Management of Drug-Induced SIADH in an Elderly Female on Escitalopram
Immediate Action Required
Discontinue escitalopram immediately, as this is the most likely cause of SIADH-induced hyponatremia in this patient, and initiate fluid restriction to 1 L/day. 1, 2
Your patient's laboratory findings are diagnostic for SIADH:
- Hyponatremia (131 mmol/L)
- Elevated urine osmolality (888 mOsm/kg) indicating inability to dilute urine
- High urine sodium (116 mmol/L) indicating renal sodium wasting
- Low serum uric acid (3.4 mg/dL, which has 73-100% positive predictive value for SIADH) 1
- Normal TSH (1.090) ruling out hypothyroidism 1
- Serum osmolality 290 mOsm/kg (low-normal to slightly low) 1
Primary Treatment Strategy
1. Drug Discontinuation
Stop escitalopram immediately. 2, 3, 4 SSRIs, particularly escitalopram, are well-documented causes of SIADH, especially in elderly patients. 2, 3, 4 The FDA label specifically warns that hyponatremia may occur with escitalopram and is often due to SIADH, with elderly patients at particularly high risk. 2
2. Fluid Restriction
Implement strict fluid restriction to 1000 mL (1 L) per day. 1, 5, 6 This is the cornerstone of SIADH treatment for mild to moderate symptomatic cases. 1, 5
3. Sodium Supplementation (if needed)
If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily. 1 This provides additional sodium without increasing fluid intake.
Monitoring Protocol
Check serum sodium every 24 hours initially, then adjust frequency based on response. 1 For this patient with sodium of 131 mmol/L (mild hyponatremia), daily monitoring is appropriate initially. 1
Target correction rate: Do not exceed 8 mmol/L increase in 24 hours. 1, 7 Even though this patient has mild hyponatremia, overcorrection risks osmotic demyelination syndrome. 1, 7
Expected Clinical Course
Hyponatremia should improve within 2-14 days after discontinuing escitalopram. 6, 3, 4 Case reports show normalization typically occurs within 4-14 days with drug discontinuation and fluid restriction. 6, 3, 4
Assessment of Symptom Severity
Evaluate for symptoms of hyponatremia:
- Mild symptoms: Headache, difficulty concentrating, memory impairment, confusion, weakness, unsteadiness 2
- Severe symptoms: Seizures, coma, altered mental status 1, 2
If the patient has severe symptoms (seizures, altered mental status), administer 3% hypertonic saline with target correction of 6 mmol/L over 6 hours or until symptoms resolve. 1 However, at sodium 131 mmol/L, severe symptoms are unlikely unless there was rapid onset. 1
Volume Status Confirmation
Confirm euvolemia clinically: No edema, no orthostatic hypotension, normal skin turgor, moist mucous membranes. 1 This distinguishes SIADH from hypovolemic or hypervolemic causes of hyponatremia. 1
Critical Pitfalls to Avoid
Do NOT administer normal saline. 1, 6 Normal saline will worsen hyponatremia in SIADH because the patient cannot excrete free water appropriately. 1, 6 One case report specifically documented that hyponatremia did not improve with isotonic saline but only with fluid restriction. 6
Do NOT ignore mild hyponatremia (130-135 mmol/L). 1 Even mild hyponatremia increases fall risk (21% vs 5% in normonatremic patients) and mortality (60-fold increase). 1
Do NOT correct too rapidly. 1, 7 Maximum correction is 8 mmol/L in 24 hours; elderly patients and those with chronic hyponatremia are at highest risk for osmotic demyelination syndrome. 1, 7
Alternative Antidepressant Considerations
When restarting antidepressant therapy, consider alternatives with lower SIADH risk and monitor sodium closely. 2, 3, 4 All SSRIs carry some risk of hyponatremia, particularly in elderly patients. 2, 3, 4 If escitalopram must be restarted, do so only after sodium normalizes and with close monitoring. 2