Urea for hyponatraemia due to the syndrome of inappropriate antidiuretic hormone secretion.

Background: Hyponatraemia due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) can pose a therapeutic challenge. After fluid restriction, urea is recommended as a second-line treatment by Dutch and European treatment guidelines. Data on this practice are still scarce. We introduced urea for the treatment of SIADH in our hospital and prospectively collected data on its effectiveness and tolerability.

Methods: In hospitalised patients with a serum sodium level ≤ 129 mmol/l due to SIADH, urea in a dosage of 0.25-0.50 g/kg/day was indicated if prescribed fluid restriction had no effect or could not be applied. Measurement of serum sodium was performed at baseline, after the first and second day of urea therapy and at the end of the first inpatient treatment episode (EIT). The primary outcomes were normonatraemia (serum sodium level 135-145 mmol/l) at EIT and discontinuation of urea due to side effects.

Results: Thirteen patients were treated with urea over a median of 5 days (range 2-10 days). The median serum sodium level at baseline was 124 mmol/l (IQR 122-128), which increased to 128 mmol/l (IQR 123-130) (p = 0.003) after the first dose of urea and to 130 mmol/l (IQR 127-133) (p = 0.002) after the second dose of urea. Normonatraemia at EIT was observed in 8 (62%) patients. Seven (54%) patients reported distaste. In one of these patients, urea was discontinued because of nausea. Overcorrection was not observed.

Conclusion: Our data show that urea is an effective treatment for hospitalised patients with SIADH. Distaste was a frequent side effect, but usually did not lead to early treatment discontinuation.