Clozapine use tied to increased infection risk in schizophrenia

Among patients receiving treatment for schizophrenia, infections appear to occur at a higher rate with clozapine vs olanzapine, as shown in a study from Hong Kong.

The study included 11,051 patients (54.6 percent female) who used antipsychotics continuously for at least 90 days. Of these, 1,450 were in the clozapine group (mean age 40.59 years) and 9,601 in the olanzapine group (mean age 45.33 years). Olanzapine was selected as a comparator due to its similar chemical structure and often overlapping indication with clozapine.

The primary outcome was the occurrence of any infectious disease, with subtypes analysed as secondary outcomes. Researchers conducted propensity score-based inverse probability of treatment weighting and Cox proportional hazards regression analyses.

The incidence of infection overall was higher among clozapine users than olanzapine users (weighted incidence rate, 7.26 vs 6.00 per 100 person-years; weighted hazard ratio [HR], 1.25, 95 percent confidence interval [CI], 1.13–1.39), for a weighted absolute difference in incidence rate of 1.27 infections per 100 person-years.

Notably, the risk of infections was higher in older age groups, with weighted HRs increasing from 1.24 in those aged 18–44 years to 1.41 in those aged 45–54 years and 1.45 in those aged 55 years or older.

The increased risk of infections observed with clozapine vs olanzapine use was driven by upper and lower respiratory tract infections.

The findings underscore the need to balance the therapeutic benefits of clozapine with infection control measures, including regular monitoring and preventive strategies.