Treatment of the Polydipsia-Hyponatremia Syndrome With Urea

Objective: The polydipsia-hyponatremia syndrome is difficult to control in patients with severe mental illness, and there is no established effective therapeutic approach. We investigate the effect of oral daily intake of large amounts of urea to prevent hyponatremic episodes.

Method: Seven patients were treated during 4 to 18 months with urea (0.3-0.9 g/kg/day). Five of these patients had schizophrenia. Body weight variation between morning and evening was determined before and during the course of therapy in 5 patients. The dose of urea was increased if morning serum sodium level (SNa) was lower than 132 mmol/L.

Results: Urea therapy increased mean ± SD morning SNa (from 127.5 ± 3.4 mmol/L before initiation of urea treatment to 136.5 ± 2.4 mmol/L during the second month of urea treatment; p < .01) and mean ± SD urine osmolality (from 86 ± 39 mOsm/kg H₂O to 159 ± 58 mOsm/kg H₂O; p < .05), probably without changes in water intake or urine volume excretion as attested by the level of urinary creatinine concentration. Mean±SD body weight variation decreased from 4.5% ± 1.0% before initiation of urea treatment to 2.8% ± 1.0% during the second month of urea treatment (p < .05). Two patients stopped urea treatment after 1 year and subsequently developed symptomatic hyponatremia.

Conclusion: These preliminary data show that urea appears to be an effective therapeutic approach for the polydipsia-hyponatremia syndrome.