Prevalence of cytochrome P450‐mediated potential drug–drug interactions in residents of intermediate care facilities for older adults in Japan

Aim Limited information is available on the prevalence of drug–drug interactions (DDI) in residents of long‐term care facilities who often receive multiple drugs. This study aimed to evaluate the prevalence of clinically relevant cytochrome P450‐mediated potential DDI in residents of intermediate care facilities for older adults (called Roken) in Japan. Methods A nationwide drug utilization study was carried out for Roken residents in 2015 (up to five residents per facility). Potential DDI were identified with an explicit list of drugs that can be involved in clinically relevant cytochrome P450‐mediated DDI in Japan. Logistic regression was used to evaluate the association of the number of drugs prescribed with the presence of potential DDI, adjusted for age, sex and long‐term care needs level. Results The study included 1222 residents of 348 Roken who were prescribed two or more active drug substances. The participants who received ≥6 and ≥10 drugs represented 49% and 10% of total participants, respectively. In total, 42 two‐drug combinations involving potential DDI were identified in 33 participants (2.7%) – benzodiazepines, proton pump inhibitors, calcium channel blockers and anti‐epileptic drugs were frequently involved. The adjusted odds ratios for potential DDI were 2.84 (95% confidence interval 1.15–7.02) or 7.82 (95% confidence interval 2.96–20.70) in residents receiving six to nine drugs or ≥10 drugs, compared with those receiving two to five drugs. Conclusions Approximately 3% of Roken residents were at risk for clinically relevant DDI. Reducing the number of drugs prescribed through medication reviews would mitigate the potential risk. Geriatr Gerontol Int 2019; 19: 513–517.