The Efficacy of Paxil (Paroxetine) for Panic Disorder Journal: The Current Practice of Medicine Authors: Dr Sean D. Hood, Dr Spilios Argyropoulos, Prof David J. Nutt Corresponding Author: Sean Hood ([email protected]) Introduction
Substantial advances into the pharmacological treatment of Panic Disorder (PD) have been made in the last
two decades. Although tricyclic antidepressants (TCADs), benzodiazepines and monoamine oxidase
inhibitors (MAOIs) have proven efficacy in this condition, their use is complicated by anticholinergic
effects, possible dependence, and dietary restrictions respectively. Specific serotonin reuptake inhibitors
(SSRIs) are increasingly used in PD and the current consensus is that pharmacotherapy should usually
begin with an SSRI [1, 2]. Paroxetine (Paxil), the first SSRI to obtain a licence for PD by the US Food &
Drug Administration, is generally well tolerated, safe, and has proven efficacy in treating conditions such
as depression and obsessive compulsive disorder (OCD). This article reviews the efficacy of Paroxetine in
Short Term Efficacy
A pivotal study of the efficacy of Paroxetine in PD, conducted by Oehrberg et al. in 1995 , was a
randomised, double-blind study of Paroxetine vs. Placebo with both groups receiving standardised
Cognitive & Behavioral Therapy (CBT). Seven centres in Denmark tested 120 DSM-IIIR defined PD +/-
Agoraphobia subjects in a flexible dose protocol (10 – 60 mg /day). Three weeks of single-blind placebo
preceded 12 weeks of double-blind treatment, and then two weeks of single-blind placebo. The principle
outcome measure was the frequency of panic attacks assessed using the Panic Inventory. Comparisons were
made using consecutive 3-week intervals. Table 1. Outcomes in Oehrberg et al. 1995 Result (p<0.05) Note: PAR=Paroxetine, P=Placebo, HAM-A=Hamilton Anxiety rating, CGI-S= Clinical Global
Paroxetine was well tolerated, with 92% completing the trial. In two of the three primary outcome variables
(viz: zero panic attacks and > 50% reduction in frequency of full panic atttacks) Paroxetine was
significantly more efficacious than placebo, and the average dose tested was 40-60 mg / day.
Meta-analyses of placebo-controlled double blind studies of TCAs support the view that Imipramine and
especially Clomipramine [4, 5] are efficacious in the short-term treatment of PD. So far there have been
few direct comparisons between TCADs and SSRIs in panic disorder. In a large (n=367) placebo controlled
study, Lecrubier et al.  compared Paroxetine with Clomipramine over a 12 week period. The majority
(80%) of patients had significant agoraphobic avoidance. After 3 weeks of single blind placebo washout
patients were randomly assigned to treatment groups. A flexible dosing regimen starting at 10 mg / day
minimised initial side effects whilst allowing clinically effective doses to be used. Most (70%) patients
remained in the trial until weeks 7-9. Table 2. Outcomes in Lecrubier et al. 1997 Result (p<0.05)
Improvement in Anxiety (HAM-A, CGI-S, PGE),
Agoraphobia (MSPS),Functional Disability (SDS).
High End-Stage (HES) respondersii (after )Note: PAR=Paroxetine, CLO=Clomipramine, P=Placebo, CNS=Central Nervous System,
GIT=Gastrointestinal, HAM-A=Hamilton Anxiety rating, CGI-S= Clinical Global Impression
Severity subscale, PGE=Patient’s Global Evaluation, MSPS=Modified Sad Person’s Score,
Despite a substantial placebo response (31.6% having none and 60% having at least a 50% reduction in
panic attacks by week 12), both Paroxetine and Clomipramine were significantly more effective than
placebo (see Table 2). Paroxetine had a faster onset than Clomipramine and was better tolerated. This
study offers powerful evidence that Paroxetine is at least as effective as Clomipramine in the acute
Until relatively recently, benzodiazepines were considered ineffective in the treatment of PD apart from a
circumscribed role in alleviating accompanying anticipatory anxiety. The anti-panic effects of the
i Trend: CLO (15%) > PAR (7%)ii Lydiard  has defined “High End-Stage” (HES) responders as those patients (LOCF, ITT) reporting zeropanic attacks and who were rated as having a CGI rating of 1 (very much improved) or 2 (much improved).
benzodiazepine Alprazolam has now been shown to be superior to placebo and at least as effective as
agents such as Imipramine . There are no ideal studies comparing Paroxetine and benzodiazepines
PAR 223 [See 7] was a randomised, double-blind, placebo-controlled, flexible-dose study of 226 patients
comparing placebo, Alprazolam (1-6 mg), and Paroxetine (10-60mg) over a 10 week period. This was a
“failed” trial in that the response rates to both Paroxetine (58.8%) and Alprazolam (62.0%) were similar to
that of placebo (62.7% with zero panic attacks). The average doses of active drug were modest – 26.3 mg
/day of Paroxetine and 2.8 mg / day of Alprazolam - which may have contributed to the inability to show a
A definitive dose finding study was conducted by Ballenger et al.  in a randomised, 10-week, placebo-
controlled design. Of 425 patients screened, 278 completed 2 weeks of single-blind placebo washout and
then were assigned to placebo or fixed dose 10, 20 or 40 mg /day Paroxetine. Primary outcome measures
were frequency of panic attacks (using Panic Inventory) and Clinical Global Improvement (CGI, a clinician
based rating). Patients were seen weekly for 4 weeks then every 2 weeks for the remainder of the study.
