Paxil
Generic Name: paroxetine hydrochloride
Dosage Form: Tablets, oral suspension
Suicidality in Children and Adolescents
Antidepressants
increased the risk of suicidal thinking and behavior (suicidality) in short-term
studies in children and adolescents with Major Depressive Disorder (MDD) and
other psychiatric disorders. Anyone considering the use of Paxil or any other
antidepressant in a child or adolescent must balance this risk with the clinical
need. Patients who are started on therapy should be observed closely for clinical
worsening, suicidality, or unusual changes in behavior. Families and caregivers
should be advised of the need for close observation and communication with
the prescriber. Paxil is not approved for use in pediatric patients. (See
WARNINGS and PRECAUTIONS—Pediatric
Use.)
Pooled analyses
of short-term (4 to 16 weeks) placebo-controlled trials of 9 antidepressant
drugs (SSRIs and others) in children and adolescents with major depressive
disorder (MDD), obsessive compulsive disorder (OCD), or other psychiatric
disorders (a total of 24 trials involving over 4,400 patients) have revealed
a greater risk of adverse events representing suicidal thinking or behavior
(suicidality) during the first few months of treatment in those receiving
antidepressants. The average risk of such events in patients receiving antidepressants
was 4%, twice the placebo risk of 2%. No suicides occurred in these trials.
Paxil Description
Paxil (paroxetine hydrochloride) is an orally administered
psychotropic drug. It is the hydrochloride salt of a phenylpiperidine compound
identified chemically as (-)-trans-4R-(4"-fluorophenyl)-3S-[(3",4"-methylenedioxyphenoxy) methyl] piperidine hydrochloride
hemihydrate and has the empirical formula of C19H20FNO3•HCl•1/2H2O.
The molecular weight is 374.8 (329.4 as free base). The structural formula
of paroxetine hydrochloride is:
Paroxetine hydrochloride is an odorless, off-white
powder, having a melting point range of 120° to 138°C and a solubility
of 5.4 mg/mL in water.
Tablets
Each film-coated tablet
contains paroxetine hydrochloride equivalent to paroxetine as follows: 10 mg−yellow
(scored); 20 mg−pink (scored); 30 mg−blue, 40 mg−green.
Inactive ingredients consist of dibasic calcium phosphate dihydrate, hypromellose,
magnesium stearate, polyethylene glycols, polysorbate 80, sodium starch glycolate,
titanium dioxide, and 1 or more of the following: D&C Red No. 30,
D&C Yellow No. 10, FD&C Blue No. 2, FD&C Yellow No. 6.
Suspension for Oral Administration
Each 5 mL of orange-colored,
orange-flavored liquid contains paroxetine hydrochloride equivalent to paroxetine,
10 mg. Inactive ingredients consist of polacrilin potassium, microcrystalline
cellulose, propylene glycol, glycerin, sorbitol, methyl paraben, propyl paraben,
sodium citrate dihydrate, citric acid anhydrate, sodium saccharin, flavorings,
FD&C Yellow No. 6, and simethicone emulsion, USP.
Paxil - Clinical Pharmacology
Pharmacodynamics
The efficacy of paroxetine in the treatment of major depressive
disorder, social anxiety disorder, obsessive compulsive disorder (OCD), panic
disorder (PD), generalized anxiety disorder (GAD), and posttraumatic stress
disorder (PTSD) is presumed to be linked to potentiation of serotonergic activity
in the central nervous system resulting from inhibition of neuronal reuptake
of serotonin (5-hydroxy-tryptamine, 5-HT). Studies at clinically relevant
doses in humans have demonstrated that paroxetine blocks the uptake of serotonin
into human platelets. In vitro studies in animals also suggest that paroxetine
is a potent and highly selective inhibitor of neuronal serotonin reuptake
and has only very weak effects on norepinephrine and dopamine neuronal reuptake.
In vitro radioligand binding studies indicate that paroxetine has little affinity
for muscarinic, alpha1-, alpha2-, beta-adrenergic-,
dopamine (D2)-, 5-HT1-, 5-HT2-, and histamine
(H1)-receptors; antagonism of muscarinic, histaminergic, and alpha1-adrenergic
receptors has been associated with various anticholinergic, sedative, and
cardiovascular effects for other psychotropic drugs.
Because
the relative potencies of paroxetine’s major metabolites are at most
1/50 of the parent compound, they are essentially inactive.
Pharmacokinetics
Paroxetine hydrochloride is completely absorbed after oral
dosing of a solution of the hydrochloride salt. The mean elimination half-life
is approximately 21 hours (CV 32%) after oral dosing of 30 mg
tablets of Paxil daily for 30 days. Paroxetine is extensively metabolized
and the metabolites are considered to be inactive. Nonlinearity in pharmacokinetics
is observed with increasing doses. Paroxetine metabolism is mediated in part
by CYP2D6, and the metabolites are primarily excreted in the urine and to
some extent in the feces. Pharmacokinetic behavior of paroxetine has not been
evaluated in subjects who are deficient in CYP2D6 (poor metabolizers).
Absorption and Distribution
Paroxetine is equally bioavailable from the oral suspension
and tablet.
Paroxetine hydrochloride is completely
absorbed after oral dosing of a solution of the hydrochloride salt. In a study
in which normal male subjects (n = 15) received 30 mg tablets
daily for 30 days, steady-state paroxetine concentrations were achieved
by approximately 10 days for most subjects, although it may take substantially
longer in an occasional patient. At steady state, mean values of Cmax,
Tmax,Cmin, and T½ were 61.7 ng/mL
(CV 45%), 5.2 hr. (CV 10%), 30.7 ng/mL (CV 67%),
and 21.0 hours (CV 32%), respectively. The steady-state Cmax and
Cmin values were about 6 and 14 times what would be predicted from
single-dose studies. Steady-state drug exposure based on AUC0-24 was
about 8 times greater than would have been predicted from single-dose data
in these subjects. The excess accumulation is a consequence of the fact that
1 of the enzymes that metabolizes paroxetine is readily saturable.
The
effects of food on the bioavailability of paroxetine were studied in subjects
administered a single dose with and without food. AUC was only slightly increased
(6%) when drug was administered with food but the Cmax was 29%
greater, while the time to reach peak plasma concentration decreased from
6.4 hours post-dosing to 4.9 hours.
Paroxetine
distributes throughout the body, including the CNS, with only 1% remaining
in the plasma.
Approximately 95% and 93% of paroxetine
is bound to plasma protein at 100 ng/mL and 400 ng/mL, respectively.
Under clinical conditions, paroxetine concentrations would normally be less
than 400 ng/mL. Paroxetine does not alter the in vitro protein binding
of phenytoin or warfarin.
