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J Clin Psychiatry. 2006 Nov;67(11):1741-6.

Which factors predict placebo response in anxiety disorders and major depression? An analysis of placebo-controlled studies of escitalopram.

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  • 1Department of Psychiatry, University of Cape Town, South Africa. dan.stein@curie.uct.ac.za

Abstract

BACKGROUND:

The placebo response rate has increased in several psychiatric disorders and is a major issue in the design and interpretation of clinical trials. The current investigation attempted to identify potential predictors of placebo response through examination of the placebo-controlled clinical trial database for escitalopram in 3 anxiety disorders and in major depressive disorder (MDD).

METHOD:

Raw data from placebo-controlled studies (conducted from 2002 through the end of 2004) of escitalopram in patients meeting DSM-IV criteria for MDD and anxiety disorders (generalized anxiety disorder [GAD], social anxiety disorder [SAD], panic disorder) were used. Potential predictors examined were type of disorder, location of study, dosing regimen, number of treatment arms, gender of patients, and duration and severity of disorder.

RESULTS:

Placebo response (defined as the percent decrease from baseline in the reference scale) was higher in GAD and MDD studies conducted in Europe (p < .0001 and p = .0006, respectively) and was not associated with gender or duration of episode. In GAD, the placebo response rate was higher in a European fixed-dose study, which also had more treatment arms. In SAD and in U.S. specialist-treated MDD, a higher placebo response rate was predicted by decreased baseline disorder severity.

CONCLUSION:

Additional work is needed before definitive recommendations can be made about whether standard exclusion criteria in clinical trials of antidepressants, such as mild severity of illness, maximize medication-to-placebo differences. This analysis in a range of anxiety disorders and MDD suggests that there may be instances in which the predictors of placebo response rate themselves vary across different conditions.

Comment in

  • More on placebo response. [J Clin Psychiatry. 2007]
PMID:
17196054
[PubMed - indexed for MEDLINE]
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