Tolvaptan Versus Fluid Restriction in the Treatment of Hyponatremia Resulting from SIADH Following Pituitary Surgery

Context. The relevance of hyponatremia has been acknowledged by guidelines from the United States (2013) and Europe (2014). However, treatment recommendations differ due to limited evidence. Objective. In hyponatremia following pituitary surgery-caused by the syndrome of inappropriate antidiuretic hormone (SIADH) secretion-we compared fluid restriction with the pharmacological increase of water excretion by blocking the vasopressin 2 receptors with tolvaptan at a low and a moderate dose. Design. Prospective observational study. Setting. Neurosurgical Department of a University hospital with more than 200 surgical pituitary procedures per year. Patients. Patients undergoing pituitary surgery and developing serum sodium below 136 mmol/L. The diagnosis of SIADII was established by euvolemia (daily measurement of body weight and fluid balance), inappropriately concentrated urine (specific gravity), and exclusion of adrenocorticotropic and thyroid-stimulating hormone deficiency. Intervention. Patients were treated with fluid restriction On = 40) or tolvaptan at 3.75 (n = 38) or 7.5 mg (n = 48). Main Outcome Measures. Treatment efficacy was assessed by the duration of hyponatremia, sodium nadir, and length of hospitalization. Safety was established by a sodium increment below 10 mmol/L per day and exclusion of side effects. Results. Treatment with 7.5 mg of tolvaptan resulted in a significant attenuation of hyponatremia and in a significant overcorrection of serum sodium in 30% of patients. The duration of hospitalization did not differ between treatment groups. Conclusions. Tolvaptan at a moderate dose is more effective than fluid restriction in the treatment of SIADH. Overcorrection of serum sodium may be a side effect of tolvaptan even at low doses. (C) Endocrine Society 2020.