Metabolism and Excretion
The mean elimination half-life is approximately 21 hours
(CV 32%) after oral dosing of 30 mg tablets daily for 30 days
of Paxil. In steady-state dose proportionality studies involving elderly and
nonelderly patients, at doses of 20 mg to 40 mg daily for the elderly
and 20 mg to 50 mg daily for the nonelderly, some nonlinearity was
observed in both populations, again reflecting a saturable metabolic pathway.
In comparison to Cmin values after 20 mg daily, values after
40 mg daily were only about 2 to 3 times greater than doubled.
Paroxetine
is extensively metabolized after oral administration. The principal metabolites
are polar and conjugated products of oxidation and methylation, which are
readily cleared. Conjugates with glucuronic acid and sulfate predominate,
and major metabolites have been isolated and identified. Data indicate that
the metabolites have no more than 1/50 the potency of the parent compound
at inhibiting serotonin uptake. The metabolism of paroxetine is accomplished
in part by CYP2D6. Saturation of this enzyme at clinical doses appears to
account for the nonlinearity of paroxetine kinetics with increasing dose and
increasing duration of treatment. The role of this enzyme in paroxetine metabolism
also suggests potential drug-drug interactions (see PRECAUTIONS).
Approximately
64% of a 30-mg oral solution dose of paroxetine was excreted in the urine
with 2% as the parent compound and 62% as metabolites over a 10-day post-dosing
period. About 36% was excreted in the feces (probably via the bile), mostly
as metabolites and less than 1% as the parent compound over the 10-day post-dosing
period.
Other Clinical Pharmacology Information
Specific Populations
Renal and Liver Disease
Increased plasma concentrations of paroxetine occur in subjects
with renal and hepatic impairment. The mean plasma concentrations in patients
with creatinine clearance below 30 mL/min. was approximately 4 times
greater than seen in normal volunteers. Patients with creatinine clearance
of 30 to 60 mL/min. and patients with hepatic functional impairment had
about a 2-fold increase in plasma concentrations (AUC, Cmax).
The
initial dosage should therefore be reduced in patients with severe renal or
hepatic impairment, and upward titration, if necessary, should be at increased
intervals (see DOSAGE AND ADMINISTRATION).
Elderly Patients
In a multiple-dose study in the elderly at daily paroxetine
doses of 20, 30, and 40 mg, Cmin concentrations were about
70% to 80% greater than the respective Cmin concentrations in nonelderly
subjects. Therefore the initial dosage in the elderly should be reduced (see
DOSAGE AND ADMINISTRATION).
Drug-Drug Interactions
In vitro drug interaction studies reveal that paroxetine
inhibits CYP2D6. Clinical drug interaction studies have been performed with
substrates of CYP2D6 and show that paroxetine can inhibit the metabolism of
drugs metabolized by CYP2D6 including desipramine, risperidone, and atomoxetine
(see PRECAUTIONS—Drug Interactions).
Clinical Trials
Major Depressive Disorder
The efficacy of Paxil
as a treatment for major depressive disorder has been established in 6 placebo-controlled
studies of patients with major depressive disorder (aged 18 to 73). In these
studies, Paxil was shown to be significantly more effective than placebo in
treating major depressive disorder by at least 2 of the following measures:
Hamilton Depression Rating Scale (HDRS), the Hamilton depressed mood item,
and the Clinical Global Impression (CGI)-Severity of Illness. Paxil was significantly
better than placebo in improvement of the HDRS sub-factor scores, including
the depressed mood item, sleep disturbance factor, and anxiety factor.
A
study of outpatients with major depressive disorder who had responded to Paxil
(HDRS total score <8) during an initial 8-week open-treatment phase and
were then randomized to continuation on Paxil or placebo for 1 year demonstrated
a significantly lower relapse rate for patients taking Paxil (15%) compared
to those on placebo (39%). Effectiveness was similar for male and female patients.
Obsessive Compulsive Disorder
The effectiveness of
Paxil in the treatment of obsessive compulsive disorder (OCD) was demonstrated
in two 12-week multicenter placebo-controlled studies of adult outpatients
(Studies 1 and 2). Patients in all studies had moderate to severe OCD (DSM-IIIR)
with mean baseline ratings on the Yale Brown Obsessive Compulsive Scale (YBOCS)
total score ranging from 23 to 26. Study 1, a dose-range finding study where
patients were treated with fixed doses of 20, 40, or 60 mg of paroxetine/day
demonstrated that daily doses of paroxetine 40 and 60 mg are effective
in the treatment of OCD. Patients receiving doses of 40 and 60 mg paroxetine
experienced a mean reduction of approximately 6 and 7 points, respectively,
on the YBOCS total score which was significantly greater than the approximate
4-point reduction at 20 mg and a 3-point reduction in the placebo-treated
patients. Study 2 was a flexible-dose study comparing paroxetine (20 to 60 mg
daily) with clomipramine (25 to 250 mg daily). In this study, patients
receiving paroxetine experienced a mean reduction of approximately 7 points
on the YBOCS total score, which was significantly greater than the mean reduction
of approximately 4 points in placebo-treated patients.
The
following table provides the outcome classification by treatment group on
Global Improvement items of the Clinical Global Impression (CGI) scale for
Study 1.
Outcome
Classification (%) on CGI-Global Improvement Item |
for
Completers in Study 1 |
Outcome
Classification |
Placebo
(n = 74) |
Paxil
20 mg (n = 75) |
Paxil
40 mg (n = 66) |
Paxil
60 mg (n = 66) |
|
|
|
|
|
Worse |
14% |
7% |
7% |
3% |
No Change |
44% |
35% |
22% |
19% |
Minimally Improved |
24% |
33% |
29% |
34% |
Much Improved |
11% |
18% |
22% |
24% |
Very Much Improved |
7% |
7% |
20% |
20% |
Subgroup analyses did not indicate that there were any
differences in treatment outcomes as a function of age or gender.
The
long-term maintenance effects of Paxil in OCD were demonstrated in a long-term
extension to Study 1. Patients who were responders on paroxetine during the
3-month double-blind phase and a 6-month extension on open-label paroxetine
(20 to 60 mg/day) were randomized to either paroxetine or placebo in
a 6-month double-blind relapse prevention phase. Patients randomized to paroxetine
were significantly less likely to relapse than comparably treated patients
who were randomized to placebo.
Panic Disorder
The effectiveness of
Paxil in the treatment of panic disorder was demonstrated in three 10- to
12-week multicenter, placebo-controlled studies of adult outpatients (Studies
1-3). Patients in all studies had panic disorder (DSM-IIIR), with or without
agoraphobia. In these studies, Paxil was shown to be significantly more effective
than placebo in treating panic disorder by at least 2 out of 3 measures of
panic attack frequency and on the Clinical Global Impression Severity of Illness
score.
