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Toshi A Furukawa a Department of Psychiatry, Nagoya City University
Medical School, Nagoya 467-8601, Japan, b Cochrane Collaboration Depression,
Anxiety, and Neurosis, Health Services Research, King's College
Institute of Psychiatry, London SE5 8AF, c Department of
Medicine and Public Health, Section of Psychiatry, University of
Verona, Ospedale Policlinico 37134 Verona, Italy Correspondence to: T A
Furukawa furukawa{at}med.nagoya-cu.ac.jp
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Abstract |
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Objective:
To compare the effects and side effects of low dosage tricyclic antidepressants with placebo and with standard dosage tricyclics in acute phase treatment of depression.
Design:
Systematic review of randomised trials
comparing low dosage tricyclics (
100 mg/day) with placebo or with
standard dosage tricyclics in adults with depression.
Main outcome measures:
Relative risk of response in
depression (random effects model), according to the original authors'
definition but usually defined as 50% or greater reduction in severity
of depression. Relative risks of overall dropouts and dropouts due to
side effects.
Results:
35 studies (2013 participants) compared low dosage tricyclics with placebo, and six studies (551 participants) compared low dosage tricyclics with standard dosage tricyclics. Low
dosage tricyclics, mostly between 75 and 100 mg/day, were 1.65 (95%
confidence interval 1.36 to 2.0) and 1.47 (1.12 to 1.94) times more
likely than placebo to bring about response at 4 weeks and 6-8 weeks,
respectively. Standard dosage tricyclics failed, however, to bring
about more response but produced more dropouts due to side effects than
low dosage tricyclics.
Conclusions:
Treatment of depression in adults with
low dose tricyclics is justified. However, more rigorous studies are needed to definitively establish the relative benefits and harms of
various dosages.
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What is already known on this topic
Experts have often claimed that clinicians prescribe tricyclics at less than adequate dosages What this study adds
They may or may not be as effective as standard dosage tricyclics but result in fewer dropouts due to side effects The minimum effective dosage and ranges for antidepressants has not
been established |
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Introduction |
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Despite the growing popularity of selective serotonin reuptake inhibitors and other newer antidepressants, tricyclic andtidepressants are still extensively prescribed worldwide. In the United Kingdom between 1991 and 1996, there was a 460% increase in prescriptions for selective serotonin reuptake inhibitors, but there was also a 40% increase in prescriptions for tricyclics for patients starting treatment, with these new patients still outnumbering those taking selective serotonin reuptake inhibitors by 56%.1 In the United States between 1990 and 1995 antidepressant use increased by 73% mainly because of patients being prescribed selective serotonin reuptake inhibitors, but even today tricyclics are prescribed as often as selective serotonin reuptake inhibitors. 2 3 Other countries show similar trends.4
Evidence for the recommended dosage of tricyclics is
poor.
5 6
Many of the existing guidelines recommend
dosages greater than 100 mg/day or 125 mg/day, but there is a lack of
convincing evidence that lower dosages are not
effective.
7 8
This uncertainty casts doubt on the widely
held view that depression is undertreated both in primary care and in
psychiatric settings.
9 10
It also questions whether
selective serotonin reuptake inhibitors should be preferred over
tricyclics when controlled trials failed to find differences in
effectiveness between the two, because it is easier to achieve
"adequate" dosage with selective serotonin reuptake
inhibitors.11
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Methods |
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Inclusion criteria
We included randomised trials comparing low dosage
tricyclics with placebo or with standard dosages of the same tricyclic
in the acute phase treatment of adults with depression. Low dosage was
defined as 100 mg/day or less of imipramine, amitriptyline, clomipramine, desipramine, doxepin, dothiepin, trimipramine, or lofepramine. We excluded nortriptyline because the standard dosage is
debatable. Standard dosage was defined as greater than 100 mg/day. Our
trial was to last at least four weeks.
Our primary outcome was the effect of treatment on depression, according to the original authors' definition but usually defined as 50% or greater reduction in severity of depression. The severity of symptoms was measured by either observer rating (preferred) or self report.
