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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for EFFEXOR (EFFEXOR).
| Breastfeeding | Excreted into breast milk; M/P ratio ~0.7. Relative infant dose ~6.8%. Cases of irritability and poor feeding reported. Weigh benefits against potential risks; consider monitoring infant for sedation and adequate weight gain. |
| 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. |
■ 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 |
["Concomitant use with MAOIs or within 14 days of MAOI use","Known hypersensitivity to venlafaxine or any component","Uncontrolled 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)"] |
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| 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. |