TREATMENT Olanzapine and fluid restriction
In the psychiatric unit, Mr. F is restarted on olanzapine, but not on perphenazine due to anticholinergic effects and not on propranolol due to continued orthostatic hypotension. Five days later, he is at his baseline level of functioning with residual psychosis. His fluid intake is restricted to <1.5 L per day and he is easily compliant.
Mr. F’s mother is comfortable with his discharge home on a regimen of olanzapine, 25 mg/d, and the team discusses the fluid restrictions with her. The treatment team suggests initiating an LAI before Mr. F is discharged, but this is not pursued because his mother thinks he is doing well with the oral medication. She wants to monitor him with the medication changes in the clinic before pursuing an LAI; however, she is open to it in the future.
The authors’ observations
Approximately 20% of patients with schizophrenia may experience psychogenic polydipsia.4,5 The cause of psychogenic polydipsia in patients with serious mental illness is multifactorial. It may stem from malfunction of the hypothalamic-pituitary axis, which leads to alterations in antidiuretic hormone secretion and function.4-6
Mr. F’s case highlights several challenges associated with treating psychogenic polydipsia in patients with serious mental illness. Antipsychotics with high dopamine affinity, such as risperidone and haloperidol, may increase the risk of psychogenic polydipsia, while antipsychotics with lower dopamine affinity, such as clozapine, may decrease the occurrence.5 Antipsychotics block postsynaptic dopamine receptors, which can induce supersensitivity by increasing presynaptic dopamine release in the hypothalamic areas, where thirst regulation occurs. This increase in dopamine leads to increased thirst drive and fluid intake.3
Quetiapine or clozapine may have been a better antipsychotic choice because these agents have lower D2 receptor affinity, whereas olanzapine has intermediate binding to D2 receptors.6,7 However, quetiapine and clozapine are more strongly associated with orthostasis, which was a concern during Mr. F’s hospitalization. The weekly laboratory testing required with clozapine use would have been an unfeasible burden for Mr. F because he lived in a rural environment. Perphenazine was not continued due to higher D2 affinity and anticholinergic effects, which can increase thirst.6
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