Identification of trials
We electronically searched the Cochrane Collaboration depression, anxiety, and neurosis controlled trials register up to
November 2000 for any trials in which tricyclics were given. This
database incorporates results of group searches of Medline (1966 onwards), Embase (1980 onwards), CINAHL (1982 onwards), PsycINFO (1974 onwards), PSYNDEX (1977 onwards), and LILACS (1982-99). We also hand
searched the major psychiatric and medical journals. Two reviewers (HM
and TAF) then manually examined the potential papers to see if they
were randomised trials comparing low dosage tricyclics with placebo or
with standard dosage for any form of depression. All potential
identified papers were then checked according to the strict eligibility
criteria by two independent reviewers (TAF and CB).
To identify further reports TAF checked the references of this preliminary list of selected studies along with references of other relevant review papers. To identify more recent reports HM subjected nine of the most representative studies to SciSearch. TAF contacted authors of major papers and other experts in the specialty.
Quality assessment and data extraction
TAF and CB assessed the methodological quality of the selected
studies. The criteria for quality assessment were based on the
recommendations of the Cochrane Collaboration Handbook and
focused on concealment of allocation and double
blinding.12 HM and TAF independently extracted data from
the original reports using data extraction forms. Disagreements between
the two reviewers were resolved by consensus.
Statistical analysis
Data were entered twice into Review Manager (version 4.1) using
the duplicate data entry facility. For dichotomous outcomes, we
calculated relative risks and their 95% confidence intervals with a
random effects model because they may be more generalisable and more
easily interpreted than those obtained with fixed effects models, odds
ratios, or risk differences.
13 14
We assessed
heterogeneity between studies with the Q statistic and by visual
inspection of the results. For continuous outcomes, we calculated
standardised weighted mean differences with a random effects model.
We first performed per protocol analysis according to the values reported by the original authors. When data on dropouts were included by the last observation carried forward method, we analysed them according to the primary studies. We also performed a worst case scenario intention to treat analysis whereby dropouts were considered non-responders in the active treatment group but as responders in the placebo group. This extreme scenario was to guard against favouring active drugs that could be the more harmful.
We performed a funnel plot analysis to check for publication bias. To examine the robustness of the findings we performed two sensitivity analyses, by limiting the included studies to those using operational diagnostic criteria for major depression and to those in which the dosage was 75 mg/day or less.
Subgroup analyses should be performed and interpreted with caution because multiple analyses lead to false positive conclusions. We did, however, perform two subgroup analyses, where possible: for older people (age 65 or more) separately, because these people may be more vulnerable to side effects associated with tricylics and a decreased dosage is often recommended for them; and for psychiatric patients and primary care patients separately, because it is sometimes believed that results obtained from either of these settings may not be straightforwardly applicable to the other setting.
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Results |
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Study inclusion and characteristics
Of the 2418 citations originally identified in our electronic
search, 141 were potentially relevant and were assessed
for strict eligibility and quality. The inter-rater reliability of the
two reviewers for this first stage of study selection was good
(agreement 97%,
=0.61). After the reference search, SciSearch, and personal contacts, we ultimately agreed on 35 studies (2013 participants) that compared low dosage tricyclics with placebo, and six
studies (551 participants) that compared low dosage tricyclics with
standard dosage tricyclics. Two of these had three arms of standard
dosage tricylics, low dosage tricylics, and placebo (fig 1). The
inter-rater reliability for this second stage of assessment for
eligibility and validity was excellent, with weighted kappas between
0.58 and 0.86. The inter-rater reliability of the two validity criteria
was also satisfactory, with weighted kappas of 0.58 and 0.79, respectively.
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Sixteen studies used amitriptyline as active drugs and 13 used imipramine. The remaining randomised controlled trials studied clomipramine (3 trials), doxepine (3), dothiepin (2), trimipramine (2), and lofepramine (1). Five studies focused on depression in people aged 65 or more. Ten studies were conducted in primary care and 12 studies in psychiatric settings. Six studies dealt with depression seen in patients with comorbid physical conditions such as migraine or rheumatoid arthritis. All of the included studies were randomised controlled trials with both patients and doctors blinded (table; the complete list of included studies is also available in the Cochrane Library). However, only four studies reported enough details on their randomisation procedure.
Low dosage tricyclics versus placebo
Effectiveness
Low dosage tricyclics, on average between 75 and 100 mg/day, were
65% (36% to 100%; random effects model), 47% (12% to 94%), and
114% (41% to 226%) more likely than placebo to bring about response
at 4 weeks, 6-8 weeks, and 3-12 months, respectively. On average 45%
of patients taking low dosage tricyclics responded at 4 weeks, 59% at
6-8 weeks, and 53% at 3-12 months. Heterogeneity was noted only for
the outcome at 6-8 weeks (fig 2).
