Section 3.2.2.3

Venlafaxine

General Description

Venlafaxine (effexor) is a novel phenylethylamine that is structurally distinct from existing antidepressant drugs and possesses a slightly different mechanism of action. It may have a faster than usual onset of action and greater efficacy in some depressed patients (for example, patients with melancholic features) than other antidepressants, especially when higher initial doses are used.

Indications for Medication

Venlafaxine is used for the treatment of major depressive disorder. Preliminary reports from the psychiatric literature indicate that the drug may also be useful in the treatment of attention deficit, hyperactivity disorder and pain syndromes.

Clinical Guidelines

The usual starting dose of venlafaxine is 25-75mg a day, given in two or three divided doses. The dosage can be raised to 150mg a day, given in two or three divided doses, after an appropriate period of clinical assessment at the lower 75mg dose (usually 2-3 weeks).

Most patients will respond to a dose of 75mg of venlafaxine. However, some patients may benefit from a higher dosage. Venlafaxine may be increased as often as every four days in increments of 75mg a day. Dosages of over 300mg a day should be given in three divided doses. The maximum dosage of venlafaxine is 375mg a day.

Adverse Effects

The most common adverse effects are nausea, headache, somnolence, dry mouth, dizziness, nervousness, constipation and asthenia. Less common side effects include anxiety, anorexia, blurred vision, abnormal ejaculation or orgasm and impotence.

A rapid withdrawal of venlafaxine may cause nausea, somnolence and insomnia. To prevent withdrawal symptoms, the venlafaxine should be slowly tapered as it is discontinued.

At high doses of venlafaxine (over 300mg a day), there is an effect on increased blood pressure. Patients who are taking high doses of venlafaxine should have their blood pressure closely monitored.

Information concerning the use of venlafaxine in pregnancy is not available at this time. Venlafaxine should therefore be avoided in pregnant women and in nursing mothers.

Drug-Drug Interactions

The drug-drug interactions of venlafaxine do not appear extensive. There is no evidence that venlafaxine interacts with lithium, diazepam or ethanol. More of these interactions need to be studied.

Venlafaxine should not be used in combination with a MAOI. There should be a 14-day washout period after the MAOI before initiating venlafaxine treatment. There should be at least 7 days before starting a MAOI after stopping venlafaxine.

For additional possible drug-drug interactions, the clinician should check the PDR for further information.

The consent form for this medication is "Antidepressant (Anti-Obsessive-Compulsive Medication / Tricyclics & Similarly Acting Medications)."