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 (1,000-1,500 mL/day) combined with adequate oral salt intake, and discontinuation of any implicated medications. 1

Diagnosis Confirmation

Before initiating treatment, confirm SIADH diagnosis with:

• Hyponatremia (serum sodium <134 mEq/L)
• Plasma hypoosmolality (<275 mOsm/kg)
• Inappropriately high urine osmolality (>500 mOsm/kg)
• Elevated urinary sodium concentration (>20 mEq/L)
• Normal adrenal and thyroid function
• Euvolemic status (normal blood pressure, no edema)

Treatment Algorithm Based on Severity

Mild to Moderate Hyponatremia (126-135 mEq/L)

• Fluid restriction (1,000-1,500 mL/day)
• Increase oral salt intake
• Monitor serum sodium levels

Moderate to Severe Hyponatremia (120-125 mEq/L)

• Stricter fluid restriction (500-1,000 mL/day)
• Consider pharmacologic therapy if fluid restriction fails:
  • Tolvaptan: Starting dose 15 mg once daily, can be titrated to 30 mg, then 60 mg once daily as needed 2
  • Urea: Effective for rapid correction of symptomatic hyponatremia 1, 3
  • Demeclocycline: Can be used if fluid restriction is not tolerated 1, 4

Severe Symptomatic Hyponatremia (<120 mEq/L with neurological symptoms)

• Hypertonic (3%) saline for immediate relief of severe symptoms (confusion, seizures) 1, 5
• Administer as 100-150 mL bolus or continuous infusion depending on symptom severity 3
• Close monitoring of serum sodium levels

Critical Safety Considerations

1. Correction Rate: Limit sodium correction to 8-10 mmol/L per 24 hours to prevent osmotic demyelination syndrome 1, 4, 5

2. Hospital Monitoring: Initiate and re-initiate tolvaptan only in a hospital setting where serum sodium can be closely monitored 2

3. Tolvaptan Monitoring: When using tolvaptan, measure serum sodium at 0,6,24, and 48 hours after initiation 4

4. Duration Limitations: Do not administer tolvaptan for more than 30 days to minimize risk of liver injury 2

5. Post-Treatment Care: After discontinuing tolvaptan, resume fluid restriction and monitor for hyponatremic relapse 2, 4

Special Considerations

• High-Risk Patients: Patients with severe malnutrition, alcoholism, or advanced liver disease require slower correction rates 2

• Fluid Restriction Failure: Nearly half of SIADH patients do not respond to fluid restriction as first-line therapy, necessitating second-line treatments 3

• Avoid Normal Saline: 0.9% saline should be avoided in SIADH as it can cause rapid fluctuations in serum sodium levels 5

• Differential Diagnosis: Rule out cerebral salt wasting syndrome, which presents similarly but requires volume replacement rather than restriction 6

By following this structured approach to SIADH treatment with careful attention to correction rates and monitoring, you can effectively manage this condition while minimizing the risk of complications.