Study 1 was a 10-week dose-range finding study;
patients were treated with fixed paroxetine doses of 10, 20, or 40 mg/day
or placebo. A significant difference from placebo was observed only for the
40 mg/day group. At endpoint, 76% of patients receiving paroxetine 40 mg/day
were free of panic attacks, compared to 44% of placebo-treated patients.
Study
2 was a 12-week flexible-dose study comparing paroxetine (10 to 60 mg
daily) and placebo. At endpoint, 51% of paroxetine patients were free of panic
attacks compared to 32% of placebo-treated patients.
Study
3 was a 12-week flexible-dose study comparing paroxetine (10 to 60 mg
daily) to placebo in patients concurrently receiving standardized cognitive
behavioral therapy. At endpoint, 33% of the paroxetine-treated patients showed
a reduction to 0 or 1 panic attacks compared to 14% of placebo patients.
In
both Studies 2 and 3, the mean paroxetine dose for completers at endpoint
was approximately 40 mg/day of paroxetine.
Long-term
maintenance effects of Paxil in panic disorder were demonstrated in an extension
to Study 1. Patients who were responders during the 10-week double-blind phase
and during a 3-month double-blind extension phase were randomized to either
paroxetine (10, 20, or 40 mg/day) or placebo in a 3-month double-blind
relapse prevention phase. Patients randomized to paroxetine were significantly
less likely to relapse than comparably treated patients who were randomized
to placebo.
Subgroup analyses did not indicate that
there were any differences in treatment outcomes as a function of age or gender.
Social Anxiety Disorder
The effectiveness of
Paxil in the treatment of social anxiety disorder was demonstrated in three
12-week, multicenter, placebo-controlled studies (Studies 1, 2, and 3) of
adult outpatients with social anxiety disorder (DSM-IV). In these studies,
the effectiveness of Paxil compared to placebo was evaluated on the basis
of (1) the proportion of responders, as defined by a Clinical Global Impression
(CGI) Improvement score of 1 (very much improved) or 2 (much improved), and
(2) change from baseline in the Liebowitz Social Anxiety Scale (LSAS).
Studies
1 and 2 were flexible-dose studies comparing paroxetine (20 to 50 mg
daily) and placebo. Paroxetine demonstrated statistically significant superiority
over placebo on both the CGI Improvement responder criterion and the Liebowitz
Social Anxiety Scale (LSAS). In Study 1, for patients who completed to
week 12, 69% of paroxetine-treated patients compared to 29% of placebo-treated
patients were CGI Improvement responders. In Study 2, CGI Improvement responders
were 77% and 42% for the paroxetine- and placebo-treated patients, respectively.
Study
3 was a 12-week study comparing fixed paroxetine doses of 20, 40, or 60 mg/day
with placebo. Paroxetine 20 mg was demonstrated to be significantly superior
to placebo on both the LSAS Total Score and the CGI Improvement responder
criterion; there were trends for superiority over placebo for the 40 mg
and 60 mg/day dose groups. There was no indication in this study of any
additional benefit for doses higher than 20 mg/day.
Subgroup
analyses generally did not indicate differences in treatment outcomes as a
function of age, race, or gender.
Generalized Anxiety Disorder
The effectiveness of
Paxilin the treatment of Generalized
Anxiety Disorder (GAD) was demonstrated in two 8-week, multicenter, placebo-controlled
studies (Studies 1 and 2) of adult outpatients with Generalized Anxiety Disorder
(DSM-IV).
Study 1 was an 8-week study comparing fixed
paroxetine doses of 20 mg or 40 mg/day with placebo. Doses of 20 mg
or 40 mg of Paxil were both demonstrated to be significantly superior
to placebo on the Hamilton Rating Scale for Anxiety (HAM-A) total score. There
was not sufficient evidence in this study to suggest a greater benefit for
the 40 mg/day dose compared to the 20 mg/day dose.
Study 2
was a flexible-dose study comparing paroxetine (20 mg to 50 mg daily)
and placebo. Paxil demonstrated statistically significant superiority over
placebo on the Hamilton Rating Scale for Anxiety (HAM-A) total score. A third
study, also flexible-dose comparing paroxetine (20 mg to 50 mg daily),
did not demonstrate statistically significant superiority of Paxil over placebo
on the Hamilton Rating Scale for Anxiety (HAM-A) total score, the primary
outcome.
Subgroup analyses did not indicate differences
in treatment outcomes as a function of race or gender. There were insufficient
elderly patients to conduct subgroup analyses on the basis of age.
In
a longer-term trial, 566 patients meeting DSM-IV criteria for Generalized
Anxiety Disorder, who had responded during a single-blind, 8-week acute treatment
phase with 20 to 50 mg/day of Paxil, were randomized to continuation
of Paxil at their same dose, or to placebo, for up to 24 weeks of observation
for relapse. Response during the single-blind phase was defined by having
a decrease of ≥2 points compared to baseline on the CGI-Severity of
Illness scale, to a score of ≤3. Relapse during the double-blind phase
was defined as an increase of ≥2 points compared to baseline on the
CGI-Severity of Illness scale to a score of ≥4, or withdrawal due to
lack of efficacy. Patients receiving continued Paxil experienced a significantly
lower relapse rate over the subsequent 24 weeks compared to those receiving
placebo.
Posttraumatic Stress Disorder
The effectiveness of
Paxil in the treatment of Posttraumatic Stress Disorder (PTSD) was demonstrated
in two 12-week, multicenter, placebo-controlled studies (Studies 1 and 2)
of adult outpatients who met DSM-IV criteria for PTSD. The mean duration of
PTSD symptoms for the 2 studies combined was 13 years (ranging from .1
year to 57 years). The percentage of patients with secondary major depressive
disorder or non-PTSD anxiety disorders in the combined 2 studies was 41% (356
out of 858 patients) and 40% (345 out of 858 patients), respectively. Study
outcome was assessed by (i) the Clinician-Administered PTSD Scale Part 2 (CAPS-2)
score and (ii) the Clinical Global Impression-Global Improvement Scale (CGI-I).
The CAPS-2 is a multi-item instrument that measures 3 aspects of PTSD with
the following symptom clusters: Reexperiencing/intrusion, avoidance/numbing
and hyperarousal. The 2 primary outcomes for each trial were (i) change from
baseline to endpoint on the CAPS-2 total score (17 items), and (ii) proportion
of responders on the CGI-I, where responders were defined as patients having
a score of 1 (very much improved) or 2 (much improved).
