VENLAFAXINE BESYLATE
Clinical safety rating: caution
MAOIs can cause serotonin syndrome Can increase blood pressure and cause withdrawal symptoms upon discontinuation.
Venlafaxine and its active metabolite desvenlafaxine are potent inhibitors of neuronal serotonin and norepinephrine reuptake, and weak inhibitors of dopamine reuptake. It also has no significant affinity for muscarinic, histaminergic, or alpha-1 adrenergic receptors.
| Metabolism | Primarily metabolized by CYP2D6 to its active metabolite O-desmethylvenlafaxine (desvenlafaxine). Also metabolized by CYP3A4 to a lesser extent. |
| Excretion | Renal: 87% (5% unchanged venlafaxine, 29% unconjugated O-desmethylvenlafaxine, 26% conjugated O-desmethylvenlafaxine, 27% other metabolites). Fecal: minimal (<2%). |
| Half-life | Venlafaxine: 5 ± 2 hours; O-desmethylvenlafaxine (ODV): 11 ± 2 hours. Clinically, the effective half-life is prolonged in hepatic impairment (venlafaxine ~14 h) and severe renal impairment (venlafaxine ~10 h, ODV ~22 h). |
| Protein binding | Venlafaxine: 27% bound; O-desmethylvenlafaxine: 30% bound. Primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Venlafaxine: 7.5 L/kg (large, indicating extensive tissue distribution). Clinical meaning: high penetration into tissues, including brain. |
| Bioavailability | Oral immediate-release: 45% (due to first-pass metabolism); extended-release: comparable. Food does not affect bioavailability. |
| Onset of Action | Oral immediate-release: 1-2 weeks for antidepressant effect (maximal at 4-6 weeks); extended-release: 2-4 weeks. Anticholinergic-like effects may occur within hours. |
| Duration of Action | Immediate-release: dosed 2-3 times daily due to short half-life; extended-release: 24-hour dosing interval. Clinical benefit persists with continued dosing; withdrawal symptoms may occur if discontinued abruptly. |
| Molecular Weight | 313.87 |
For major depressive disorder, generalized anxiety disorder, social anxiety disorder, and panic disorder: initially 37.5 mg po twice daily or 75 mg po once daily for 1 week; then increase to 75 mg po once daily; maximum 225 mg po once daily (immediate-release). For extended-release: 37.5-75 mg po once daily; maximum 225 mg po once daily.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | GFR 30-89 mL/min: reduce total daily dose by 25-50%. GFR <30 mL/min: reduce total daily dose by 50% and administer every other day if needed. Hemodialysis: administer dose after dialysis, reduce by 50%. |
| Liver impairment | Child-Pugh class A or B: reduce total daily dose by 50% (maximum 100 mg/day for immediate-release). Child-Pugh class C: use not recommended due to lack of data. |
| Pediatric use | Children ≥7 years for major depressive disorder: weight <40 kg, starting 37.5 mg po once daily for 1 week, then increase to 75 mg po once daily (extended-release); max 75 mg/day. Weight ≥40 kg: same as adult dosing up to 225 mg/day. Safety and efficacy not established for other indications. |
| Geriatric use | Elderly: use lower initial doses (e.g., 37.5 mg po once daily for extended-release); titrate slowly to minimum effective dose. Maximum dose 225 mg/day, but cautious use recommended. Monitor for hyponatremia and blood pressure. |
| 1st trimester | Venlafaxine crosses the placenta. Epidemiological data suggest no increased risk of major congenital malformations, but a small risk of cardiovascular defects cannot be excluded. Use only if benefit outweighs risk. |
| 2nd trimester | Continued exposure may be associated with risk of preeclampsia, preterm birth, and low birth weight. Monitor for fetal growth and maternal blood pressure. |
| 3rd trimester | Late third-trimester use may lead to neonatal withdrawal syndrome including irritability, feeding difficulties, respiratory distress, and seizures. Tapering before delivery recommended if possible. |
Clinical note
MAOIs can cause serotonin syndrome Can increase blood pressure and cause withdrawal symptoms upon discontinuation.
