Eosinophilic pneumonia during treatment with clozapine: reports from a retrospective case series

Clozapine is an atypical antipsychotic known to cause multiple hematologic abnormalities, most seriously agranulocytosis, but also notably eosinophilia. It is considered as an allergic reaction with a spontaneous remission, however, sometimes, it may predict subsequent major inflammatory complications. The aim of this study was to investigate the relationship between clozapine usage and drug-induced pneumonia based on characteristic respiratory symptoms and radiological findings, retrospectively in 69 Japanese treatment-resistant schizophrenia patients. Comparisons of the 26 weeks consecutive levels: white blood cell count with neutrophil and eosinophil, relative to their baseline levels were performed within total subjects and two groups divided by the findings of pneumonia. The crude odds ratios with 95% confidence intervals for developing pneumonia and potential confounders were calculated. The levels of eosinophils significantly increased at 1 month in each group. The introduction season between October and January and higher eosinophil level at first month were correlated with the risk of pneumonia, which occurred independent of clozapine dosage and term and relapsed in subjects when developed within initial 1 month. Clozapine-induced eosinophilic pneumonia was considered transient and reversible, however, the risks and benefits must be considered and close monitoring should be done to avoid life-threatening conditions during clozapine treatment.