To compare the rate of hospitalizations for pneumonia in patients with a psychotic or bipolar disorder who were prescribed 1 of 4 second-generation antipsychotics prior to admission.
This retrospective cohort study included patients who were medically admitted for pneumonia to a 2,059-bed academic medical center or its associated health system hospital. Medical records of 872 admissions from November 1, 2016 to December 15, 2018, were included for all adults with a diagnosis of schizophrenia, schizoaffective disorder, or bipolar disorder prescribed clozapine, olanzapine, quetiapine, or risperidone prior to admission.
There was no significantly increased risk of pneumonia for patients taking olanzapine (odds ratio [OR] = 1.08, 95% CI, 0.48-2.41) or quetiapine (OR = 0.97, 95% CI, 0.42-2.25) prior to admission compared to risperidone. When controlling for various factors, treatment with a combination of antipsychotics including clozapine (OR = 2.28, 95% CI, 1.13-4.62, P = .022) and clozapine alone (OR = 2.37, 95% CI, 1.30-4.32, P = .005) was associated with an increased risk of pneumonia-related hospitalization compared to treatment with risperidone, olanzapine, or quetiapine alone.
The findings of this study in combination with other published literature support an association of an increased risk of pneumonia with the use of clozapine, although this cannot be interpreted as causal. These data show that use of clozapine alone or in combination with other antipsychotics significantly increases risk of pneumonia, although this finding cannot be deemed causal due to study design.

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