Clinical relevance of cytochrome P450-mediated drug-drug interactions in hospitalised older adults: implications for community pharmacy.

Cytochrome P450 (CYP)-mediated drug-drug interactions constitute a relevant safety issue in hospitalised older patients, due to multimorbidity and polypharmacy. The objective was to characterise these interactions and analyse the factors associated with their occurrence. A retrospective observational study was conducted in a cohort of patients aged ≥ 65 years admitted between 2020 and 2023. Data from the electronic prescribing system were analysed using descriptive statistics, bivariate analysis and multivariate logistic regression, evaluating the association between clinically relevant interactions and clinical and demographic variables. CYP3A4 was the most frequently involved isoenzyme, followed by CYP2C19 and CYP2D6. Although the total number of interactions was high, only a proportion was considered clinically relevant. In the multivariate analysis, polypharmacy was independently associated with the presence of interactions, whereas age, sex, Charlson index and admission diagnosis showed no significant association. These results highlight the need for pharmacist-led medication reconciliation and coordinated deprescribing strategies between hospital and community pharmacy, emphasising the role of the latter in detecting clinically relevant interactions, especially during care transitions after hospital discharge.