Makindo Medical Notes

💊 Venlafaxine is a serotonin–noradrenaline reuptake inhibitor (SNRI) antidepressant. It increases synaptic levels of both neurotransmitters, improving mood, concentration, and energy in depression and anxiety disorders. ⚠️ Discontinuation reactions (dizziness, “brain zaps”, irritability) occur more often with venlafaxine and paroxetine than other antidepressants — always taper gradually over weeks.

📘 About

• Always check the BNF entry here for detailed prescribing and monitoring guidance.
• Used for major depressive disorder, generalised anxiety disorder (GAD), panic disorder, and social anxiety disorder.
• Available as immediate-release (BD dosing) and modified-release (once daily) formulations — not interchangeable mg-for-mg.

⚙️ Mode of Action

• Inhibits presynaptic reuptake of serotonin (5-HT) and noradrenaline (NA).
• At low doses → mainly serotonergic; at higher doses → also noradrenergic.
• Minimal affinity for histaminergic, cholinergic, or α-adrenergic receptors → fewer antimuscarinic effects.
• Do not stop suddenly due to short half-life (≈5 hours) and high withdrawal risk.

💊 Indications & Doses

• Major depressive disorder: Start 37.5 mg twice daily; increase to 75 mg twice daily if tolerated.
• Maintenance: usually 150–225 mg/day (max 375 mg/day).
• Modified-release: 75 mg once daily → may titrate to 225 mg once daily (max 375 mg/day under specialist supervision).
• Always review blood pressure before dose escalation.

📈 Dose Range (Check BNF or Data Sheet)

🔄 Interactions

• MAOIs: contraindicated — risk of serotonin syndrome (separate by at least 14 days).
• ↑ risk of bleeding with aspirin, NSAIDs, anticoagulants (due to platelet serotonin depletion).
• Selegiline or linezolid: risk of CNS toxicity.
• May enhance warfarin effect — monitor INR if co-prescribed.

⚠️ Cautions

• Monitor for hypertension — dose-dependent blood pressure increase.
• Use cautiously in cardiac arrhythmias, recent MI, or QT-prolonging drugs.
• Avoid abrupt withdrawal — taper over ≥2 weeks.
• May exacerbate anxiety transiently at initiation (start low, go slow).

🚫 Contraindications

• Concurrent or recent (within 14 days) MAOI use.
• Uncontrolled hypertension or serious cardiac disease (relative).
• Severe hepatic or renal impairment (dose adjustment required).

💥 Adverse Effects

• 💧 Nausea, vomiting, constipation, dry mouth.
• ❤️ Palpitations, hypertension, dizziness, headache.
• 🧠 Insomnia, anxiety, agitation, sexual dysfunction.
• ⚡ Withdrawal symptoms: dizziness, paraesthesia, “electric shock” sensations, vivid dreams.
• Rare: hyponatraemia (SIADH), seizures, mania, or angle-closure glaucoma.

🧠 Teaching Note

Venlafaxine bridges the gap between SSRIs and tricyclics — useful when SSRIs fail. It highlights the importance of neurotransmitter selectivity: serotonin for mood, noradrenaline for energy and drive. Always counsel patients about gradual withdrawal and blood pressure monitoring. If discontinuation symptoms occur, reinstate the previous dose and taper more slowly.

📚 References

• BNF: Venlafaxine
• NICE NG222: Depression in adults (2024)
• NICE CKS: Generalised anxiety disorder

🕓 Revisions

• 2025-10 — Expanded and annotated by Dr O’Kane (Makindo edition).