VENLAFAXINE

(ven-la-fax'een)

Effexor, Effexor XR
Classifications: psychotherapeutic; antidepressant; serotonin norepinephrine reuptake inhibitor (snri);
Therapeutic: antidepressant (snri)
Pregnancy Category: C

Availability

25 mg, 37.5 mg, 50 mg, 75 mg, 100 mg tablets; 37.5 mg, 75 mg, 150 mg sustained release capsules

Action

Potent inhibitor of neuronal serotonin and norepinephrine reuptake and weak inhibitor of dopamine reuptake.

Therapeutic Effect

Antidepressant effect presumed to be due to potentiation of neurotransmitter activity in the CNS.

Uses

Depression, generalized anxiety disorder; social anxiety disorder.

Unlabeled Uses

Obsessive-compulsive disorder.

Contraindications

Hypersensitivity to venlafaxine, or other SNRI drugs; concurrent administration with MAO inhibitors; abrupt discontinuation; neonates; pregnancy (category C), lactation.

Cautious Use

Renal and hepatic impairment, renal failure; anorexia nervosa, history of mania, suicidal ideations; elevated intraocular pressure, acute closed-angle glaucoma; cardiac disorders, recent MI, heart failure; hypertension; hyperthyroidism; concomitant administration with CNS drugs, CNS depression; history of seizures or seizure disorders; older adults. Safety in children <18 y is not established.

Route & Dosage

Depression
Adult: PO 25–125 mg t.i.d.
Geriatric: PO Start with lower doses in older adults

Anxiety
Adult: PO Start with 37.5 mg sustained release q.d. and increase to 75–225 mg sustained release per day

Renal Impairment
Cl_cr 10–70 mL/min: reduce total daily dose by 25–50%; <10 mL/min: reduce total daily dose by 50%

Administration

Oral

Give with food. Sustained release capsules must be swallowed whole, must not be opened or chewed.
Dosage increments of up to 75 mg/d are usually made at 4 d or longer intervals.
Allow 14 d interval after discontinuing an MAO inhibitor before starting venlafaxine.
Do not abruptly withdraw drug after 1 wk or more of therapy.
Store at room temperature, 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

CV: Increased blood pressure and heart rate, palpitations. CNS: Dizziness, fatigue, headache, anxiety, insomnia, somnolence. Endocrine: Small but statistically significant increase in serum cholesterol, weight loss (approximately 3 lb). GI: Nausea, vomiting, dry mouth, constipation. Urogenital: Sexual dysfunction, erectile failure, delayed orgasm, anorgasmia, impotence, abnormal ejaculation. Special Senses: Blurred vision. Body as a Whole: Sweating, asthenia.

Interactions

Drug: Cimetidine, mao inhibitors, desipramine, haloperidol may increase venlafaxine levels and toxicity. Should not use in combination with mao inhibitors: do not start until >14 d after stopping mao inhibitor; do not start mao inhibitor until 7 d after stopping venlafaxine. Trazodone may lead to serotonin syndrome. Herbal: St. John's wort, sour date nut may cause serotonin syndrome.

Pharmacokinetics

Absorption: Well absorbed from GI tract. Onset: 2 wk. Peak: Venlafaxine 1–2 h; metabolite 3–4 h. Duration: Approximately 30% protein bound, but extensively tissue bound. Metabolism: Undergoes substantial first-pass metabolism to its major active metabolite, O-desmethylvenlafaxine, with similar activity to venlafaxine. Elimination:

60% in urine as parent compound and metabolites. Half-Life: Venlafaxine 3–4 h, O-desmethylvenlafaxine 10 h.

Nursing Implications

Assessment & Drug Effects

Monitor for worsening of depression or emergence of suicidal ideation.
Monitor cardiovascular status periodically with measurements of HR and BP.
Lab tests: Periodic lipid profile.
Monitor neurologic status and report excessive anxiety, nervousness, and insomnia.
Monitor weight periodically and report excess weight loss.
Assess safety, as dizziness and sedation are common.

Patient & Family Education

Be aware of potential adverse effects and notify physician of those that are bothersome.
Do not drive or engage in potentially hazardous activities until response to drug is known.
Avoid using alcohol while on venlafaxine.
Do not use herbal medications without consulting physician.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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