Hyponatremia and Antidepressants: A Must-Know Topic for PLAB 2
- Ann Augustin
- Aug 1
- 2 min read
Updated: Aug 2
Antidepressants are commonly prescribed in UK primary care, and understanding their side effects—especially hyponatremia—is vital for PLAB 2 candidates. This blog walks you through the key mechanisms, high-risk drugs, alternative medications, and how to counsel patients effectively.
💧 What is Hyponatremia?
Hyponatremia is a low sodium level in the blood (Na⁺ <135 mmol/L), most commonly caused by SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) in patients taking certain antidepressants.
🧪 Pathophysiology: How Antidepressants Cause
Hyponatremia
🔹 SSRIs and SNRIs:
Increase serotonin levels, which stimulate ADH release from the hypothalamus.
ADH causes water retention, diluting sodium concentration → hyponatremia.
💊 High-Risk Antidepressants
✅ SSRIs (Highest Risk):
Citalopram
Sertraline
Fluoxetine
Escitalopram
Paroxetine
⚠️ SNRIs (Moderate Risk):
Venlafaxine (notably highest risk among antidepressants)
Duloxetine
Desvenlafaxine
⚠️ TCAs (Lower Risk, but possible):
Amitriptyline
Nortriptyline
⚠️ Other antidepressants:
Mirtazapine – Low risk (preferred in hyponatremia cases)
Bupropion – Very low risk (NDRI; does not affect serotonin)
⏳ When Can It Occur?
Typically within the first 1–4 weeks, but can also occur months later.
Remain vigilant even in long-term users, especially the elderly.
⚠️ Red Flags and Symptoms:
Tiredness
Nausea
Headache
Confusion
Dizziness or unsteadiness
Seizures (in severe cases)
Always check U&Es (urea and electrolytes) in at-risk patients or those presenting with non-specific symptoms.
🩺 First-Line Management of SSRI-induced Hyponatremia:
1️⃣ Stop the offending drug (e.g., citalopram)
2️⃣ Switch to a safer alternative:
💬 PLAB 2 Communication Example
🧑⚕️ “I understand citalopram was helping your mood, and it’s concerning to hear we might need to stop it. However, it’s affected your sodium level, which could cause more serious symptoms. A safer alternative like Mirtazapine or Buropion can still help your mood and is much less likely to affect your salt balance. We’ll monitor you closely as you make the switch.”
📚 Clinical Pearls for PLAB 2
Always think of hyponatremia in elderly patients on SSRIs/SNRIs who present with new confusion, fatigue, or falls.
Counsel empathetically when switching medications. Acknowledge the benefit the patient felt with the previous drug.
Know your alternatives and explain the rationale clearly.
Monitor sodium levels during and after switching.
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