Clozapine treatment in polydipsia and intermittent hyponatremia

Recent case reports indicate that clozapine treatment diminishes excessive diurnal weight gain and alleviates hyponatremia observed in some chronically psychotic patients. We examined the influence of clozapine on sodium metabolism and water regulation across a group of patients with the syndrome of polydipsia and intermittent hyponatremia.

Eleven patients with treatment-resistant DSM-III-R schizophrenia or schizoaffective disorder were studied. Each had a history of repeated diurnal weight gains of greater than 10% with at least one documented bout of hyponatremia in the 6 months before clozapine treatment. We utilized a target weight protocol and serial laboratory measures to compare changes in sodium metabolism and water regulation during 26 weeks of standard antipsychotic medication and 26 weeks of clozapine treatment.

Across patients, we found significant improvement in routinely monitored 6 a.m. and 4 p.m. serum sodium, reflecting normalization of sodium metabolism. We also found that the frequency (as reflected by diurnal weight gain), severity (lowest serum sodium), and estimated quantity (calculated urine volume) of polydipsia improved across patients. Improvement in polydipsia and hyponatremia was associated with decreased necessity for monitoring and restrictive interventions, and tended to be associated with psychiatric improvement.

We found a corrective and stabilizing effect of clozapine on polydipsia and intermittent hyponatremia. Future studies need to examine the relationship of psychiatric improvement and alterations in the regulation of sodium and water physiology to our findings.