elevated plasma free fatty acids (FFAs). We hypothesize that increasing plasma FFA by infusion of a lipid emulsion, may be a contributing component leading to decreased serotonergic responsivity in healthy young men. Ten lean healthy men, 23.6 ± 5.0 years and BMI 22.6 ± 1.9 kg/m(2), were included. Serotonergic responsivity was assessed using the prolactin response to infusion with citalopram, a selective serotonin reuptake inhibitor, which is a validated tool to assess serotonergic tone. All participants received a lipid/heparin emulsion (Intralipid) infusion during 6 h. Saline infusion was used as a control. To evaluate a possible effect of heparin per se on prolactin, four out of the ten subjects also received heparin only during 6 h without the serotonergic challenge test. Plasma prolactin increased by 74.3 ± 15.5% during saline infusion. Intralipid infusion increased plasma FFA from 0.5 ± 0.05 to 2.3 ± 0.2 mmol/l (p < 0.001). The increase in plasma prolactin during Intralipid infusion was significantly lower (39.3 ± 10%; p < 0.001 compared to saline infusion). Heparin infusion per se increased plasma prolactin by 14.0 ± 1.9%. We found that during the Intralipid infusion with concomitant high plasma FFA levels the serotonergic response was decreased in healthy young men. Higher FFA levels may be the mediator of the decreased serotonergic response reported in patients with insulin resistance and obesity.

Antidepressant-induced hyperprolactinaemia: incidence, mechanisms and management

Prolactin, a polypeptide hormone, is responsible, amongst other things, for milk production during lactation and breast enlargement during pregnancy. Numerous drugs can affect prolactin levels. Most commonly, conventional antipsychotics are associated with hyperprolactinaemia but there have also been reports of antidepressants causing hyperprolactinaemia. This review sets out to establish the incidence of antidepressant-induced hyperprolactinaemia, its possible mechanism and to determine appropriate remedial actions. Nearly all antidepressants are reported to be associated with hyperprolactinaemia. Incidence rates were not clearly established and symptoms were very rare. The mechanism by which antidepressants may cause hyperprolactinaemia is not fully understood, though several theories have been postulated, such as serotonin stimulation of GABAergic neurons and indirect modulation of prolactin release by serotonin. Patients taking antidepressants presenting to their clinician with symptoms potentially related to hyperprolactinaemia, such as galactorrhoea, should have their plasma prolactin level measured and their antidepressant changed if an increased prolactin level is confirmed. Routine monitoring of prolactin levels is otherwise not appropriate.

Specific effects of escitalopram on neuroendocrine response

PURPOSE

Citalopram, a selective serotonin reuptake inhibitor, is used as a neuroendocrine probe in human subjects to assess serotonin function as reflected in prolactin and plasma cortisol release. Citalopram is a racemic mixture of equal proportions of the S(+) and R(-) enantiomers. Inhibition of serotonin reuptake and, consequently, antidepressant activity is associated, almost exclusively, with the S(+) enantiomer ("escitalopram"). Studies in animal models indicate that the presence of the R(-) isomer may interfere with the serotonin reuptake activity of escitalopram. The current study compared the neuroendocrine effects of citalopram and escitalopram in healthy human volunteers.

METHODS

Plasma cortisol and prolactin levels following a single oral dose of citalopram (40 mg) or escitalopram (20 mg) were compared in samples taken every 15-30 min over a period of 240 min. Plasma citalopram concentration was determined at the same intervals.

RESULTS

Escitalopram and citalopram caused equivalent increases in plasma cortisol and prolactin. The administration of dexamethasone prior to the escitalopram challenge blocked the evoked increase in cortisol.

CONCLUSION

This is the first study to prove that a single dose of escitalopram acts centrally and not peripherally, providing further support of the use of oral escitalopram as a probe for brain serotonergic function.

Monoaminerge Funktion bei depressiven Patienten

Little is known about the variables that might predict outcome in major depression. Most studies do not imply any clinical consequences for treatment because their predictors were nonspecific and results did not differ between the different treatment options. Finding a variable that can predict the antidepressive treatment option best suited to an individual might help in reducing the considerable number of nonresponders in the treatment of depression. As most antidepressants influence the serotonergic or noradrenergic system, monoaminergic function at the start of therapy might be a possible specific response predictor. In this review, measures that can determine monoaminergic function are presented along with their relationship to treatment response, e.g., monoaminergic metabolites, neuroendocrine challenge tests, evoked event-related potentials, genetics, and neuroimaging. In conclusion, the results of serotonergic functions are still heterogeneous, but the relationship between noradrenergic function and treatment response has not been investigated in any detail yet.

Tryptophan and tyrosine availability and response to antidepressant treatment in major depression

BACKGROUND

It has been suggested that the ratio of tryptophan (TRP) and tyrosine (TYR) to other large neutral amino acids may predict response to antidepressant drugs with predominantly serotonergic compared with predominantly noradrenergic activity and that this may be clinically useful.

METHOD

147 subjects with a DSM-III-R diagnosis of major depression underwent a detailed clinical evaluation and prior to treatment had baseline measures of TRP, TYR and other large neutral amino acids (LNAA), prolactin and cortisol. Subjects entered a 6-week randomised treatment trial comparing fluoxetine and nortriptyline.

RESULTS

There was no main effect on 6-week outcome of TRP/LNAA ratio or TYR/LNAA ratio and no interaction between these factors and treatment (fluoxetine vs nortriptyline).

LIMITATIONS

Alterations in antidepressant dose were allowed therefore possibly reducing the effect of TRP or TYR availability on response.

CONCLUSIONS

Previous findings that TRP/LNAA and TYR/LNAA ratios may predict differential response to antidepressants were not replicated and neither was our previous finding of a complex relationship between TRP/LNAA and baseline prolactin in predicting 6-week response.

Basal prolactin values correlate with response to reboxetine treatment in major depression, but not with response to citalopram

Little is known about variables that might predict outcome in major depression. Recently, basal prolactin values (BPV) have been suggested to predict response to treatment with tricyclic antidepressive drugs. In order to examine whether BPV predict response to selective mono-aminergic therapy, 24 in-patients with major depression were treated in a single-masked, randomised study using the most selective noradrenergic or serotonergic reuptake inhibitors available for antidepressant treatment, i.e. reboxetine and citalopram. A significant correlation between BPV and treatment response to reboxetine was found, but not between BPV and response to citalopram. As BPV are influenced by noradrenergic activity, it can be hypothesized that depressed patients with comparatively high BPV have a relatively high noradrenergic function. This might explain why in our study depressed patients with the highest BPV responded strongest to selective noradrenergic treatment with reboxetine. As measurement of BPV is simple, further studies are suggested to examine the possible clinical value of the link between prolactin, noradrenergic function in major depression and treatment response.