Study
1 was a 12-week study comparing fixed paroxetine doses of 20 mg or 40 mg/day
to placebo. Doses of 20 mg and 40 mg of Paxil were demonstrated
to be significantly superior to placebo on change from baseline for the CAPS-2
total score and on proportion of responders on the CGI-I. There was not sufficient
evidence in this study to suggest a greater benefit for the 40 mg/day
dose compared to the 20 mg/day dose.
Study 2 was
a 12-week flexible-dose study comparing paroxetine (20 to 50 mg daily)
to placebo. Paxil was demonstrated to be significantly superior to placebo
on change from baseline for the CAPS-2 total score and on proportion of responders
on the CGI-I.
A third study, also a flexible-dose study
comparing paroxetine (20 to 50 mg daily) to placebo, demonstrated Paxil
to be significantly superior to placebo on change from baseline for CAPS-2
total score, but not on proportion of responders on the CGI-I.
The
majority of patients in these trials were women (68% women: 377 out of 551
subjects in Study 1 and 66% women: 202 out of 303 subjects in Study 2). Subgroup
analyses did not indicate differences in treatment outcomes as a function
of gender. There were an insufficient number of patients who were 65 years
and older or were non-Caucasian to conduct subgroup analyses on the basis
of age or race, respectively.
Indications and Usage for Paxil
Major Depressive Disorder
Paxil is indicated for
the treatment of major depressive disorder.
The efficacy
of Paxilin the treatment of a major
depressive episode was established in 6-week controlled trials of outpatients
whose diagnoses corresponded most closely to the DSM-III category of major
depressive disorder (see CLINICAL PHARMACOLOGY—Clinical Trials). A
major depressive episode implies a prominent and relatively persistent depressed
or dysphoric mood that usually interferes with daily functioning (nearly every
day for at least 2 weeks); it should include at least 4 of the following
8 symptoms: Change in appetite, change in sleep, psychomotor agitation
or retardation, loss of interest in usual activities or decrease in sexual
drive, increased fatigue, feelings of guilt or worthlessness, slowed thinking
or impaired concentration, and a suicide attempt or suicidal ideation.
The
effects of Paxil in hospitalized depressed patients have not been adequately
studied.
The efficacy of Paxil in maintaining a response
in major depressive disorder for up to 1 year was demonstrated in a placebo-controlled
trial (see CLINICAL PHARMACOLOGY—Clinical Trials). Nevertheless, the
physician who elects to use Paxil for extended periods should periodically
re-evaluate the long-term usefulness of the drug for the individual patient.
Obsessive Compulsive Disorder
Paxil is indicated for
the treatment of obsessions and compulsions in patients with obsessive compulsive
disorder (OCD) as defined in the DSM-IV. The obsessions or compulsions cause
marked distress, are time-consuming, or significantly interfere with social
or occupational functioning.
The efficacy of Paxil
was established in two 12-week trials with obsessive compulsive outpatients
whose diagnoses corresponded most closely to the DSM-IIIR category of obsessive
compulsive disorder (see CLINICAL PHARMACOLOGY—Clinical Trials).
Obsessive
compulsive disorder is characterized by recurrent and persistent ideas, thoughts,
impulses, or images (obsessions) that are ego-dystonic and/or repetitive,
purposeful, and intentional behaviors (compulsions) that are recognized by
the person as excessive or unreasonable.
Long-term
maintenance of efficacy was demonstrated in a 6-month relapse prevention trial.
In this trial, patients assigned to paroxetine showed a lower relapse rate
compared to patients on placebo (see CLINICAL PHARMACOLOGY—Clinical
Trials). Nevertheless, the physician who elects to use Paxilfor extended periods should periodically re-evaluate the long-term
usefulness of the drug for the individual patient (see DOSAGE AND ADMINISTRATION).
Panic Disorder
Paxil is indicated for
the treatment of panic disorder, with or without agoraphobia, as defined in
DSM-IV. Panic disorder is characterized by the occurrence of unexpected panic
attacks and associated concern about having additional attacks, worry about
the implications or consequences of the attacks, and/or a significant change
in behavior related to the attacks.
The efficacy of
Paxil was established in three 10- to 12-week trials in panic disorder patients
whose diagnoses corresponded to the DSM-IIIR category of panic disorder (see
CLINICAL PHARMACOLOGY—Clinical Trials).
Panic
disorder (DSM-IV) is characterized by recurrent unexpected panic attacks,
i.e., a discrete period of intense fear or discomfort in which 4 (or more)
of the following symptoms develop abruptly and reach a peak within 10 minutes:
(1) palpitations, pounding heart, or accelerated heart rate; (2) sweating;
(3) trembling or shaking; (4) sensations of shortness of breath or smothering;
(5) feeling of choking; (6) chest pain or discomfort; (7) nausea or abdominal
distress; (8) feeling dizzy, unsteady, lightheaded, or faint; (9) derealization
(feelings of unreality) or depersonalization (being detached from oneself);
(10) fear of losing control; (11) fear of dying; (12) paresthesias (numbness
or tingling sensations); (13) chills or hot flushes.
Long-term
maintenance of efficacy was demonstrated in a 3-month relapse prevention trial.
In this trial, patients with panic disorder assigned to paroxetine demonstrated
a lower relapse rate compared to patients on placebo (see CLINICAL PHARMACOLOGY—Clinical
Trials). Nevertheless, the physician who prescribes Paxil for extended periods
should periodically re-evaluate the long-term usefulness of the drug for the
individual patient.
Social Anxiety Disorder
Paxil is indicated for
the treatment of social anxiety disorder, also known as social phobia, as
defined in DSM-IV (300.23). Social anxiety disorder is characterized by a
marked and persistent fear of 1 or more social or performance situations in
which the person is exposed to unfamiliar people or to possible scrutiny by
others. Exposure to the feared situation almost invariably provokes anxiety,
which may approach the intensity of a panic attack. The feared situations
are avoided or endured with intense anxiety or distress. The avoidance, anxious
anticipation, or distress in the feared situation(s) interferes significantly
with the person"s normal routine, occupational or academic functioning, or
social activities or relationships, or there is marked distress about having
the phobias. Lesser degrees of performance anxiety or shyness generally do
not require psychopharmacological treatment.
The efficacy
of Paxil was established in three 12-week trials in adult patients with social
anxiety disorder (DSM-IV). Paxil has not been studied in children or adolescents
with social phobia (see CLINICAL PHARMACOLOGY—Clinical Trials).
The
effectiveness of Paxil in long-term treatment of social anxiety disorder,
i.e., for more than 12 weeks, has not been systematically evaluated in
adequate and well-controlled trials. Therefore, the physician who elects to
prescribe Paxil for extended periods should periodically re-evaluate the long-term
usefulness of the drug for the individual patient (see DOSAGE AND ADMINISTRATION).
