The letter explains that hydroxychloroquine, proposed for COVID‑19 treatment in older adults, has a narrow therapeutic window, slow elimination, and variable pharmacokinetics, which makes drug–drug interactions (DDIs) particularly relevant in this population. The authors describe an analysis of chronic medication in 377 older adults from Northern Spain, in which they identify 47 drugs and highlight 12 frequently used agents (amiodarone, rifampicin, phenobarbital, phenytoin, carbamazepine, digoxin, citalopram, dabigatran, hydroxyzine, nortriptyline, salmeterol and apixaban) as having clinically important potential interactions with hydroxychloroquine that may contraindicate coadministration or demand close monitoring. These interactions are mainly related to effects on CYP2D6 metabolism, P‑glycoprotein transport, and additive QT‑interval prolongation, leading the authors to recommend that clinicians carefully review polypharmacy and monitor for DDIs when prescribing hydroxychloroquine to elderly COVID‑19 patients
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