- What is venlafaxine (Effexor)?
Venlafaxine (Effexor) is a new antidepressant with a
novel chemical structure. Venlafaxine has a structure that does not resemble
those of any currently used antidepressants. Effexor is not a tricyclic
antidepressant or an MAO inhibitor.
- How does venlafaxine differ from other antidepressants?
Venlafaxine seems to have the relative freedom from
side-effects associated with the SSRIs [fluoxetine (Prozac), sertraline
(Zoloft), paroxetine (Paxil), and fluvoxamine (Luvox)] and the impact on
both serotonin and norepinephrine associated with the tricyclic
antidepressants [amitriptyline (Elavil), imipramine (Tofranil), etc.]. It is
hypothesized that the action of the venlafaxine molecule upon both serotonin
and norepinephrine will cause venlafaxine to be a successful antidepressant
for some people who have not responded to treatment with SSRIs.
As venlafaxine and its active metabolite have
relatively short half-lives, 4 hours and 11 hours respectively, venlafaxine
should be administered in divided does, two or three times a day.
- What kinds of depression can be treated with
venlafaxine?
While the pre-marketing studies were restricted to
patients with a DSM-III-R diagnosis of Major Depressive Disorder (with or
without melancholia), it is to be expected that venlafaxine will be
prescribed for patients with Major Depression, Dysthymia, and Bipolar
Disorder.
While venlafaxine was only studied for periods up to 6
weeks, it is to expected that patients with long-standing depressions will
take the drug for longer periods of time.
- Other than depression, what is treated with venlafaxine?
There is accumulating evidence that the symptoms of
ADD/ADHD in both children and adults can be treated with venlafaxine. High
doses of venlafaxine have also been reported to be effective in the
treatment of people with borderline personality disorder.
- What are the side-effects of venlafaxine?
The most common side-effects and the percentage of
people reporting them during clinical trials are:
| Side-effect |
Patients |
| Nausea |
37% |
| Headache |
25% |
| Sleepiness |
23% |
| Dry mouth |
22% |
| Dizziness |
19% |
| Insomnia |
18% |
| Constipation |
15% |
| Nervousness |
13% |
| Raised blood
pressure |
13% |
| Fatigue |
12% |
| Sweating |
12% |
| Decreased appetite |
11% |
| Male sexual
dysfunction |
12% |
| Female sexual
dysfunction |
2% |
* While the manufacturer says that hypertension only occurs in patients
receiving over 300 mg/day, there have been reports of moderately severe
hypertension in patients taking smaller doses.
- Which side-effects force people to stop taking
venlafaxine?
In the premarketing studies 19% (537 out of the 2897)
of depressed patients taking venlafaxine discontinued the medication because
of side-effects. The side-effects and the percentages of total patients who
dropped out for each are:
| Side-effect |
Patients |
| Nausea |
6% |
| Sleepiness |
3% |
| Insomnia |
3% |
| Dizziness |
3% |
| Male sexual dysfunction |
3% |
| Headache |
2% |
| Nervousness |
2% |
| Anxiety |
2% |
| Dry mouth |
2% |
| Fatigue |
2% |
| Sweating |
2% |
- Are there any special hazards for people with bipolar
disorder?
As with other antidepressants, people with bipolar
disorder who are not being treated with a mood regulator such as lithium,
valproate (Depakote), or carbamazepine (Tegretol) may be pushed into a manic
episode when treated with venlafaxine.
- Does venlafaxine interact with other medications?
Lithium - No interaction.
Diazepam (Valium) - No interaction.
Cimetidine (Tagamet) - Slight increase in blood level
of venlafaxine's active metabolite. Not of clinical significance.
Fluoxetine (Prozac) - Significant increase in the
concentration of venlafaxine and its active metabolite. Potential for
increased side-effects.
- Does venlafaxine interact with alcohol?
Although venlafaxine has not been found to increase
the impairment of cognitive or motor skills caused by alcohol, the
manufacturer warns against drinking while taking venlafaxine.
- Is venlafaxine safe for a woman who is pregnant, about
to become pregnant, or nursing an infant?
There is no data to establish the safety of
venlafaxine for the fetus or nursing infant.
- Is venlafaxine a satisfactory antidepressant for
children and adolescents?
Although here have been no published studies on the
use of venlafaxine for the treatment of children and adolescents with
depression, it is expected that the drug will be prescribed for depressed
children and adolescents.
- Is venlafaxine a satisfactory antidepressant for the
elderly?
No special problems were encountered when venlafaxine
was prescribed for elderly people with depression.
- How is treatment with venlafaxine initiated?
I usually start adults on 25 mg of venlafaxine every
12 hours. Every five days, I usually add 25 mg to each dose until the
patient either responds or reaches reaches 150/day. If there is no response
within 2 weeks of reaching 150 mg/day the dose is again increased in steps
of 25 mg/dose until a total daily dose of 300 mg/day is achieved. If this
dose is not effective, and the patient is tolerating the venlafaxine without
problems, I then increase the dose to between 500 and 600 mg/day.
When venlafaxine is given to elderly patients the
starting dose is the same as for other adults. As older people may be more
sensitive to increases in dose those increases should be made slowly.
- What is the usual final dose of venlafaxine?
While doses up to 375 mg per day are approved by the
FDA, some severely depressed patients have been treated with higher doses.
Most depressed people respond to doses under 300 mg per day.
- How long does it take venlafaxine to relieve
depression?
While most people taking venlafaxine become aware of
some lessening of depression within two to four weeks, there are some who
experience relief within the first week and others who only experience
relief after a couple of months of therapy.
- Are there withdrawal effects if venlafaxine is suddenly
discontinued?
Because of its very short half-life, venlafaxine
should be discontinued gradually over at least 2 weeks. If venlafaxine is
suddenly discontinued, a withdrawal syndrome involving fatigue, nausea,
dizziness, headache, insomnia, and nervousness may develop.
- Is venlafaxine toxic if an overdose is taken?
Fourteen overdoses of venlafaxine have been reported.
In some cases venlafaxine was taken along with alcohol and/or other
medications. All individuals who took an overdose recovered without sequelae.
- What precautions are necessary when switching between
venlafaxine and an MAO inhibitor?
When switching from an MAO inhibitor to venlafaxine,
there should be a 14-day interval between the discontinuation of the MAOI
and the initiation of venlafaxine therapy. When switching from venlafaxine
to an MAOI, a 7-day interval is adequate because of venlafaxine's short
half-life.
- Might venlafaxine be effective when a person has not
responded to other antidepressants?
In patients who have not responded to three
antidepressants from at least two of the major classes of antidepressants,
venlafaxine was found to be effective in nearly one-half of the people with
depression who took it.
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