OVERDOSE
Human Experience
Immediate-Release Tablets: There
were 14 reports of acute overdose with venlafaxine hydrochloride,
either alone or in combination with other drugs and/or
alcohol, among the patients included in the premarketing
evaluation. The majority of the reports involved ingestions
in which the total dose of venlafaxine HCl taken was estimated
to be no more than several-fold higher than the usual
therapeutic dose. The 3 patients who took the highest
doses were estimated to have ingested approximately 6.75
g, 2.75 g and 2.5 g. The resultant peak plasma levels
of venlafaxine for the latter 2 patients were 6.24 and
2.35 mcg/ml, respectively, and the peak plasma levels
of O-desmethylvenlafaxine were 3.37 and 1.30 mcg/ml, respectively.
Plasma venlafaxine levels were not obtained for the patient
who ingested 6.75 g of venlafaxine. All 14 patients recovered
without sequelae. Most patients reported no symptoms.
Among the remaining patients, somnolence was the most
commonly reported symptom. The patient who ingested 2.75
g of venlafaxine was observed to have 2 generalized convulsions
and a prolongation of QTc to 500 msec, compared with 405
msec at baseline. Mild sinus tachycardia was reported
in 2 of the other patients.
In postmarketing experience, there have been reports
of fatalities in patients taking overdoses of venlafaxine,
predominantly in combination with alcohol and/or other
drugs.
Extended-Release Capsules:
Among the patients included in the premarketing evaluation
of venlafaxine HCl (extended release), there were 2 reports
of acute overdosage with venlafaxine HCl (extended release),
either alone or in combination with other drugs. One patient
took a combination of 6 g of venlafaxine HCl (extended
release) and 2.5 mg of lorazepam. This patient was hospitalized,
treated symptomatically, and recovered without any untoward
effects. The other patient took 2.85 g of venlafaxine
HCl (extended release). This patient reported paresthesia
of all four limbs but recovered without sequelae.
There were 2 reports of acute overdose with venlafaxine
HCl extended-release in GAD trials. One patient took a
combination of 0.75 g of venlafaxine HCl extended-release
and 200 mg of paroxetine and 50 mg of zolpidem. This patient
was described as being alert, able to communicate, and
a little sleepy. This patient was hospitalized, treated
with activated charcoal, and recovered without any untoward
effects. The other patient took 1.2 g of venlafaxine HCl
extended-release. This patient recovered and no other
specific problems were found. The patient had moderate
dizziness, nausea, numb hands and feet, and hot-cold spells
5 days after the overdose. These symptoms resolved over
the next week.
Overdosage Management
Treatment should consist of those general measures employed
in the management of overdosage with any antidepressant.
Ensure an adequate airway, oxygenation, and ventilation.
Monitoring of cardiac rhythm and vital signs is recommended.
General supportive and symptomatic measures are also recommended.
Use of activated charcoal, induction of emesis, or gastric
lavage should be considered. Due to the large volume of
distribution of venlafaxine hydrochloride, forced durese,
dialysis, hemoperfusion and exchange transfusion are unlikely
to be of benefit. No specific antidotes for venlafaxine
HCl are known.
In managing overdosage, consider the possibility of multiple
drug involvement. The physician should consider contacting
a poison control center on the treatment of any overdose.
CONTRAINDICATIONS
Venlafaxine hydrochloride is contraindicated in patients
known to be hypersensitive to it.
Concomitant use in patients taking monoamine oxidase
inhibitors (MAOIs) is contraindicated (see WARNINGS).
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