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Acceptability
No difference was found in total number of dropouts between low
dosage tricyclics and placebo groups (relative risk 1.08, 0.93 to
1.26). Overall, 439 of 1840 (24%) enrolled participants dropped out by
the end of the trial. People taking low dosage tricyclics, however,
were 111% (35% to 228%) more likely than those taking placebo to
drop out due to side effects. People taking low dosage tricylics were
also 63% (36% to 95%) more likely to experience at least one side effect.
Funnel plot analysis and sensitivity analyses
The funnel plot showed some publication bias because the five
smallest studies reported large relative risks in favour of low dosage
tricyclics. These studies mainly dated from the 1960s and `70s and
involved patients recruited outside a clinical setting. When we omitted
these studies the plot was no longer asymmetrical and the relative risk
decreased only slightly from 1.65 (1.36 to 2.00) to 1.58 (1.31 to 1.90)
at 4 weeks, and from 1.47 (1.12 to 1.94) to 1.28 (1.05 to 1.55) at 6-8 weeks. The outcome at 6-8 weeks was no longer heterogeneous. The pooled standardised mean difference for the continuous outcome changed to
-0.31 (-0.47 to -0.15) at 4 weeks and -0.32 (-0.49 to -0.15) at
6-8 weeks; these results were also no longer heterogeneous.
Subgroup analyses
Based on these sensitivity analyses, we did not need to restrict
ourselves to studies employing operational diagnostic criteria or to
those that administered strictly low dosage tricyclics to arrive at
conclusions generalisable to present day patients. The following
subgroup analyses therefore deal with studies treating any depression.
Only five studies explicitly dealt with
depression in people aged 65 or more (n=265). Due to lack of power,
the meta-analysis of these five studies produced only the following significant findings. The people taking low dosage tricyclics were more
likely to show response at 6-8 weeks than those taking placebo, but
they were also more likely to experience at least one side effect
(relative risk 1.52, 1.09 to 2.11 and 1.26, 1.10 to 1.45, respectively). The point estimates of the obtained relative risks and
standardised mean differences were in accordance with the overall results.
Primary care settings
Five studies recruited patients with
depression in primary care settings; five further studies included patients with various physical conditions such as migraine, low back
pain, and rheumatoid arthritis, presumably in primary care settings.
Overall there were 558 participants. Although there were no significant
findings in the random effects estimates of our primary outcome, the
resulting 95% confidence intervals were compatible with the overall
findings. For example, at 4 weeks participants taking low dosage
tricyclics were 28% (-2% to 68%; random effects model) more likely
to show response than those taking placebo; at 6-8 weeks, participants
taking low dosage tricyclics were 23% (-3% to 55%) more likely to
do so. The continuous outcomes were again supportive of the overall
conclusions because the standardised mean difference was -0.29 (-0.58
to 0.01) at 4 weeks and -0.41 (-0.62 to -0.19) at 6-8 weeks.
Psychiatric settings
We also performed a meta-analysis on
only such studies that made clear that they were conducted with patients seen in psychiatric settings and not comorbid with other major
psychiatric disorders such as eating disorders or Alzheimer's disease.
Twelve studies (n=912) were available; two with inpatients and the
others with outpatients.
Among the psychiatric patients, the relative risk for showing
response with low dosage tricyclic rather than with placebo was 2.40 (1.11 to 5.16; random effects model) at 2 weeks, 1.89 (1.24 to 2.87) at
4 weeks, 1.66 (0.87 to 3.15) at 6-8 weeks, and 2.06 (1.34 to 3.17) at 6 months. The standardised mean difference also supported the
effectiveness of low dosage tricyclics in psychiatric patients with
depression. Exclusion of the outliers lessened heterogeneity associated
with some of the results but did not substantially affect the relative
risks or standardised mean differences. The tricyclic was more likely
to cause dropouts due to side effects or at least one side effect
(relative risk 3.80, 1.63 to 8.86 and 1.43, 1.19 to 1.73, respectively)
than placebo.
