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 doxepin
hydrochloride and should counsel them in its appropriate use. A patient
Medication Guide about “Antidepressant Medicines, Depression and other Serious
Mental Illness, and Suicidal Thoughts or Actions” is available for doxepin
hydrochloride. 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 doxepin hydrochloride.
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
look 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.
Pediatric Use: Safety and effectiveness in the pediatric
population have not been established (see BOX WARNING
and WARNINGS – Clinical Worsening and Suicide
Risk). Anyone considering the use of doxepin HCl in a child or adolescent
must balance the potential risks with the clinical need.
Drug Interactions
Drugs Metabolized by P450 2D6: The biochemical activity of
the drug metabolizing isozyme cytochrome P450 2D6 (debrisoquin hydroxylase) is
reduced in a subset of the Caucasian population (about 7-10% of Caucasians are
so-called “poor metabolizers”); reliable estimates of the prevalence of reduced
P450 2D6 isozyme activity among Asian, African and other populations are not yet
available. Poor metabolizers have higher than expected plasma concentrations of
tricyclic antidepressants (TCAs) when given usual doses. Depending on the
fraction of drug metabolized by P450 2D6, the increase in plasma concentration
may be small, or quite large (8-fold increase in plasma AUC of the TCA).
In addition, certain
drugs inhibit the activity of this isozyme and make normal metabolizers resemble
poor metabolizers. An individual who is stable on a given dose of TCA may become
abruptly toxic when given one of these inhibiting drugs as concomitant therapy.
The drugs that inhibit cytochrome P450 2D6 include some that are not metabolized
by the enzyme (quinidine; cimetidine) and many that are substrates for P450 2D6
(many other antidepressants, phenothiazines, and the Type 1C antiarrhythmics
propafenone and flecainide). While all the selective serotonin reuptake
inhibitors (SSRIs), e.g., fluoxetine, sertraline, and paroxetine, inhibit P450
2D6, they may vary in the extent of inhibition. The extent to which SSRI-TCA
interactions may pose clinical problems will depend on the degree of inhibition
and the pharmacokinetics of the SSRI involved. Nevertheless, caution is
indicated in the co-administration of TCAs with any of the SSRIs and also in
switching from one class to the other. Of particular importance, sufficient time
must elapse before initiating TCA treatment in a patient being withdrawn from
fluoxetine, given the long half-life of the parent and active metabolite (at
least 5 weeks may be necessary).
Concomitant use of
tricyclic antidepressants with drugs that can inhibit cytochrome P450 2D6 may
require lower doses than usually prescribed for either the tricyclic
antidepressant or the other drug. Furthermore, whenever one of these other drugs
is withdrawn from co-therapy, an increased dose of tricyclic antidepressant may
be required. It is desirable to monitor TCA plasma levels whenever a TCA is
going to be co-administered with another drug known to be an inhibitor of P450
2D6.
Doxepin is primarily
metabolized by CYP2D6 (with CYP1A2 & CYP3A4 as minor pathways). Inihibitors
or substrates of CYP2D6 (i.e., quinidine, selective serotonin reuptake
inhibitors [SSRIs]) may increase the plasma concentration of doxepin when
administered concomitantly. The extent of interaction depends on the variability
of effect on CYP2D6. The clinical significance of this interaction with doxepin
has not been systematically evaluated.
MAO
Inhibitors
Serious side effects and
even death have been reported following the concomitant use of certain drugs
with MAO inhibitors. Therefore, MAO inhibitors should be discontinued at least
two weeks prior to the cautious initiation of therapy with doxepin HCl. The
exact length of time may vary and is dependent upon the particular MAO inhibitor
being used, the length of time it has been administered, and the dosage
involved.
Cimetidine
Cimetidine has been
reported to produce clinically significant fluctuations in steady-state serum
concentrations of various tricyclic antidepressants. Serious anticholinergic
symptoms (i.e., severe dry mouth, urinary retention and blurred vision) have
been associated with elevations in the serum levels of tricyclic antidepressants
when cimetidine therapy is initiated. Additionally, higher than expected
tricyclic antidepressant levels have been observed when they are begun in
patients already taking cimetidine. In patients who have been reported to be
well controlled on tricyclic antidepressants receiving concurrent cimetidine
therapy, discontinuation of cimetidine has been reported to decrease established
steady-state serum tricyclic antidepressant levels and compromise their
therapeutic effects.
Alcohol
It should be borne in
mind that alcohol ingestion may increase the danger inherent in any intentional
or unintentional doxepin HCl overdosage. This is especially important in
patients who may use alcohol excessively.
Tolazamide
A case of severe
hypoglycemia has been reported in a type II diabetic patient maintained on
tolazamide (1 gm/day) 11 days after the addition of doxepin (75 mg/day).
Drowsiness
Since drowsiness may
occur with the use of this drug, patients should be warned of the possibility
and cautioned against driving a car or operating dangerous machinery while
taking the drug. Patients should also be cautioned that their response to
alcohol may be potentiated.
Sedating drugs may cause
confusion and over sedation in the elderly; elderly patients generally should be
started on low doses of doxepin HCl and observed closely (see PRECAUTIONS-Geriatric Use).
Suicide
Since suicide is an
inherent risk in any depressed patient and may remain so until significant
improvement has occurred, patients should be closely supervised during the early
course of therapy. Prescriptions should be written for the smallest feasible
amount.
Psychosis
Should increased
symptoms of psychosis or shift to manic symptomatology occur, it may be
necessary to reduce dosage or add a major tranquilizer dosage regimen.
Pediatric Use
Safety and effectiveness
in the pediatric population have not been established (see BOX
WARNING and WARNINGS- Clinical Worsening and Suicide
Risk). Anyone considering the use of doxepin HCl in a child or adolescent
must balance the potential risks with the clinical need.
Geriatric Use
A determination has not
been made whether controlled clinical studies of doxepin HCl included sufficient
numbers of subjects aged 65 and over to define a difference in response from
younger subjects. Other reported clinical experience has not identified
differences in responses between the elderly and younger patients. In general,
dose selection for an elderly patient should be cautious, usually starting at
the low end of the dosing range, reflecting the greater frequency of decreased
hepatic, renal or cardiac function, and of concomitant disease or other drug
therapy.
The extent of renal
excretion of doxepin HCl has not been determined. Because elderly patients are
more likely to have decreased renal function, care should be taken in dose
selections.
Sedating drugs may cause
confusion and over sedation in the elderly; elderly patients generally should be
started on low doses of doxepin HCl and observed closely. (See WARNINGS.)