Clozapine restores water balance in schizophrenic patients with polydipsia-hyponatremia syndrome.

Hyponatremia/hypoosmolemia causes marked morbidity and prolongs hospital stays in a significant subset of schizophrenic patients. Case reports with methodological limitations suggest clozapine ameliorates this water imbalance. To more conclusively assess this possibility, we completed a 24-week open-label study in 8 male polydipsic hypoosmolemic schizophrenic inpatients. Subjects were treated initially for 6 weeks with a conventional neuroleptic, which was replaced by 300, 600, and 900 (if tolerated) mg/day of clozapine for sequential 6-week periods. On clozapine, mean plasma osmolality rose an average of 15.2 mosm/kg (95% CI: 5.5-25.0). Dosage of 300 mg/day of clozapine was sufficient to normalize plasma osmolality and was generally well tolerated. Clozapine appears to be the first effective pharmacotherapy for severe water imbalance in schizophrenia.