Clozapine usage increases the incidence of pneumonia compared with risperidone and the general population: a retrospective comparison of clozapine, risperidone, and the general population in a single hospital over 25 months.

The aim of this study was to determine whether the incidence of pneumonia in patients taking clozapine was more frequent compared with those taking risperidone or no atypical antipsychotics at all before admission to a tertiary care medical center. This was a retrospective, case-matched study of 465 general medicine patients over a 25 month period from 1 July 2010 to 31 July 2012. Detailed electronic medical records were analyzed to explore the association between the use of two atypical antipsychotics and incidence of pneumonia. Of the 155 patients in the clozapine group, 54 (34.8%) had documented pneumonia compared with 22 (14.2%) in the risperidone group and 18 (11.6%) in the general population group. Clozapine, when compared with the untreated general population, was associated with an increased risk of pneumonia (odds ratio=4.07; 95% confidence interval=2.25-7.36). There was, however, no significant increase in the risk of pneumonia associated with the use of risperidone (odds ratio=1.26; 95% confidence interval=0.65-2.45). Clozapine use is associated with increased risk of pneumonia that may be related to immunologic factors or side effects of sedation and drooling that make aspiration more likely, although causative mechanisms require further investigation. These findings suggest that providers should use added caution in choosing candidates for clozapine therapy.