From the Guidelines
The management of Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) should prioritize treating the underlying cause while addressing hyponatremia through fluid restriction and pharmacological interventions, with a focus on maintaining serum sodium levels between 130-135 mEq/L. The first-line treatment involves restricting fluid intake to less than 1 L/day, which creates a negative water balance by limiting free water intake 1. For acute symptomatic hyponatremia (serum sodium <120 mEq/L with neurological symptoms), hypertonic 3% saline should be administered intravenously at 1-2 mL/kg/hour with careful monitoring to raise sodium by 4-6 mEq/L in the first 24 hours, avoiding correction rates exceeding 8-10 mEq/L/day to prevent osmotic demyelination syndrome 1. Some key points to consider in the management of SIADH include:
- Restricting fluid intake to less than 1 L/day
- Using hypertonic 3% saline for acute symptomatic hyponatremia
- Considering pharmacological options such as tolvaptan, demeclocycline, or urea for chronic or less severe cases
- Monitoring treatment effectiveness through regular serum sodium measurements
- Addressing the underlying etiology, which may include malignancies, pulmonary disorders, CNS diseases, or medication effects It is also important to note that vaptans, such as tolvaptan, have been shown to be effective in improving serum sodium concentration in conditions associated with high vasopressin levels, such as SIADH 1. The use of tolvaptan, starting at 15 mg daily and titrating up to 60 mg if needed, is a recommended pharmacological option for the management of SIADH, as it promotes aquaresis and can help improve serum sodium concentration.
From the FDA Drug Label
Tolvaptan tablets are indicated for the treatment of clinically significant hypervolemic and euvolemic hyponatremia (serum sodium <125 mEq/L or less marked hyponatremia that is symptomatic and has resisted correction with fluid restriction), including patients with heart failure and Syndrome of Inappropriate Antidiuretic Hormone (SIADH) The usual starting dose for tolvaptan tablets is 15 mg administered once daily without regard to meals. Increase the dose to 30 mg once daily, after at least 24 hours, to a maximum of 60 mg once daily, as needed to achieve the desired level of serum sodium.
The management of SIADH includes the use of tolvaptan, a medication that helps to increase serum sodium levels. The recommended dosage is to start with 15 mg once daily and increase as needed to a maximum of 60 mg once daily. It is essential to monitor serum sodium levels closely and avoid too rapid correction to prevent serious neurologic sequelae.
- Key considerations:
- Initiate and re-initiate tolvaptan in a hospital setting to monitor serum sodium levels.
- Avoid fluid restriction during the first 24 hours of therapy.
- Monitor for changes in serum electrolytes and volume status.
- Do not administer tolvaptan for more than 30 days to minimize the risk of liver injury 2.
From the Research
Management of SIADH
The management of Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) involves treating hyponatremia to cure symptoms. The following are some of the therapeutic modalities used:
- Nonspecific measures and means, such as fluid restriction, hypertonic saline, urea, and demeclocycline 3
- Vasopressin receptor antagonists, called vaptans, which have been introduced as specific and direct therapy of SIADH 3, 4, 5, 6, 7
Treatment Options
Some of the treatment options for SIADH include:
- Fluid restriction, which is commonly used to treat SIADH 3
- Hypertonic saline, which can be used to rapidly correct hyponatremia 3
- Urea, which can be used to increase serum sodium levels 3
- Demeclocycline, which can be used to treat SIADH 3
- Tolvaptan, a selective vasopressin V2-receptor antagonist, which has been shown to be effective in treating SIADH 4, 5, 6, 7
Important Considerations
When treating SIADH, it is important to:
- Limit the daily increase of serum sodium to less than 8-10 mmol/liter to prevent osmotic demyelination 3
- Monitor serum sodium levels closely, especially during the first 24 hours of treatment with vaptans 3, 4
- Avoid fluid restriction during the first 24 hours of treatment with tolvaptan to prevent overly rapid correction of hyponatremia 4
- Be aware of the potential side effects of vaptans, such as thirst, polydipsia, and frequency of urination 3, 4, 6, 7