VENLAFAXINE HYDROCHLORIDE
Clinical safety rating: caution
MAOIs can cause serotonin syndrome Can increase blood pressure and cause withdrawal symptoms upon discontinuation.
Venlafaxine is a serotonin-norepinephrine reuptake inhibitor (SNRI). It potentiates neurotransmitter activity in the central nervous system by inhibiting the reuptake of serotonin and norepinephrine, and to a lesser extent, dopamine.
| Metabolism | Primarily hepatic via CYP2D6 to O-desmethylvenlafaxine (ODV), an active metabolite. Also metabolized by CYP3A4 to N-desmethylvenlafaxine. ODV is further metabolized by conjugation and oxidation. |
| Excretion | Renal elimination: approximately 87% of a dose is recovered in urine within 48 hours as unchanged venlafaxine (5%), unconjugated O-desmethylvenlafaxine (29%), conjugated O-desmethylvenlafaxine (26%), and other minor metabolites (27%). Fecal excretion: negligible, <2%. |
| Half-life | Venlafaxine: 5 ± 2 hours. O-desmethylvenlafaxine (active metabolite): 11 ± 2 hours. Steady-state half-life of the combined active moiety (venlafaxine + ODV) is approximately 11 hours, supporting twice-daily dosing. |
| Protein binding | Venlafaxine: 27 ± 2% bound to plasma proteins (primarily albumin and alpha-1-acid glycoprotein). O-desmethylvenlafaxine: 30 ± 12% bound. |
| Volume of Distribution | Venlafaxine: 7.5 ± 3.7 L/kg. ODV: 5.7 ± 1.8 L/kg. Large Vd indicates extensive tissue distribution, with brain-to-plasma ratio ~2.5:1. |
| Bioavailability | Oral immediate-release: approximately 40–45% due to first-pass metabolism. Extended-release: similar absolute bioavailability (40–45%) but with reduced peak concentration fluctuations. No significant food effect on AUC. |
| Onset of Action | Oral immediate-release: antidepressant effects typically begin within 1–2 weeks, with full therapeutic benefit by 4–8 weeks. Extended-release: similar onset, but may show earlier symptom relief in some patients (e.g., anxiety reduction within 1 week). |
| Duration of Action | Immediate-release: duration of action 6–8 hours, requiring twice-daily dosing. Extended-release: duration approximately 24 hours, allowing once-daily dosing. Clinical effect persists with chronic administration; discontinuation should be gradual to avoid withdrawal symptoms. |
| Molecular Weight | 313.87 |
Initial dose 75 mg/day PO divided into 2-3 doses; may increase by 75 mg/day every 4 days to max 225 mg/day; severe depression: 150-225 mg/day; extended-release: 37.5-75 mg PO once daily, titrate up to 225 mg once daily.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | CrCl 30-50 mL/min: reduce total daily dose by 25-50%; CrCl <30 mL/min: reduce by 50% and administer once daily; hemodialysis: reduce by 50% and give after dialysis. |
| Liver impairment | Child-Pugh Class A (mild): reduce dose by 50%; Child-Pugh Class B (moderate): reduce dose by 50%; Child-Pugh Class C (severe): not recommended. |
| Pediatric use | Children and adolescents (7-17 years): initial 37.5 mg PO once daily for 1 week, then increase to 75 mg once daily; maximum 112.5 mg/day for <55 kg, 150 mg/day for ≥55 kg. |
| Geriatric use | Elderly: 25-50 mg/day PO in 2-3 divided doses; extended-release: 37.5 mg PO once daily; increase slowly to 150 mg/day max; monitor for hyponatremia and QT prolongation. |
| 1st trimester | Epidemiological data suggest an increased risk of cardiovascular malformations, particularly ventricular septal defects, with first-trimester exposure. Use only if potential benefit justifies risk. |
| 2nd trimester | Monitor for maternal and fetal effects. May increase risk of preterm birth and low birth weight. Consider dose adjustment due to increased clearance. |
| 3rd trimester | Risk of persistent pulmonary hypertension of the newborn (PPHN) and neonatal withdrawal syndrome (including CNS irritability, respiratory distress, feeding difficulties). Taper before delivery 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; cord blood concentrations are approximately 0.5-1 times maternal plasma levels. Active metabolite also crosses. |
■ FDA Black Box Warning
Antidepressants increased the risk of suicidal thinking and behavior (suicidality) in short-term studies in children, adolescents, and young adults with major depressive disorder and other psychiatric disorders. Venlafaxine is not approved for use in pediatric patients except for pediatric patients with major depressive disorder and generalized anxiety disorder.
