For patients with relatively asymptomatic chronic hyponatremia, medical management becomes more challenging because these individuals may be seen in the ambulatory setting and not in an inpatient facility. Restricting fluid intake to low levels is difficult due to poor patient compliance and inadequate understanding of which fluids contain water. Therefore, turning to medications to force water loss is a viable option. Urea causes an osmotic diuresis, and urea tablets (not available in the United States) have been used in Belgium to treat SIADH; however, their bitter taste and pill burden result in poor patient acceptance.[12,13] Similarly, sodium chloride tablets and furosemide have been used in the ambulatory setting, causing a natriuresis/diuresis; again, their large pill burden and sour taste contribute to poor patient compliance. Demeclocycline causes reversible diabetes insipidus and has been used for years to treat SIADH, although side effects such as photosensitivity, allergic reactions, or liver or kidney toxicity can limit its use.[14,15]
The "vaptans," such as tolvaptan, have emerged as a well-tolerated option to treat SIADH by blocking the effects of antidiuretic hormone.[16,17] Tolvaptan has had much clinical use since it was approved by the US Food and Drug Administration (FDA) in 2009 for the treatment of hyponatremia caused by SIADH or by heart failure, and this drug is available for the treatment of SIADH in selected cases. The orally available form of tolvaptan has been used successfully for the treatment of hyponatremia caused by SIADH in a series of 10 patients with small cell lung cancer. This is a viable option, but it is expensive and may cause liver injury in those on the medication for more than a month. Tolvaptan is not recommended for more than 30-day use because of potential liver toxicity; however, one report described once-weekly safe use at a low dose for a prolonged period in the outpatient setting in an elderly patient with symptomatic chronic hyponatremia due to SIADH. More likely, a combination of oral agents is needed to manage chronic SIADH, with water restriction and patient education.
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