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Figure 2. When the patient is not a candidate for chemotherapy (modified from Escobar et al. [29] )

restriction refers to all administered liquids, including i.v. medication and semisolids administered in the
diet.

Fluid restriction should not be attempted if the patient’s biochemistry indicates their kidneys are unable to
eliminate free water. To ascertain response, the Furst formula can be applied.

[23]
The first approach is fluid restriction and increased salt intake in diet, applying the Furst formula :
(Urine sodium + Urine K)/Serum sodium

The result of this formula will predict whether fluid restriction will be effective for the treatment of
hypervolemic or euvolemic hyponatremia, and the threshold of the liquid restriction: (1) < 0.5: fluid
restriction of < 1000 cc/day; (2) 0.5-1: fluid restriction of < 500 cc/day; (3) > 1: fluid restriction ineffective.

In cancer patients with a high prevalence of and risk for malnutrition and the frequent need for dilution of
chemotherapy, fluid restriction is often not viable [14,19] .

[24]
Evidence in favor of the use of fluid restriction in patients with hypervolemic hyponatremia is scant .
However, its use has been incorporated into therapeutic algorithms of congestive heart failure. If there is no
[25]
response to fluid restriction, Tolvaptan could be considered .

Patients who are not candidates for chemotherapy
Supportive treatment and treatment of hyponatremia should be prioritized according to the severity of the
symptoms, rather than the level of hyponatremia per se [Figure 2].

Hyponatremia due to SIADH in cancer patients
Tolvaptan is approved for the treatment of SIADH-induced hyponatremia in adult patients [26-28] .