Generalized Anxiety Disorder
Paxil is indicated for
the treatment of Generalized Anxiety Disorder (GAD), as defined in DSM-IV.
Anxiety or tension associated with the stress of everyday life usually does
not require treatment with an anxiolytic.
The efficacy
of Paxil in the treatment of GAD was established in two 8-week placebo-controlled
trials in adults with GAD. Paxil has not been studied in children or adolescents
with Generalized Anxiety Disorder (see CLINICAL PHARMACOLOGY—Clinical
Trials).
Generalized Anxiety Disorder (DSM-IV) is
characterized by excessive anxiety and worry (apprehensive expectation) that
is persistent for at least 6 months and which the person finds difficult
to control. It must be associated with at least 3 of the following 6 symptoms:
Restlessness or feeling keyed up or on edge, being easily fatigued, difficulty
concentrating or mind going blank, irritability, muscle tension, sleep disturbance.
The
efficacy of Paxil in maintaining a response in patients with Generalized Anxiety
Disorder, who responded during an 8-week acute treatment phase while taking
Paxil and were then observed for relapse during a period of up to 24 weeks,
was demonstrated in a placebo-controlled trial (see CLINICAL PHARMACOLOGY—Clinical
Trials). Nevertheless, the physician who elects to use Paxil for extended
periods should periodically re-evaluate the long-term usefulness of the drug
for the individual patient (see DOSAGE AND ADMINISTRATION).
Posttraumatic Stress Disorder
Paxil is indicated for
the treatment of Posttraumatic Stress Disorder (PTSD).
The
efficacy of Paxil in the treatment of PTSD was established in two 12-week
placebo-controlled trials in adults with PTSD (DSM-IV) (see CLINICAL PHARMACOLOGY—Clinical
Trials).
PTSD, as defined by DSM-IV, requires exposure
to a traumatic event that involved actual or threatened death or serious injury,
or threat to the physical integrity of self or others, and a response that
involves intense fear, helplessness, or horror. Symptoms that occur as a result
of exposure to the traumatic event include reexperiencing of the event in
the form of intrusive thoughts, flashbacks, or dreams, and intense psychological
distress and physiological reactivity on exposure to cues to the event; avoidance
of situations reminiscent of the traumatic event, inability to recall details
of the event, and/or numbing of general responsiveness manifested as diminished
interest in significant activities, estrangement from others, restricted range
of affect, or sense of foreshortened future; and symptoms of autonomic arousal
including hypervigilance, exaggerated startle response, sleep disturbance,
impaired concentration, and irritability or outbursts of anger. A PTSD diagnosis
requires that the symptoms are present for at least a month and that they
cause clinically significant distress or impairment in social, occupational,
or other important areas of functioning.
The efficacy
of Paxil in longer-term treatment of PTSD, i.e., for more than 12 weeks, has
not been systematically evaluated in placebo-controlled trials. Therefore,
the physician who elects to prescribe Paxil for extended periods should periodically
re-evaluate the long-term usefulness of the drug for the individual patient
(see DOSAGE AND ADMINISTRATION).
Contraindications
Concomitant use in patients taking either monoamine oxidase
inhibitors (MAOIs) or thioridazine is contraindicated (see WARNINGS and PRECAUTIONS).
Concomitant
use in patients taking pimozide is contraindicated (see PRECAUTIONS).
Paxil
is contraindicated in patients with a hypersensitivity to paroxetine or any
of the inactive ingredients in Paxil.
Warnings
Clinical Worsening and Suicide Risk
Patients with major depressive disorder (MDD), both adult
and pediatric, may experience worsening of their depression and/or the emergence
of suicidal ideation and behavior (suicidality) or unusual changes in behavior,
whether or not they are taking antidepressant medications, and this risk may
persist until significant remission occurs. There has been a long-standing
concern that antidepressants may have a role in inducing worsening of depression
and the emergence of suicidality in certain patients. Antidepressants increased
the risk of suicidal thinking and behavior (suicidality) in short-term studies
in children and adolescents with Major Depressive Disorder (MDD) and other
psychiatric disorders.
Pooled analyses of short-term
placebo-controlled trials of 9 antidepressant drugs (SSRIs and others)
in children and adolescents with MDD, OCD, or other psychiatric disorders
(a total of 24 trials involving over 4,400 patients) have revealeda greater risk of adverse events representing suicidal behavior or thinking
(suicidality) during the first few months of treatment in those receiving
antidepressants. The average risk of such events in patients receiving antidepressants
was 4%, twice the placebo risk of 2%. There was considerable variation in
risk among drugs, but a tendency toward an increase for almost all drugs studied.
The risk of suicidality was most consistently observed in the MDD trials,
but there were signals of risk arising from some trials in other psychiatric
indications (obsessive compulsive disorder and social anxiety disorder) as
well. No suicides occurred in any of these trials. It is unknown whether the suicidality risk in pediatric patients
extends to longer-term use, i.e., beyond several months. It is also unknown
whether the suicidality risk extends to adults.
All pediatric patients being treated with antidepressants
for any indication should be observed closely for clinical worsening, suicidality,
and unusual changes in behavior, especially during the initial few months
of a course of drug therapy, or at times of dose changes, either increases
or decreases. Such observation would generally include at least weekly face-to-face
contact with patients or their family members or caregivers during the first
4 weeks of treatment, then every other week visits for the next 4 weeks,
then at 12 weeks, and as clinically indicated beyond 12 weeks. Additional
contact by telephone may be appropriate between face-to-face visits.
Adults with MDD or co-morbid depression in the setting of
other psychiatric illness being treated with antidepressants should be observed
similarly for clinical worsening and suicidality, especially during the initial
few months of a course of drug therapy, or at times of dose changes, either
increases or decreases.
In
addition, patients with a history of suicidal behavior or thoughts, those
patients exhibiting a significant degree of suicidal ideation prior to commencement
of treatment, and young adults, are at an increased risk of suicidal thoughts
or suicide attempts, and should receive careful monitoring during treatment.
The following symptoms, anxiety, agitation,
panic attacks, insomnia, irritability, hostility, aggressiveness, impulsivity,
akathisia (psychomotor restlessness), hypomania, and mania, have been reported
in adult and pediatric patients being treated with antidepressants for major
depressive disorder as well as for other indications, both psychiatric and
nonpsychiatric. Although a causal link between the emergence of such symptoms
and either the worsening of depression and/or the emergence of suicidal impulses
has not been established, there is concern that such symptoms may represent
precursors to emerging suicidality.
