Clinically Significant Potential Drug–Drug Interactions among Older Outpatients in Vietnam: Prevalence and Associated Factors in a Cross-sectional Study

A BSTRACT Objective: The objective of this study was to estimate the prevalence, severity, mechanisms, actionable high-severity pairs, and associated factors of clinically significant potential drug–drug interactions (DDIs) in older outpatients in Vietnam. Methods: We conducted a descriptive cross-sectional prescription study using systematic random sampling of 909 health-insurance outpatient prescriptions for patients aged 60 years or older at a provincial referral general hospital from April 2021 to April 2022. Potential DDIs were screened with Drugs.com and Medscape (final access: June 30, 2022). Severity ratings were harmonized into three levels; level 1 and level 2 interactions were considered clinically significant. Associated factors were evaluated using multivariable logistic regression. Findings: The mean age was 72.92 ± 8.88 years, and 236 patients (26.0%) were women. Polypharmacy (five or more medicines) occurred in 685 prescriptions (75.4%). Overall, 725 prescriptions (79.8%) contained at least one clinically significant potential DDI, including 84 (9.2%) with at least one level 1 pair. The mean number of clinically significant potential DDIs per prescription was 2.51 ± 2.41. Among 2745 DDI occurrences involving 325 unique pairs, pharmacodynamic mechanisms predominated, especially synergism (1382; 50.4%), and antagonism (527; 19.2%). Polypharmacy was the strongest associated factor (adjusted odds ratio 9.69, 95% confidence interval 6.21–15.11; P < 0.001). Conclusion: Clinically significant potential DDIs were frequent in older Vietnamese outpatients. Combining polypharmacy-based triage with a locally prioritized list of high-severity pairs may help outpatient pharmacists and prescribers convert routine database screening into focused medication-safety actions.