EFFEXOR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for EFFEXOR (EFFEXOR).
Inhibits serotonin and norepinephrine reuptake by blocking the serotonin transporter (SERT) and norepinephrine transporter (NET), increasing extracellular concentrations of serotonin and norepinephrine in the CNS.
| Metabolism | Primarily metabolized by CYP2D6 to O-desmethylvenlafaxine (active metabolite). Also metabolized by CYP3A4. Minor pathways via CYP2C19 and CYP2C9. |
| Excretion | Primarily renal (≈87% of dose eliminated in urine), with approximately 29% as unchanged venlafaxine, 26% as unconjugated O-desmethylvenlafaxine (ODV), and the remainder as other metabolites. Fecal elimination accounts for <10%. Biliary excretion is negligible. |
| Half-life | Venlafaxine: ~5 ± 2 hours; ODV (active metabolite): ~11 ± 2 hours. At steady state, effective half-life for total active moiety (venlafaxine + ODV) is ~11 hours. Clinical context: requires twice-daily dosing for immediate-release; extended-release formulations allow once-daily dosing. |
| Protein binding | Venlafaxine: 27 ± 2% bound, primarily to albumin and α1-acid glycoprotein. ODV: approximately 30% bound. Binding is independent of drug concentration. |
| Volume of Distribution | Venlafaxine: Vd ≈ 6–7 L/kg, indicating extensive distribution into tissues; ODV: Vd ≈ 4 L/kg. Large Vd suggests significant extravascular binding and slow tissue redistribution. |
| Bioavailability | Oral immediate-release: absolute bioavailability ≈ 40–45% (due to first-pass metabolism). Extended-release: bioavailability approximately 100% relative to immediate-release. Food has minimal effect on absorption time but not extent. |
| Onset of Action | Oral immediate-release: antidepressant effect typically begins within 1–2 weeks, with full response at 4–8 weeks. Onset of anxiolytic effect may be as early as 1 week. Extended-release: similar timeline. No parenteral route available. |
| Duration of Action | Plasma levels of active moiety persist for approximately 24 hours with extended-release formulation, supporting once-daily dosing. Clinical effect duration is continuous during chronic therapy; after discontinuation, withdrawal symptoms may occur due to short half-life. |
| Molecular Weight | 277.4 |
Initial: 75 mg/day PO in 2-3 divided doses; may increase by 75 mg/day increments at intervals of 4 days or more; max 375 mg/day. Extended-release: initial 37.5-75 mg PO once daily, titrate up to max 225 mg/day.
| Dosage form | TABLET |
| Renal impairment | GFR 10-29 mL/min: reduce dose by 50%; GFR <10 mL/min: avoid use (or use 50% reduction if hemodialysis). |
| Liver impairment | Child-Pugh A: 50% reduction of usual dose; Child-Pugh B: 50% reduction; Child-Pugh C: limited data, use with caution and likely 50% reduction. |
| Pediatric use | Initial: 37.5 mg PO once daily (extended-release) for 1 week, then increase to 75 mg once daily; max 225 mg daily. Weight-based not typically used; dosing per published guidelines. |
| Geriatric use | Initial dose 37.5 mg PO once daily (extended-release); titrate slowly; max 150 mg/day due to increased sensitivity and risk of hyponatremia. |
| 1st trimester | Risk of persistent pulmonary hypertension of the newborn (PPHN) and cardiac malformations; use only if potential benefit outweighs risk. May increase risk of spontaneous abortion. |
| 2nd trimester | Monitor fetal growth; risk of preterm delivery and low birth weight. Consider dose adjustment due to increased clearance. |
| 3rd trimester | Risk of neonatal adaptation syndrome (respiratory distress, feeding difficulties, irritability); taper before delivery if possible. Avoid abrupt discontinuation. |
Clinical note
Comprehensive clinical and safety monograph for EFFEXOR (EFFEXOR).
| Placental transfer | Venlafaxine crosses the placenta; umbilical cord plasma concentrations are approximately 70-100% of maternal plasma levels. Active metabolite desvenlafaxine also crosses. |
| Breastfeeding | Limited data; venlafaxine and desvenlafaxine are excreted into breast milk in low to moderate levels. Relative infant dose is approximately 6-9% of weight-adjusted maternal dose. Monitor infant for irritability, poor feeding, and sedation. Benefits of breastfeeding generally outweigh risks. |
■ FDA Black Box Warning
Suicidality and Antidepressant Drugs: Antidepressants increased the risk of suicidal thinking and behavior in children, adolescents, and young adults in short-term studies.
| Serious Effects |
Concurrent use with MAOIs or within 14 days of MAOI discontinuationHypersensitivity to venlafaxine or any excipientSerotonin syndrome risk with other serotonergic drugsUncontrolled narrow-angle glaucoma
| Precautions | Clinical worsening and suicide risk, Serotonin syndrome, Elevated blood pressure, Increased risk of bleeding (especially with NSAIDs/aspirin), Activation of mania/hypomania, Angle-closure glaucoma, Sexual dysfunction, Weight changes (increase in adults, decrease in children), Discontinuation syndrome (avoid abrupt cessation), Hepatic/renal impairment (dose adjustment needed), Mydriasis, Hyponatremia/SIADH, Pregnancy (third trimester: complications; avoid unless necessary) |
| Food/Dietary | No specific food interactions are documented; however, grapefruit juice may increase venlafaxine levels via CYP3A4 inhibition, though clinical significance is low. Avoid alcohol consumption as it may potentiate central nervous system depression. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | First trimester: Increased risk of cardiac malformations (e.g., ventricular septal defects), odds ratio ~1.7. Third trimester: Risk of persistent pulmonary hypertension of the newborn (PPHN), odds ratio ~2.1; also, neonatal adaptation syndrome (e.g., respiratory distress, jitteriness) with late exposure. |
| Fetal Monitoring | Fetal echocardiography at 18–22 weeks for cardiac defects if exposed in first trimester; neonatal monitoring for adaptation symptoms (respiratory, feeding, agitation) for 48–72 hours post-delivery. |
| Fertility Effects | Animal studies show no impairment; human data limited. May cause reversible sexual dysfunction (e.g., ejaculatory delay) but no evidence of reduced fertility. |
| Clinical Pearls | Effexor (venlafaxine) is a serotonin-norepinephrine reuptake inhibitor (SNRI) with a short half-life; abrupt discontinuation can cause withdrawal symptoms, so taper gradually. Monitor blood pressure regularly as it can cause sustained hypertension, especially at doses >150 mg/day. It is effective for generalized anxiety disorder and major depressive disorder, and may be considered for off-label use in hot flashes or neuropathic pain. Onset of therapeutic effect may take 2-4 weeks; inform patients to not discontinue abruptly. |
| Patient Advice | Take Effexor exactly as prescribed; do not stop suddenly without consulting your doctor, as withdrawal symptoms like dizziness, nausea, headache, and irritability may occur. · Swallow capsules whole; do not crush, chew, or sprinkle contents, especially the extended-release formulation. · If you miss a dose, take it as soon as you remember unless it is close to your next dose; do not double up. · Avoid alcohol while taking Effexor, as it may worsen side effects like drowsiness and dizziness. · Report any signs of high blood pressure such as severe headache, blurred vision, or chest pain to your doctor promptly. · It may take several weeks to feel the full benefit; do not stop if you don't feel immediate improvement. · Do not use Effexor with MAO inhibitors or within 14 days of stopping an MAOI, as it can cause a dangerous serotonin syndrome. · If you become pregnant or plan to become pregnant, discuss risks with your doctor, especially in the third trimester. |