Consideration should
be given to changing the therapeutic regimen, including possibly discontinuing
the medication, in patients whose depression is persistently worse, or who
are experiencing emergent suicidality or symptoms that might be precursors
to worsening depression or suicidality, especially if these symptoms are severe,
abrupt in onset, or were not part of the patient’s presenting symptoms.
If
the decision has been made to discontinue treatment, medication should be
tapered, as rapidly as is feasible, but with recognition that abrupt discontinuation
can be associated with certain symptoms (see PRECAUTIONS and DOSAGE AND ADMINISTRATION—Discontinuation
of Treatment With Paxil, for a description of the risks of discontinuation
of Paxil).
Families and caregivers
of pediatric patients being treated with antidepressants for major depressive
disorder or other indications, both psychiatric and nonpsychiatric, should
be alerted about the need to monitor patients for the emergence of agitation,
irritability, unusual changes in behavior, and the other symptoms described
above, as well as the emergence of suicidality, and to report such symptoms
immediately to health care providers.Such
monitoring should include daily observation by families and caregivers. Prescriptions
for Paxil should be written for the smallest quantity of tablets consistent
with good patient management, in order to reduce the risk of overdose. Families
and caregivers of adults being treated for depression should be similarly
advised.
Screening Patients for Bipolar Disorder
A major depressive episode
may be the initial presentation of bipolar disorder. It is generally believed
(though not established in controlled trials) that treating such an episode
with an antidepressant alone may increase the likelihood of precipitation
of a mixed/manic episode in patients at risk for bipolar disorder. Whether
any of the symptoms described above represent such a conversion is unknown.
However, prior to initiating treatment with an antidepressant, patients with
depressive symptoms should be adequately screened to determine if they are
at risk for bipolar disorder; such screening should include a detailed psychiatric
history, including a family history of suicide, bipolar disorder, and depression.
It should be noted that Paxil is not approved for use in treating bipolar
depression.
Potential for Interaction With Monoamine Oxidase Inhibitors
In patients receiving another
serotonin reuptake inhibitor drug in combination with a monoamine oxidase
inhibitor (MAOI), there have been reports of serious, sometimes fatal, reactions
including hyperthermia, rigidity, myoclonus, autonomic instability with possible
rapid fluctuations of vital signs, and mental status changes that include
extreme agitation progressing to delirium and coma. These reactions have also
been reported in patients who have recently discontinued that drug and have
been started on an MAOI. Some cases presented with features resembling neuroleptic
malignant syndrome. While there are no human data showing such an interaction
with Paxil, limited animal data on the effects of combined use of paroxetine
and MAOIs suggest that these drugs may act synergistically to elevate blood
pressure and evoke behavioral excitation. Therefore, it is recommended that
Paxil not be used in combination with an MAOI, or within 14 days of discontinuing
treatment with an MAOI. At least 2 weeks should be allowed after stopping
Paxil before starting an MAOI.
Potential Interaction With Thioridazine
Thioridazine administration alone
produces prolongation of the QTc interval, which is associated with serious
ventricular arrhythmias, such as torsade de pointes−type arrhythmias, and sudden death. This effect appears to
be dose related.
An
in vivo study suggests that drugs which inhibit CYP2D6, such as paroxetine,
will elevate plasma levels of thioridazine. Therefore, it is recommended that
paroxetine not be used in combination with thioridazine (see CONTRAINDICATIONS
and PRECAUTIONS).
Usage in Pregnancy
Teratogenic Effects
Epidemiological studies have shown that infants born to
women who had first trimester paroxetine exposure had an increased risk of
cardiovascular malformations, primarily ventricular and atrial septal defects
(VSDs and ASDs). In general, septal defects range from those that are symptomatic
and may require surgery to those that are asymptomatic and may resolve spontaneously.
If a patient becomes pregnant while taking paroxetine, she should be advised
of the potential harm to the fetus. Unless the benefits of paroxetine to the
mother justify continuing treatment, consideration should be given to either
discontinuing paroxetine therapy or switching to another antidepressant (see
PRECAUTIONS—Discontinuation of Treatment with Paxil). For women who intend to become pregnant or are in their first
trimester of pregnancy, paroxetine should only be initiated after consideration
of the other available treatment options.
A study based
on Swedish national registry data evaluated infants of 6,896 women exposed
to antidepressants in early pregnancy (5,123 women exposed to SSRIs; including
815 for paroxetine). Infants exposed to paroxetine in early pregnancy had
an increased risk of cardiovascular malformations (primarily VSDs and ASDs)
compared to the entire registry population (OR 1.8; 95% confidence interval
1.1-2.8). The rate of cardiovascular malformations following early pregnancy
paroxetine exposure was 2% vs. 1% in the entire registry population. Among
the same paroxetine exposed infants, an examination of the data showed no
increase in the overall risk for congenital malformations.
A
separate retrospective cohort study using US United Healthcare data evaluated
5,956 infants of mothers dispensed paroxetine or other antidepressants during
the first trimester (n = 815 for paroxetine). This study showed
a trend towards an increased risk for cardiovascular malformations for paroxetine
compared to other antidepressants (OR 1.5; 95% confidence interval 0.8-2.9).
The prevalence of cardiovascular malformations following first trimester dispensing
was 1.5% for paroxetine vs. 1% for other antidepressants. Nine out of 12 infants
with cardiovascular malformations whose mothers were dispensed paroxetine
in the first trimester had VSDs. This study also suggested an increased risk
of overall major congenital malformations (inclusive of the cardiovascular
defects) for paroxetine compared to other antidepressants (OR 1.8; 95% confidence
interval 1.2-2.8). The prevalence of all congenital malformations following
first trimester exposure was 4% for paroxetine vs. 2% for other antidepressants.
Animal Findings
Reproduction studies were performed at doses up to 50 mg/kg/day
in rats and 6 mg/kg/day in rabbits administered during organogenesis.
These doses are approximately 8 (rat) and 2 (rabbit) times the MRHD
on an mg/m2 basis. These studies have revealed no evidence of teratogenic
effects. However, in rats, there was an increase in pup deaths during the
first 4 days of lactation when dosing occurred during the last trimester
of gestation and continued throughout lactation. This effect occurred at a
dose of 1 mg/kg/day or approximately one-sixth of the MRHD on an mg/m2 basis.
The no-effect dose for rat pup mortality was not determined. The cause of
these deaths is not known.
