What is the treatment for Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)?

Treatment of Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

The first-line treatment for SIADH is fluid restriction (<1 L/day), with more aggressive interventions like hypertonic saline reserved for severe symptomatic cases. 1

Diagnosis Confirmation

Before initiating treatment, confirm SIADH diagnosis based on:

• Hyponatremia (serum sodium <134 mEq/L)
• Plasma hypoosmolality (<275 mosm/kg)
• Inappropriately high urine osmolality (>500 mosm/kg)
• Inappropriately high urinary sodium (>20 mEq/L)
• Absence of hypothyroidism, adrenal insufficiency, or volume depletion 1

Treatment Algorithm Based on Symptom Severity

Severe Symptoms (Mental status changes, seizures)

1. Transfer to ICU with close monitoring (sodium levels every 2 hours)
2. Administer 3% hypertonic saline
   • Target correction: 6 mmol/L over 6 hours or until severe symptoms resolve
   • Do not exceed total correction of 8 mmol/L in 24 hours 2
   • Calculate sodium deficit: Desired increase in Na (mEq) × (0.5 × ideal body weight)
3. Stop 3% saline when severe symptoms resolve; transition to mild symptom protocol
4. If no response, add oral sodium chloride 100 mEq TID 2

Mild Symptoms (Nausea, vomiting, headache) or Sodium <120 mmol/L

1. Fluid restriction to 1 L/day
2. Monitor sodium levels every 4 hours
3. High protein diet 2, 1

Asymptomatic with Sodium >120 mmol/L

1. Fluid restriction to 1-1.5 L/day 1, 3
2. Daily sodium monitoring
3. Salt supplementation if needed 1

Pharmacological Options

First-Line

• Fluid restriction (<1 L/day) - shown to increase sodium by approximately 4 mmol/L after 30 days in chronic SIADH 3

Second-Line (if fluid restriction fails or is poorly tolerated)

• Tolvaptan (vasopressin V2 receptor antagonist)

  • Starting dose: 15 mg once daily
  • May increase to 30 mg after 24 hours, maximum 60 mg daily
  • MUST initiate in hospital setting with close sodium monitoring
  • Do not use for more than 30 days due to risk of liver injury
  • Contraindicated in hypovolemic hyponatremia and ADPKD 4
  • Avoid rapid correction (>12 mEq/L/24 hours) to prevent osmotic demyelination 4

• Demeclocycline - can be used for chronic SIADH if fluid restriction is not tolerated 5

Important Cautions

• Avoid overcorrection of sodium levels, as it can lead to osmotic demyelination syndrome

  • Never exceed correction of 8 mmol/L in 24 hours, especially in high-risk patients (liver disease, alcoholism, malnutrition) 1
  • Correction of 6 mmol/L in first 6 hours, then no more than 2 mmol/L in following 18 hours 2

• Do not restrict fluids in cerebral salt wasting (differentiate from SIADH)

  • Cerebral salt wasting presents with hypovolemia, while SIADH is euvolemic 6

• Patients should be allowed to drink in response to thirst during the first 24 hours of tolvaptan therapy 4

Monitoring

• Monitor serum sodium every 2-4 hours initially in severe cases
• For chronic management, check sodium levels daily until stable
• Evaluate for symptoms of electrolyte imbalance regularly 1

Treatment Duration

• Continue treatment until underlying cause is corrected
• For chronic SIADH where the cause cannot be eliminated, long-term fluid restriction or pharmacologic therapy may be necessary 5, 7

By following this structured approach based on symptom severity, SIADH can be effectively managed while minimizing the risk of complications from overly rapid sodium correction.