Endocrine Abstracts

Introduction: The most common cause of hyponatraemia is the syndrome of inappropriate antidiuretic hormone (SIADH). The diagnosis typically requires hyponatraemia in the setting of reduced serum osmolality, inappropriately concentrated urine with normal sodium excretion levels, and the absence of interfering medications, hypothyroidism and adrenal insufficiency. Unless hypertonic saline is indicated for acute onset profound hyponatraemia and/or with severe symptoms, the mainstay of management has traditionally been fluid restriction, a treatment often difficult to implement practically and effective in less than 50% of patients. Recent European and American guidelines differ in their approach to second-line management. Urea has been used for the treatment of SIADH since the 1980s but only few case reports/series have demonstrated it is an effective adjunct where fluid restriction is impractical or ineffective.

Objective: The objective of the study was to demonstrate that treatment with urea in patients with SIADH is a safe and effective alternative when fluid restriction has failed.

Methods: Treatment with urea (15 g/day) was started in all patients with biochimical diagnosis of SIADH (serum and urine natremia, plasmatic and urine osmolarity was determined) between 2016 and 2019. In all patients hypothyroidism and adrenal insufficiency was excluded. Results were analysed with SPSS v. 21.

Results: 20 Subjects (55% men) were analysed with an average age of 77.05 ± 15.4 years old, with biochemical diagnosis of SIADH. In our serie, the main cause of SIADH was drugs (50%), other causes were 25% paraneoplasia, 10% brain hemorrhage, 10% lung patology and 5% idiopathic. Initial natrium level was 124 ± 3.8 mEq/l before treatment was started, with an average plasm osmolality 269 ± 15.4 mOsm/l, urinary sodium 114 ± 98,8 mEq/l, and urinary osmolality 484.6 ± 235.56 mOsm/kg. Treatment with 15 g/day with urea was started with a median duration of 35 days, the natrium level was corrected in all patients, and it could be discontinued in 85% of them. The final average natrium level was 136.7 ± 4 mEq/l, plasm osmolality 295.25 ± 28.85 mOsm/l, urinary sodium 88.6 ± 28.7 mEq/l and urinary osmolality 528.6 ± 186.5 mOsm/kg. A rate mortality of 55% was observed, none of them due to SIADH.

Conclusions: Urea is safe and effective in fluid restriction-refractory hyponatraemia. We recommend urea with a starting dose of 15 g/day in patients with SIADH and moderate to profound hyponatraemia, as in our serie 100%, sodium levels were normalized and in 85% treatment with urea could be discontinued.