Nonteratogenic Effects
Neonates exposed to Paxil
and other SSRIs or serotonin and norepinephrine reuptake inhibitors (SNRIs),
late in the third trimester have developed complications requiring prolonged
hospitalization, respiratory support, and tube feeding. Such complications
can arise immediately upon delivery. Reported clinical findings have included
respiratory distress, cyanosis, apnea, seizures, temperature instability,
feeding difficulty, vomiting, hypoglycemia, hypotonia, hypertonia, hyperreflexia,
tremor, jitteriness, irritability, and constant crying. These features are
consistent with either a direct toxic effect of SSRIs and SNRIs or, possibly,
a drug discontinuation syndrome. It should be noted that, in some cases, the
clinical picture is consistent with serotonin syndrome (see WARNINGS—Potential
for Interaction With Monoamine Oxidase Inhibitors).
There
have also been postmarketing reports of premature births in pregnant women
exposed to paroxetine or other SSRIs.
When treating
a pregnant woman with paroxetine during the third trimester, the physician
should carefully consider the potential risks and benefits of treatment (see
DOSAGE AND ADMINISTRATION).
Precautions
General
Activation of Mania/Hypomania
During premarketing
testing, hypomania or mania occurred in approximately 1.0% of unipolar patients
treated with Paxil compared to 1.1% of active-control and 0.3% of placebo-treated
unipolar patients. In a subset of patients classified as bipolar, the rate
of manic episodes was 2.2% for Paxil and 11.6% for the combined active-control
groups. As with all drugs effective in the treatment of major depressive disorder,
Paxil should be used cautiously in patients with a history of mania.
Seizures
During premarketing testing, seizures occurred in 0.1% of
patients treated with Paxil, a rate similar to that associated with other
drugs effective in the treatment of major depressive disorder. Paxil should
be used cautiously in patients with a history of seizures. It should be discontinued
in any patient who develops seizures.
Discontinuation of Treatment With Paxil
Recent clinical trials supporting the various approved indications
for Paxil employed a taper-phase regimen, rather than an abrupt discontinuation
of treatment. The taper-phase regimen used in GAD and PTSD clinical trials
involved an incremental decrease in the daily dose by 10 mg/day at weekly
intervals. When a daily dose of 20 mg/day was reached, patients were
continued on this dose for 1 week before treatment was stopped.
With
this regimen in those studies, the following adverse events were reported
at an incidence of 2% or greater for Paxil and were at least twice that reported
for placebo: Abnormal dreams, paresthesia, and dizziness. In the majority
of patients, these events were mild to moderate and were self-limiting and
did not require medical intervention.
During marketing
of Paxil and other SSRIs and SNRIs, there have been spontaneous reports of
adverse events occurring, upon the discontinuation of these drugs (particularly
when abrupt), including the following: Dysphoric mood, irritability, agitation,
dizziness, sensory disturbances (e.g., paresthesias such as electric shock
sensations and tinnitus), anxiety, confusion, headache, lethargy, emotional
lability, insomnia, and hypomania. While these events are generally self-limiting,
there have been reports of serious discontinuation symptoms.
Patients
should be monitored for these symptoms when discontinuing treatment with Paxil.
A gradual reduction in the dose rather than abrupt cessation is recommended
whenever possible. If intolerable symptoms occur following a decrease in the
dose or upon discontinuation of treatment, then resuming the previously prescribed
dose may be considered. Subsequently, the physician may continue decreasing
the dose but at a more gradual rate (see DOSAGE AND ADMINISTRATION).
See
also PRECAUTIONS—Pediatric Use, for adverse events reported upon discontinuation
of treatment with Paxil in pediatric patients.
Akathisia
The use of paroxetine or other SSRIs has been associated
with the development of akathisia, which is characterized by an inner sense
of restlessness and psychomotor agitation such as an inability to sit or stand
still usually associated with subjective distress. This is most likely to
occur within the first few weeks of treatment.
Hyponatremia
Several cases of hyponatremia have been reported. The hyponatremia
appeared to be reversible when Paxil was discontinued. The majority of these
occurrences have been in elderly individuals, some in patients taking diuretics
or who were otherwise volume depleted.
Serotonin Syndrome
The development of a serotonin syndrome may occur in association
with treatment with paroxetine, particularly with concomitant use of serotonergic
drugs and with drugs which may have impaired metabolism of paroxetine. Symptoms
have included agitation, confusion, diaphoresis, hallucinations, hyperreflexia,
myoclonus, shivering, tachycardia, and tremor. The concomitant use of Paxil
with serotonin precursors (such as tryptophan) is not recommended (see WARNINGS—Potential
for Interaction with Monoamine Oxidase Inhibitors and PRECAUTIONS—Drug
Interactions).
Abnormal Bleeding
Published case reports have documented the occurrence of
bleeding episodes in patients treated with psychotropic agents that interfere
with serotonin reuptake. Subsequent epidemiological studies, both of the case-control
and cohort design, have demonstrated an association between use of psychotropic
drugs that interfere with serotonin reuptake and the occurrence of upper gastrointestinal
bleeding. In 2 studies, concurrent use of a nonsteroidal anti-inflammatory
drug (NSAID) or aspirin potentiated the risk of bleeding (see Drug Interactions).
Although these studies focused on upper gastrointestinal bleeding, there is
reason to believe that bleeding at other sites may be similarly potentiated.
Patients should be cautioned regarding the risk of bleeding associated with
the concomitant use of paroxetine with NSAIDs, aspirin, or other drugs that
affect coagulation.
Use in Patients With Concomitant Illness
Clinical experience with Paxil in patients with certainconcomitant systemic illness is limited. Caution is advisable in using Paxil
in patients with diseases or conditions that could affect metabolism or hemodynamic
responses.
As with other SSRIs, mydriasis has been
infrequently reported in premarketing studies with Paxil. A few cases of acute
angle closure glaucoma associated with paroxetine therapy have been reported
in the literature. As mydriasis can cause acute angle closure in patients
with narrow angle glaucoma, caution should be used when Paxil is prescribed
for patients with narrow angle glaucoma.
Paxil has
not been evaluated or used to any appreciable extent in patients with a recent
history of myocardial infarction or unstable heart disease. Patients with
these diagnoses were excluded from clinical studies during the product’s
premarket testing. Evaluation of electrocardiograms of 682 patients who received
Paxil in double-blind, placebo-controlled trials, however, did not indicate
that Paxil is associated with the development of significant ECG abnormalities.
Similarly, Paxil does not cause any clinically important changes in heart
rate or blood pressure.
Increased plasma concentrations
of paroxetine occur in patients with severe renal impairment (creatinine clearance<30 mL/min.) or severe hepatic impairment. A lower starting dose should
be used in such patients (see DOSAGE AND ADMINISTRATION).