| FDA category | Animal |
| Placental transfer | Venlafaxine crosses the placenta freely; umbilical cord plasma concentrations are approximately 70-100% of maternal plasma levels. |
■ FDA Black Box Warning
WARNING: Suicidality and Antidepressant Drugs. Antidepressants increased the risk of suicidal thinking and behavior (suicidality) in short-term studies in children, adolescents, and young adults with major depressive disorder (MDD) and other psychiatric disorders. Monitor for worsening and emergence of suicidal thoughts and behaviors.
| Common Effects | anxiety disorders |
| Serious Effects |
Hypersensitivity to venlafaxine or any excipientsConcomitant use with MAOIs (monoamine oxidase inhibitors) or within 14 days of discontinuing an MAOI
| Precautions | Clinical worsening and suicide risk (monitor closely), Serotonin syndrome (especially with other serotonergic drugs), Elevated blood pressure (dose-dependent), Activation of mania/hypomania, Seizure risk (use cautiously in patients with seizure disorders), Angle-closure glaucoma (may cause mydriasis), Hyponatremia (SIADH risk, especially in elderly/dehydrated), Abnormal bleeding (NSAIDs, aspirin use), Interstitial lung disease and eosinophilic pneumonia (rare), Sexual dysfunction, Discontinuation syndrome (taper dose gradually) |
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| Breastfeeding | Venlafaxine and its active metabolite desvenlafaxine are excreted into breast milk in low to moderate amounts. Relative infant dose is approximately 5-8% of maternal weight-adjusted dose. Monitor infant for drowsiness and adequate weight gain. Most studies report no adverse effects. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | First trimester: Epidemiologic studies have not established a consistent association between venlafaxine use and major congenital malformations. However, some studies suggest a small increased risk of cardiovascular malformations (e.g., ventricular septal defects) with first-trimester exposure. Second and third trimesters: Exposure may increase risk for preterm birth, low birth weight, and neonatal adaptation syndrome (including irritability, feeding difficulties, respiratory distress, and seizures). Late third-trimester exposure is associated with persistent pulmonary hypertension of the newborn (PPHN) and poor neonatal adaptation requiring prolonged hospitalization. Overall, the absolute risks are low, and the benefits of treating maternal depression may outweigh potential risks. |
| Fetal Monitoring | Maternal: Monitor for worsening depression, suicidal ideation, and serotonin syndrome (especially with concurrent serotonergic drugs). Assess blood pressure regularly due to dose-dependent hypertension. Monitor for signs of bleeding (venlafaxine may increase risk of postpartum hemorrhage). Fetal/neonatal: Monitor for neonatal adaptation syndrome (respiratory distress, feeding difficulties, jitteriness, seizures) for at least 48 hours after delivery. Consider ultrasound for fetal growth if exposure in second/third trimester. No specific fetal monitoring required solely due to venlafaxine exposure. |
| Fertility Effects | Animal studies have shown no impairment of fertility at clinically relevant doses. In humans, venlafaxine may cause sexual dysfunction (e.g., decreased libido, delayed ejaculation) which could affect fertility indirectly. There is no evidence of permanent effects on fertility. Discontinuation of venlafaxine may be considered in patients planning pregnancy, but risks of untreated depression should be weighed. |
| Food/Dietary | No specific food interactions; however, high-fat meals may delay absorption slightly. Avoid alcohol due to potential additive CNS effects and hepatotoxicity. |
| Clinical Pearls | Venlafaxine is a serotonin-norepinephrine reuptake inhibitor (SNRI) with a short half-life; abrupt discontinuation can cause withdrawal symptoms including dizziness, nausea, and paresthesias. Monitor blood pressure regularly as dose-dependent hypertension is common, especially at doses >225 mg/day. Use with caution in patients with uncontrolled hypertension or seizure history. Therapeutic response typically seen at 150-225 mg/day; lower doses primarily affect serotonin. Avoid use within 14 days of MAOIs. |
| Patient Advice | Take with food to reduce nausea; avoid taking later than 4 PM to minimize insomnia. · Do not stop taking this medication abruptly; taper under medical supervision to avoid withdrawal symptoms. · May cause increased blood pressure; monitor regularly and report headaches or blurred vision. · Report any suicidal thoughts or worsening depression, especially during first few weeks. · Avoid alcohol as it may increase CNS depression and hepatotoxicity risk. |