| Common Effects | Nausea Vomiting Dizziness Insomnia difficulty in sleeping Decreased appetite Anxiety Constipation Increased sweating Sexual dysfunction |
| Serious Effects |
Concomitant use with monoamine oxidase inhibitors (MAOIs) or within 14 days of MAOI discontinuationHypersensitivity to venlafaxine or any component of the formulationUse of linezolid or intravenous methylene blue (risk of serotonin syndrome)
| Precautions | Clinical worsening and suicide risk: monitor for worsening and emergence of suicidal thoughts/behaviors, Serotonin syndrome: risk especially with concomitant serotonergic drugs, Elevated blood pressure: dose-dependent increase, monitor regularly, Angle-closure glaucoma: may precipitate an attack, Activation of mania/hypomania, Seizure: use with caution in patients with seizure disorder, Abrupt discontinuation: withdrawal symptoms (dizziness, insomnia, nausea, headache), Hepatic/renal impairment: dose adjustment required, Hyponatremia: risk in elderly or volume-depleted patients |
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| Breastfeeding | Venlafaxine and its active metabolite O-desmethylvenlafaxine are excreted into breast milk in small amounts; the estimated infant dose is <10% of maternal weight-adjusted dose. Cases of irritability and poor feeding in infants have been reported. Weigh benefits against risks; monitor infant for sedation, poor weight gain, and feeding difficulty. Preferred alternatives with lower infant exposure exist (e.g., sertraline). |
| Lactation Rating | L2 (Probably Compatible) – Limited human data suggest minimal risk. |
| Teratogenic Risk | Venlafaxine crosses the placenta. First trimester: Observational studies suggest a small increased risk of congenital cardiac defects (e.g., ventricular septal defect) with use, particularly at higher doses. Second trimester: Risk appears low; no specific malformations consistently reported. Third trimester: Exposure may increase risk of persistent pulmonary hypertension of the newborn (PPHN) and neonatal adaptation syndrome (respiratory distress, feeding difficulties, jitteriness, seizures, hypoglycemia). Overall, absolute risks are low; consider risk-benefit. |
| Fetal Monitoring | Monitor maternal blood pressure regularly due to dose-dependent hypertension risk. Assess for signs of serotonin syndrome (e.g., hyperthermia, rigidity, autonomic instability). Fetal monitoring: Standard prenatal care; consider third-trimester ultrasound if late exposure to assess for growth restriction. Neonatal monitoring after delivery for adaptation syndrome (especially if used near term), including respiratory status, feeding, and neurological behavior for at least 48 hours. |
| Fertility Effects | Venlafaxine may cause sexual dysfunction (e.g., decreased libido, erectile dysfunction, delayed orgasm) in both men and women, potentially affecting fertility. Animal studies show no major impairment of fertility at clinically relevant doses. Human data are limited; inconclusive evidence of reversible effects on spermatogenesis or ovarian function. |
| Food/Dietary | Avoid alcohol, which may increase CNS depression. No significant food interactions; can be taken with or without food, though taking with food may reduce gastrointestinal side effects. Grapefruit juice has no known interaction. |
| Clinical Pearls | Monitor for dose-dependent hypertension; sustained increases in blood pressure may require dose reduction or discontinuation. Withdrawal syndrome is common upon abrupt discontinuation; taper by 75 mg per week. Venlafaxine has a dual mechanism (SNRI) and may be more effective for severe depression or treatment-resistant cases. Use with caution in patients with seizure disorders or history of mania. Check baseline blood pressure and repeat after dose escalation. |
| Patient Advice | Take with food to reduce nausea. · Avoid abrupt discontinuation; taper under medical supervision to prevent withdrawal symptoms (dizziness, nausea, headache). · May cause drowsiness or dizziness; avoid driving until you know how you react. · Report any suicidal thoughts, especially at treatment initiation or dose changes. · Notify prescriber if you experience chest pain, shortness of breath, or severe headache (signs of hypertension). · Allow 4-6 weeks for full therapeutic effect. |