High-Cost Users of Prescription Drugs: National Health Insurance Data from South Korea.

Importance: In OECD countries, pharmaceutical spending reached around 800 billion USD in 2013, accounting for about 20% of total spending in the retail sector. Pharmaceutical expenditures are steadily increasing in South Korea, necessitating strategies to promote efficiency.

Objective: This study investigated factors associated with high-cost users (HCUs), who account for the majority of outpatient prescriptions in the total South Korean population. The top 20 frequently prescribed therapeutic subgroups were also investigated.

Design: This is an observational study performed using health insurance claims data in 2019.

Participants: In total, 44,744,632 people (including 6,806,339 aged 65 years or older) who were prescribed outpatient medications were included.

Main Measures: HCUs were defined as those for whom prescription drug costs were in the top 5%. Multivariate logistic regression analysis was performed using factors including age, insurance type, number of prescription drugs, outpatient visit days, prescription treatment days, and chronic diseases.

Results: HCUs accounted for 3.6 million (5% of the total population) and 1.4 million (21.1% of those 65 years or older). Furthermore, 4.1% of HCUs in the total population had few comorbidities. Male sex, older age, insurance (Medical Aid), comorbidities, chronic diseases, number of prescription drugs, outpatient visit days, and prescription days were all associated with an increased probability of being an HCU. The highest spending was found for B01 (antithrombotic agents) with 0.4 billion USD, followed by C10 (lipid-modifying agents) and A10 (drugs used in diabetes). The proportion of spending for HCUs among the general population was highest in L01 (antineoplastic agents), at 98.2%, and L04 (immunosuppressants), at 87.8%, whereas among the elderly, the highest proportions were found for B01 (antithrombotic agents), at 44.5%, and N06 (antidepressants), at 44.3%.

Conclusion: Age and multiple chronic conditions were strongly associated with HCUs, and it seems necessary to reduce drug prescriptions in patients without complex comorbidities. Several measures should target those without multiple chronic conditions who are nonetheless HCUs.