The most important element in the treatment of schizophrenia or SSP is pharmacotherapy, and in most cases these disorders require lifelong drug therapy [11]. However, despite the high prevalence of these disorders, it is not easy to determine the extent to which patients maintain drug adherence. Therefore, as an alternative, this study analyzed the MPR of the patients of schizophrenia or SSP as an important index in the treatment of schizophrenia and SSP. In the case of Korea, since, citizens are covered by national health insurance, it was possible to analyze representative data. Several previous studies have analyzed schizophrenia's MPR in different countries. One study was conducted only for Florida Medicaid recipients, and the other study was for the patients who were diagnosed as schizophrenia for the first time in Korea [7−22]. The present study was based on national data for five years to ensure representativeness, and is meaningful in that it is the first study to analyze drug adherence following previous studies of incidence and prevalence studies of schizophrenia and SSP patients [1].
This study is similar to the abovementioned Korean study, but it is very different from the study analyzing the results of Florida in the United States [22]. In this study, the overall MPR was 79%, and although there was a difference depending on the type of drug, the groups showing 80% to 100% of MPR were observed in 62% to 72% of the total patient group, and in those showing less than 50% MPR, the patient group was observed to be 8% to 15% depending on the type of drug, which showed a huge difference from the results of Korea. In addition, this result was due to great resistance to medication. In Korea, traditionally, mental illness has been surrounded by stigma [23, 24]. The fact that the duration of untreated psychosis in Korea is very long compared to other countries also bears out this fact [25, 26].
As a result of the analysis of this study, the average value of MPR was only 45.8%, and 50.8% of patients receiving medication for schizophrenia and SSP were in the MPR group of less than 40%. Since, this study did not include patients who were not admitted to the hospital, were not prescribed antipsychotics, it can be concluded that the drug adherence of schizophrenia and SSP patients in Korea is very low.
In this study, in the comparative analysis of each MPR group by section, it was found that the higher the MPR group, the higher the proportion of medical aid patients. In addition, the percentage of hospitalization experiences at general hospitals or mental health clinics was reduced, and the average number of days of hospitalization by group was not significantly different around 20 days. This is in line with the analysis of the risk factor of low MPR. Compared to a case where outpatient treatment in a psychiatric hospital occupies the most part of treatment, the experience of hospitalization in a general hospital or a psychiatric hospital was highly correlated with the risk of low MPR (<40%).
The major issue observed in this study was that the proportion of patients over 65 years of age was very high. Due to the medical characteristics of the Republic of Korea, diagnostic leniency required to use medications was considered to be attributed to off-label in Korea. Although there was a difference in the figures, the risk factor of low MPR was the same as that of general hospital, mental hospital admission, and outpatient treatment of general hospital. Compared to the capital city, Seoul, similarities were also associated with risk when receiving treatment in six metropolitan and other cities. However, the only difference was that the risk association between health insurance and medical aid patients was not statistically significant.
This study has some limitations. First, since, the study was based on medical insurance claim data, it was difficult to evaluate the contents of clinical conditions of each individual such as the reason of restarting medication or changing the regimen. Second, in this study, drug adherence was estimated with the MPR value, but in fact, possessing a drug may not necessarily mean consuming the drug; hence, this is a conceptual limitation of the study. The overall adherence was critically low even though we used MPR for adherence calculation and added up all the prescribed days. MPR is the sum of the days' supply for all fills of a given drug in a particular time period, divided by the number of days in the time period. Therefore, if an individual refills the medication before the former prescription ends, it can lead to overestimation of adherence. Third, in view of the concept that the drug should be consumed for a lifetime, it may be difficult to conclude that examining only the specific time period determined for this study (2011−2015) accurately reflects the exact drug adherence of a patient. However, this study is meaningful in that it is a study of citizens in one country, and in that it is the first study to investigate drug adherence of schizophrenia and SSP, which require lifelong drug treatment. Even though we did not apply a stricter method of calculation such as PDC, adherence to antipsychotic drugs of SSP patients was found to be low.