# Impact of the 2018 Japan Floods on Methotrexate and Antirheumatic Drug Prescriptions: A Longitudinal Analysis of the Japanese National Database

## TL;DR

The 2018 Japan Flood led to increased new prescriptions of methotrexate among disaster victims compared to non-victims.

## Contribution

This study is the first to show that a large-scale disaster increased new methotrexate prescriptions for rheumatic diseases.

## Key findings

- New methotrexate prescriptions were significantly higher in disaster victims than non-victims.
- No significant association was found between victim status and methotrexate prescriptions before the disaster.
- A non-significant increase in other antirheumatic drug prescriptions was observed among victims.

## Abstract

Most rheumatic diseases are caused by a complex interplay of genetic, physical, and environmental factors. Large-scale disasters affect all of these factors; however, their impact on rheumatic diseases is unknown. We aimed to investigate changes in antirheumatic drug prescriptions among victims and non-victims after the 2018 Japan Flood: the second largest water-related disaster in Japan.

In this retrospective cohort study, we used data from the Japanese National Database of Health Insurance Claims, which included information on all drugs prescribed by physicians. We included all cases of prescription at medical institutions in disaster-stricken areas between July 2017 and June 2019. The newly initiated prescription of methotrexate (MTX, 2-mg tablets or capsules), which has been exclusively approved for rheumatoid arthritis, juvenile idiopathic arthritis, or psoriatic arthritis/psoriasis in Japan, and other antirheumatic drugs within the first year after the disaster were evaluated for government-certified disaster victims and non-victims. Baseline characteristics and MTX prescription status in the pre-disaster period were also assessed to compare the groups.

In the pre-disaster period, no significant association was found between victim status and MTX prescription. The number of individuals who had not been prescribed MTX before the disaster was 4,973,401, including 31,006 victims. Among them, 14,908 (including 110 victims) had a history of MTX prescription after the disaster. In the MTX-naive group, new MTX prescriptions within one year after the disaster were significantly more frequent in victims than in non-victims (age- and sex-adjusted hazard ratio: 1.83; 95% confidence interval: 1.37-2.46). Similarly, a non-significant increase in prescriptions for conventional synthetic/biological disease-modifying antirheumatic drugs was observed.

Victims of the 2018 Japan Flood were more likely to be prescribed MTX for the first time.