Adherence to antipsychotic drugs by medication possession ratio for schizophrenia and similar psychotic disorders in the Republic of Korea: A retrospective cohort study
Sung Joon Cho 1, 2, Jungmee Kim 3, Jin Yong Lee 4, 5, Jee Hoon Sohn 6, 7*
1Department of Psychiatry, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea, 2Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea, 3Workplace Mental Health Institute, Kangbuk Samsung Hospital, Seoul, 4Department of Public Health and Community Medicine, Seoul Metropolitan Government, Seoul National University Boramae Medical Center, Seoul, Republic of Korea, 5Department of Health Policy and Management, Seoul National University College of Medicine, Seoul, Republic of Korea, 6Institute of Public Health and Medical Service, Seoul National University Hospital, Seoul, Republic of Korea, 7Department of Psychiatry, Seoul National University Hospital, Seoul, Republic of Korea
Received: March 2, 2021; Revised: April 12, 2021; Accepted: April 12, 2021; Published online: April 12, 2021.
© The Korean College of Neuropsychopharmacology. All rights reserved.

Abstract
Objective: Pharmacotherapy is considered as an essential element in the treatment of schizophrenia and schizophrenia similar psychosis (SSP). Discontinuation of antipsychotic drugs increases medical use and economic burden. Therefore, maintenance of drug treatment is essential to reduce the social burden caused by schizophrenia and SSP and it is important to investigate the maintenance rate. 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 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 among these patients 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 “psychiatric hospital outpatient,” the experience of “psychiatric hospital admission,” the experience of “general hospital admission,” and patients receiving “medical aid” showed less risk of having statistically significant low MPR (< 40%).
Conclusions: 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.
Keywords: Psychotic disorders, Schizophrenia, Medication adherence, Pharmacotherapy, Medication possession ratio


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