Low dosage tricyclics versus standard dosage tricyclics
Effectiveness
Standard dosage tricyclics were not significantly more effective
at achieving response than low dosage tricyclics at 1-8 weeks (fig 4):
relative risk 0.89 (0.74 to 1.07) at 4 weeks and 1.11 (0.76 to 1.61) at
6-8 weeks. In terms of the standardised mean difference, standard
dosage tricyclics outperformed the low dosage tricyclics at 4 weeks
only (standardised weighted mean difference 0.29, 0.08 to
0.50).
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Acceptability
Overall there was no difference in the acceptability of the
treatments when measured by leaving study early for any reason
(relative risk 0.95, 0.75 to 1.20). Low dosage regimens, however, were
55% (24% to 73%) less likely than standard dosage regimens to cause
dropouts due to side effects.
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Discussion |
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Low dosage tricyclic antidepressants between 75 and 100 mg/day and possibly below this range brings about more reduction in depression at 4-8 weeks of treatment and beyond, as well as more dropouts due to side effects and more people with at least one side effect than placebo in both primary care and psychiatric settings. Given the average event rates for controls in the included studies, the number needed to treat to bring about response in depression was between 4 and 6 at 1-6 months of treatment, and the number needed to harm to produce one dropout due to side effects was around 24. Standard dosage tricyclics, however, may or may not be able to bring about more reduction in depression than low dosage tricyclics, although they cause more dropouts due to side effects than placebo (number needed to harm around 11).
Reaching definitive conclusions from these data, however, is not straightforward. The strength of our conclusions is compromised by several factors. Firstly, the quality of the included studies was not ideal. The success of blinding was not ascertained in any. Many studies did not employ operational diagnostic criteria and interview schedules to diagnose depression. Some studies used ad hoc outcome measures of unknown reliability and validity. Although the dropout rates were not high overall, as our worst case scenario intention to treat analyses showed, they were large enough to hamper drawing definitive conclusions. The dropout is always a problem but here it is even more prominent because, in the case of low dosage tricyclics, there is a trade-off between response and dropouts. If dropouts are not dealt with appropriately, the higher dosage always wins because it increases response at the expense of dropouts. Secondly, the quality of reporting in the included studies was not ideal. We are uncertain whether the random allocation was adequately concealed in most of the studies. Some studies failed to report standard deviations for their outcome measures. Thirdly, and perhaps due to the above factors, we noted heterogeneity for some of the pooled results. A few studies were extreme outliers, all in favour of the low dosage regimen. Lastly, most of the included studies lasted up to eight weeks only.
We evaluated the seriousness of these shortcomings with several sensitivity analyses. Omitting the positive small studies removed heterogeneity of the pooled analyses and yet showed little changes in relative risks and standardised mean differences. Limiting the studies to those that employed modern operational diagnostic criteria or those that used strictly low dosage regimens did not materially affect the pooled estimates of effect sizes.
These sensitivity analyses greatly strengthen the inferences that in
the treatment of depression tricyclics at dosages lower than the
usually recommended range are more effective than placebo but possibly
a little bit less effective than standard dosage tricyclics although
with fewer side effects. The evidence suggests that academicians have
been on weak ground in criticising clinicians' use of low dose
tricyclics. Every trial protocol should include strategies for ensuring
follow up of all the participants even if they stop the prescribed
drug, because it is the only way to adhere to the intention to treat
principle and to produce results permitting strong inferences about
treatment effects. Only then can the relative benefits and harms of
various dosages be definitively established.
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Acknowledgments |
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This systematic review was conducted within the framework of the Cochrane Collaboration Depression, Anxiety, and Neurosis Group. We thank Gordon Guyatt and David Streiner for their helpful comments on earlier drafts.
Contributors: TAF developed the idea of this systematic review and did the literature search, study selection, data extraction, and data analysis. HMcG did the literature search, study selection, and data extraction. CB did the study selection and helped in the interpretation of the results. All the investigators contributed to the writing of the paper and will act as guarantors.
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Footnotes |
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Funding: St Luke's Life Science Institute, Tokyo, Japan
provided 700 000 yen (£3659; $5696;
5835).
Competing interests: TAF has received fees for speaking from several pharmaceutical companies, some of which manufacture various types of antidepressants including paroxetine, fluroxamine, milnacipran.
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References |
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(Accepted 24 June 2002)
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