Which Factors Predict Placebo Response in Anxiety Disorders and Major Depression? An Analysis of Placebo-Controlled Studies of Escitalopram
J Clin Psychiatry 2006;67(11):1741-1746
© Copyright 2014 Physicians Postgraduate Press, Inc.
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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