Population-based study of long-term mortality risk associated with clozapine use among patients with schizophrenia

Background
Patients with schizophrenia have a significantly elevated risk of mortality. Clozapine is effective for treatment-resistant schizophrenia, but its use is limited by side-effects. Understanding its association with mortality risk is crucial.

Aims
To investigate the associations of clozapine with all-cause and cause-specific mortality risk in schizophrenia patients.

Method
In this 18-year population-based cohort study, we retrieved electronic health records of schizophrenia patients from all public hospitals in Hong Kong. Clozapine users (ClozUs) comprised schizophrenia patients who initiated clozapine treatment between 2003 and 2012, with the index date set at clozapine initiation. Comparators were non-clozapine antipsychotic users (Non-ClozUs) with the same diagnosis who had never received a clozapine prescription. They were 1:2 propensity score matched with demographic characteristics and physical and psychiatric comorbidities. ClozUs were further defined according to continuation of clozapine use and co-prescription of other antipsychotics (polypharmacy). Accelerated failure time (AFT) models were used to estimate the risk of all-cause and cause-specific mortality (i.e. suicide, cardiovascular disease, infection and cancer).

Results
This study included 9,456 individuals (mean (s.d.) age at the index date: 39.13 (12.92) years; 50.73% females; median (interquartile range) follow-up time: 12.37 (9.78-15.22) years), with 2020 continuous ClozUs, 1132 discontinuous ClozUs, 4326 continuous non-ClozUs and 1978 discontinuous Non-ClozUs. Results from adjusted AFT models showed that continuous ClozUs had a lower risk of suicide mortality (acceleration factor 3.01; 99% CI: 1.41-6.44) compared with continuous Non-ClozUs. Continuous ClozUs with co-prescription of other antipsychotics exhibited lower risks of suicide mortality (acceleration factor 3.67; 1.41-9.60) and all-cause mortality (acceleration factor 1.42; 1.07-1.88) compared with continuous Non-ClozUs. No associations were found between clozapine and other cause-specific mortalities.

Conclusions
These results add to the existing evidence on the effectiveness of clozapine, particularly its anti-suicide effects, and emphasise the need for continuous clozapine use for suitable patients and the possible benefit of clozapine polypharmacy.