Endocrine Abstracts

Introduction: There are several endocrine causes of hyponatremia. SIADH is perhaps the most challenging, as patients do not always respond to initial correction measures and pharmacological treatment options are scarce. Urea is a viable option, but not commonly used.

Methods: Analysis of patients with SIADH-induced hyponatremia (<135mEq/l) treated with urea per os in the Portuguese Institute of Oncology of Porto between August 2021 and October 2021.

Results: Seventeen patients were included, with median age of 61 (19,5) years. In 15 patients, SIADH had a neoplastic etiology, mostly in the context of small cell lung carcinoma, and in 2, several factors, including pharmacological ones, contributed to the syndrome. Serum sodium nadir was 117 (11) mEq/l. Most patients received treatment with 0,9% saline, hypertonic saline, water restriction and/or increased protein/salt consumption before starting urea. They presented a pre-therapeutic sodium of 123 (5,5) mEq/l, plasmatic and urinary osmolality of 261±9,74 and 558 (263,5) mOsm/kg, respectively, and urinary sodium of 97 (102). Urea was started orally at a dose of 10mg bid. Fourteen out of 17 patients were reevaluated 48-72h later, showing a statistically significant rise in plasma sodium [127 (4,5) (P=0,009)]. Patients continued treatment for a median of 96 (196) days, and plasma sodium continued to improve until their last bloodwork [sodium 134 (7) mEq/l; P<0,001)]. There was no clinically relevant change in renal function [(pre and post treatment creatinine 0,55±0,17 vs. 0,65±0,2, respectively (P=0,007)], and no other adverse effects were recorded.

Conclusions: Urea appears to be a safe and effective treatment for patients with SIADH-induced hyponatremia refractory to the usual initial correction measures.