Information for Patients
Prescribers or other health professionals should inform
patients, their families, and their caregivers about the benefits and risks
associated with treatment with Paxil and should counsel them in its appropriate
use. A patient Medication Guide About Using Antidepressants in Children and
Teenagers is available for Paxil. The prescriber or health professional should
instruct patients, their families, and their caregivers to read the Medication
Guide and should assist them in understanding its contents. Patients should
be given the opportunity to discuss the contents of the Medication Guide and
to obtain answers to any questions they may have. The complete text of the
Medication Guide is reprinted at the end of this document.
Patients
should be advised of the following issues and asked to alert their prescriber
if these occur while taking Paxil.
Clinical Worsening and Suicide Risk
Patients, their families, and their caregivers should be
encouraged to be alert to the emergence of anxiety, agitation, panic attacks,
insomnia, irritability, hostility, aggressiveness, impulsivity, akathisia
(psychomotor restlessness), hypomania, mania, other unusual changes in behavior,
worsening of depression, and suicidal ideation, especially early during antidepressant
treatment and when the dose is adjusted up or down. Families and caregivers
of patients should be advised to observe for the emergence of such symptoms
on a day-to-day basis, since changes may be abrupt. Such symptoms should be
reported to the patient’s prescriber or health professional, especially
if they are severe, abrupt in onset, or were not part of the patient’s
presenting symptoms. Symptoms such as these may be associated with an increased
risk for suicidal thinking and behavior and indicate a need for very close
monitoring and possibly changes in the medication.
Drugs That Interfere With Hemostasis (NSAIDs, Aspirin, Warfarin, etc.)
Patients should be cautioned about the concomitant use of
paroxetine and NSAIDs, aspirin, or other drugs that affect coagulation since
the combined use of psychotropic drugs that interfere with serotonin reuptake
and these agents has been associated with an increased risk of bleeding.
Interference With Cognitive and Motor Performance
Any psychoactive drug may impair judgment, thinking, or
motor skills. Although in controlled studies Paxil has not been shown to impair
psychomotor performance, patients should be cautioned about operating hazardous
machinery, including automobiles, until they are reasonably certain that therapy
with Paxil does not affect their ability to engage in such activities.
Completing Course of Therapy
While patients may notice improvement with treatment with
Paxil in 1 to 4 weeks, they should be advised to continue therapy as
directed.
Concomitant Medication
Patients should be advised to inform their physician if
they are taking, or plan to take, any prescription or over-the-counter drugs,
since there is a potential for interactions.
Alcohol
Although Paxil has not been shown to increase the impairment
of mental and motor skills caused by alcohol, patients should be advised to
avoid alcohol while taking Paxil.
Pregnancy
Patients should be advised to notify their physician if
they become pregnant or intend to become pregnant during therapy. (See WARNINGS—Usage
in Pregnancy: Teratogenic and Nonteratogenic
Effects).
Nursing
Patients should be advised to notify their physician if
they are breast-feeding an infant (see PRECAUTIONS—Nursing Mothers).
Laboratory Tests
There are no specific laboratory tests recommended.
Drug Interactions
Tryptophan
As with other serotonin reuptake inhibitors, an interaction
between paroxetine and tryptophan may occur when they are coadministered.
Adverse experiences, consisting primarily of headache, nausea, sweating, and
dizziness, have been reported when tryptophan was administered to patients
taking Paxil. Consequently, concomitant use of Paxil with tryptophan is not
recommended (see Serotonin Syndrome).
Monoamine Oxidase Inhibitors
See CONTRAINDICATIONS and WARNINGS.
Pimozide
In a controlled study of healthy volunteers, after Paxil
was titrated to 60 mg daily, co-administration of a single dose of 2 mg pimozide
was associated with mean increases in pimozide AUC of 151% and Cmax of
62%, compared to pimozide administered alone. Due to the narrow therapeutic
index of pimozide and its known ability to prolong the QT interval, concomitant
use of pimozide and Paxil is contraindicated (see CONTRAINDICATIONS).
Serotonergic Drugs
Based on the
mechanism of action of paroxetine and the potential for serotonin syndrome,
caution is advised when Paxil is coadministered with other drugs or agents
that may affect the serotonergic neurotransmitter systems, such as tryptophan,
triptans, serotonin reuptake inhibitors, linezolid (an antibiotic which is
a reversible non-selective MAOI), lithium, tramadol, or St. John"s Wort (see
Serotonin Syndrome).
Thioridazine
See CONTRAINDICATIONS and WARNINGS.
Warfarin
Preliminary data
suggest that there may be a pharmacodynamic interaction (that causes an increased
bleeding diathesis in the face of unaltered prothrombin time) between paroxetine
and warfarin. Since there is little clinical experience, the concomitant administration
of Paxil and warfarin should be undertaken with caution (see Drugs
That Interfere With Hemostasis ).
Triptans
There have been rare postmarketing reports describing patients
with weakness, hyperreflexia, and incoordination following the use of a selective
serotonin reuptake inhibitor (SSRI) and sumatriptan. If concomitant treatment
with a triptan and an SSRI (e.g., fluoxetine, fluvoxamine, paroxetine, sertraline)
is clinically warranted, appropriate observation of the patient is advised
(see Serotonin Syndrome).
Drugs Affecting Hepatic Metabolism
The metabolism and pharmacokinetics of paroxetine may be
affected by the induction or inhibition of drug-metabolizing enzymes.
Cimetidine
Cimetidine inhibits many cytochrome P450 (oxidative)
enzymes. In a study where Paxil (30 mg once daily) was dosed orally for 4 weeks,
steady-state plasma concentrations of paroxetine were increased by approximately
50% during coadministration with oral cimetidine (300 mg three times
daily) for the final week. Therefore, when these drugs are administered concurrently,
dosage adjustment of Paxil after the 20-mg starting dose should be guided
by clinical effect. The effect of paroxetine on cimetidine’s pharmacokinetics
was not studied.
Phenobarbital
Phenobarbital induces many cytochrome P450 (oxidative)
enzymes. When a single oral 30-mg dose of Paxil was administered at phenobarbital
steady state (100 mg once daily for 14 days), paroxetine AUC and
T½ were reduced (by an average of 25% and 38%, respectively) compared
to paroxetine administered alone. The effect of paroxetine on phenobarbital
pharmacokinetics was not studied. Since Paxil exhibits nonlinear pharmacokinetics,
the results of this study may not address the case where the 2 drugs are both
being chronically dosed. No initial dosage adjustment of Paxil is considered
necessary when coadministered with phenobarbital; any subsequent adjustment
should be guided by clinical effect.
Phenytoin
When a single oral 30-mg dose of Paxil was administered
at phenytoin steady state (300 mg once daily for 14 days), paroxetine
AUC and T½ were reduced (by an average of 50% and 35%, respectively)
compared
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