Analysis was conducted on ITT samples, 68% completed the 10-week trial. Table 3. Outcomes in Ballenger et al. 1998
Percentage free of full panic attacks.
Reduction in number of full panic attacks
High End-Stage (HES) responders ii (after )Note: Results where PAR (Paroxetine) was not significantly different to P (Placebo) are shown as
“-“. Doses are of Paroxetine. CGI-S = Severity subscale of Clinical Global Impression scale.
MSPS-F = Marks-Sheehan Phobia Scale-Fear subscale. MSPS-A = Marks-Sheehan Phobia
Scale-Avoidance subscale. MADRS= Montgomery-Åsberg Depression Rating Scale. HAM-A =
Hamilton Anxiety Rating Scale total score.
The 40 mg / day Paroxetine group had significantly greater improvement on 3 out of 4 primary outcome
measures and was superior to placebo on the majority of other measures. Side-effects were relatively few,
and there was no increase in drop-outs in the first two weeks due to increased anxiety or “jitteriness”. A
target dose of 40 mg was established as being effective and well tolerated. Long-Term Efficacy
As Panic disorder often runs a chronic course it is important to assess the long-term efficacy and
Participants who completed the comparative study of Paroxetine, Clomipramine and placebo (, above)
were invited to continue their double-blind treatment for a further 36 weeks . Of 176 patients
participating in this phase of the trial, 60 (34%) withdrew. Paroxetine withdrawal rates due to adverse
effects did not differ from placebo and withdrawal rates were highest for Clomipramine. Paroxetine (but
not Clomipramine) was significantly more effective than placebo throughout the study with respect to
reduction from baseline of full panic attacks, and at the end of treatment with respect to the proportion of
patients who eventually experienced no panic attacks.
Burnham et al  have examined relapse rates in 105 patients who responded to a 10-week double-blind
Paroxetine or Placebo trial by re-randomisation for a further 12 weeks. Paroxetine treated patients who
were then randomised to Placebo relapsed significantly more often (30%) than those who continued with
Paroxetine (5%). Side effects were similar to that seen in the first 10 weeks.
These studies confirm that Paroxetine continues to protect against relapse and is well tolerated in PD for up
Time to Response
The time to response to SSRIs in PD is often longer than that typically seen in the treatment of depressive
conditions. Paroxetine provides significant improvement in PD over the first 4  to 12 weeks of treatment
. Further improvement is sometimes seen with even longer treatment . Comparative Efficacy
There are no comparative studies between individual SSRIs in PD. The database for Paroxetine in PD is the
most extensive of the SSRIs although there is also good evidence of the efficacy of other SSRIs such as
Fluvoxamine and Citalopram. Choice of SSRI should also be guided by availability, clinician familiarity,
and broader considerations such as comorbidities and previous treatment history.
Comparison with TCAs and benzodiazepines has been made above. The quality of evidence for
anticonvulsants is limited. It is notable that β-blockers are ineffective treatments in panic disorder, despite
their frequent prescription for this condition by GP’s. Side Effects and Discontinuation
The side effect profile for Paroxetine in PD does not appear to differ markedly from that seen when it is
used to treat depression  and its tolerability in PD has been discussed above. The most common adverse
effects are nausea, headache, somnolence, dry mouth, insomnia, asthenia, sweating, and abnormal
ejaculation . Sexual side effects are dose related, and 21% of males with PD reporting abnormal
ejaculation and 5% impotence . The clinical practise of starting at 10 mg / day and gradually increasing
the dose, together with gradually reducing the dose over a few weeks is very effective at reducing side
effects and avoiding withdrawal reactions respectively. Fluvoxamine appears to be less likely than other
SSRI’s to cause ejaculatory retardation [13, 14] and thus is a useful alternative.
Discontinuation reactions may be more common with Paroxetine than other SSRI’s , especially when
ceasing abruptly from high doses. This is typically mild and begins 2 – 7 days after stopping treatment.
Typically gastrointestinal effects such as nausea, vomiting, and cramps are noted; vertigo, malaise,
muscular cramps and pseudo-influenza are also described [12, 16]. Comorbid Conditions
Comorbidity is usual in panic disorder, with major depressive episode, social anxiety disorder, other
anxiety disorders and alcohol dependence commonly seen. Paroxetine has proven efficacy in treating co-
morbid depressive symptomatology [6, 9, 10, 17], social anxiety disorder [12, 18] and Obsessive
Compulsive Disorder (OCD) [12, 19] which can minimise polyprescribing. Conclusions
Paroxetine has proven efficacy and tolerability in the treatment of Panic Disorder. It is at least as effective
as conventional treatments such as CBT, TCADs and benzodiazepines in short-term trials. A daily dose of
40 mg has been shown to be the most efficacious, however a graded titration to this dose will help to
minimise side effects. A clinical response is usually seen within 4 to 12 weeks, it continues to protect
against relapse for up to 12 months, and is an effective treatment of frequently co-morbid psychiatric
conditions. It is therefore a treatment of first choice in Panic Disorder. Declaration of Interest
One of the authors (SDH) is the recipient of a grant from SKB. Bibliography
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