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Venlafaxine

Definition

Venlafaxine is an antidepressant available in the United States under the trade name of Effexor or Effexor XR.

Purpose

Venlafaxine is used to treat depression and generalized anxiety disorder. It has also been used to treat obsessive-compulsive disorderand irritable bowel syndrome.

Description

Venlafaxine is an antidepressant. It has actions common to both the cyclic antidepressants such as imipramine(Tofranil) and amitriptyline(Elavil,) and the selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac), sertraline(Zoloft), and paroxetine(Paxil). It is believed to derive its actions by increasing levels of both norepinephrine and serotonin in the brain.

The therapeutic effects of venlafaxine, like other antidepressants, appear slowly. Maximum benefit is often not evident for at least two weeks after starting the drug. People taking venlafaxine should be aware of this and continue taking the drug as directed even if they do not see immediate improvement.

Venlafaxine is broken down by the liver and eliminated from the body by the kidneys. As a result, the dose of venlafaxine must be lowered in people with liver or kidney disease.

Venlafaxine is available in 25-mg, 37.5-mg, 50-mg, 75-mg, and 100-mg rapid-release tablets and 75-mg and 150-mg extended-action capsules.

Recommended dosage

The recommended initial dose of venlafaxine is 75 mg daily taken as two or three equal doses. The dose may be increased in 75-mg increments every four days as needed until symptoms of depression or anxiety resolve. Most commonly, dosages range between 150 mg to 225 mg daily. although in severe situations, 375 mg per day may be needed. Once patients are stabilized using the rapid-acting tablets, they may be converted over to the appropriate dose of extended-release capsules.

In people with liver disease, the daily dosage of venlafaxine should be cut in half. In patients with kidney disease, the daily dosage of venlafaxine should be reduced 25–50%, depending upon the extent of kidney damage. When stopping venlafaxine, the dosage should be reduced gradually over a period of at least two weeks before the drug is totally stopped.

Precautions

Patients taking venlafaxine should be monitored closely for insomnia, anxiety, mania, significant weight loss, seizures, and thoughts of suicide.

Caution should also be exercised when prescribing venlafaxine to patients with impaired liver or kidney function, the elderly (over age 60) children, individuals with known manic-depressive disorder or a history of seizures, people with diabetes, and individuals expressing ideas of committing suicide.

Individuals should not take MAO inhibitors such as Nardil during venlafaxine therapy, for two weeks prior to beginning venlafaxine therapy, and for five weeks after stopping venlafaxine therapy.

Care should be taken to weigh the risks and benefit of this drug in women who are, or wish to become, pregnant, as well as in breast-feeding mothers.

People with diabetes should monitor their blood or urine sugar more carefully, since venlafaxine may affect blood sugar.

Until an individual understands the effects that venlafaxine may have, he or she should avoid driving, operating dangerous machinery, or participating in hazardous activities. Alcohol should not be used while taking venlafaxine.

Side effects

More common side effects include decreased sexual drive, restlessness, difficulty sitting still, skin rash, hives, and itching.

Less common side effects include fever and/or chills, and pain in joints or muscles.

Rare side effects include pain or enlargement of breasts and/or abnormal milk production in women, seizures, fast heart rate, irregular heartbeats, red or purple spots on the skin, low blood sugar and its symptoms (anxiety, chills, cold sweats, confusion, difficulty concentrating, drowsiness, excess hunger, rapid heart rate, headache, shakiness or unsteadiness, severe fatigue), low blood sodium and its symptoms (including confusion, seizures, drowsiness, dry mouth, severe thirst, decreased energy), serotonin syndrome (usually at least three of the following: diarrhea, fever, sweatiness, mood or behavior changes, overactive reflexes, fast heart rate, restlessness, shivering or shaking), excitability, agitation, irritability, pressured talking, difficulty breathing, and odd body or facial movements.

Interactions

Venlafaxine interacts with a long list of other medications. Anyone starting this drug should review the other medications they are taking with their physician and pharmacist for possible interactions. Patients should always inform all their health care providers, including dentists, that they are taking venlafaxine.

Dangerously high blood pressure, rapid changes in heart rate, high fever, muscle stiffness, and sudden muscle spasms have resulted from the combination of antidepressants, such as venlafaxine, and members of another class of antidepressants known as monoamine oxidase (MAO) inhibitors. Because of these serious adverse reactions, venlafaxine should never be taken in combination with MAO inhibitors. Patient taking any MAO inhibitors, for example Nardil (phenelzinesulfate) or Parmate (tranylcyprominesulfate), should stop the MAO inhibitor then wait at least 14 days before starting venlafaxine or a tricyclic antidepressant. The same holds true when discontinuing venlafaxine and starting an MAO inhibitor.

Some other drugs such as trazodone(Desyrel), sibutramine (Meridia), and sumatriptan (Imitrex) also interact with venlafaxine and cause a syndrome known as neuroleptic malignant syndrome, characterized by irritability, muscle stiffness, shivering, muscle spasms, and altered consciousness.

The sedative effects (drowsiness, lack of mental clarity) of venlafaxine are increased by other central nervous system depressants such as alcohol, sedatives, sleeping medications, or other medications used for mental disorders such as schizophrenia.

Resources

BOOKS

Facts and Comparisons Staff. Drug Facts and Comparisons.6th Edition. St. Louis, MO: Facts and Comparisons,2002.

Mosby Staff. Mosby's Medical Drug Reference.St. Louis, MO: Mosby, Inc, 1999.

Wyeth Laboratories Staff. Effexor Package Insert.Philadelphia, PA: Wyeth Laboratories, 2001.

Kelly Karpa, RPh, Ph.D.