Adherence to Antipsychotic Drugs by Medication Possession Ratio for Schizophrenia and Similar Psychotic Disorders in the Republic of Korea: A Retrospective Cohort Study

Objective: Pharmacotherapy is considered as an essential element in the treatment of psychotic disorders including schizophrenia. Discontinuation of antipsychotic drugs increases medical use and economic burden. Therefore, main-tenance of medication is essential to reduce the social burden caused by schizophrenia and schizophrenia similar psy-chosis (SSP), and hence, it is important to investigate the rate at which pharmacotherapy is maintained. Therefore, this study aimed to examine the current status of drug compliance using national health insurance data. Methods: This was a retrospective cohort study, which analyzed data from the nationwide insurance claims database. A total of 343,134 patients who were newly diagnosed with schizophrenia and SSP during 2011-2015. The adherence to antipsychotic drugs was assessed by medication possession ratio (MPR) and the risk factors of poor adherence were defined as MPR < 40%. Results: The average of the MPRs was 45.8%, and the proportion of patients with less than 40% of MPR was 50.8%. It was found that female patients, the experience of "general hospital outpatient," "psychiatric hospital admission," "general hospital admission," and patients receiving "health insurance" showed high risk of having statistically significant low MPR (< 40%). Conclusion: In this study, the drug adherence of schizophrenia and SSP patients currently under treatment, as estimated by MPR, was very low. However, it was also found that the MPR was high among patients receiving medical aid, with less medical expenses. Thus, it is possible to consider an institutional mechanism in which schizophrenia and SSP patients can be treated with less economic burden.