Clinical relevance of potential self-medication drug interactions in antineoplastic and immune-modulating therapy among online pharmacy customers

BACKGROUND: Modern oral antineoplastic and immune-modulating drugs offer an array of therapeutic advantages, and yet pose challenges in daily use for patients, physicians and pharmacists. In contrast to intravenous administration, these drugs are not subject to direct medical control. Recently, we have seen a huge rise in sales of non-prescription over-the-counter (OTC) medicines via the internet without any advice from a healthcare professional. OBJECTIVES: The aim of this study was to investigate whether the risk of known potential drug-drug interactions between modern oral antineoplastic and immune-modulating drugs and OTC drugs differs between sales in traditional community pharmacies versus online pharmacies. DESIGN: Real-life sales data from community and online pharmacies were used as basis for the analysis. METHODS: We determined the most frequently purchased antineoplastic and immune-modulating drug-substances in 14 local community pharmacies within the Munich area, Germany and identified the OTC substance groups that could potentially cause interactions with oncological therapies. Using sales data from 11 local community pharmacies and three online pharmacies, we investigated whether OTC purchases differed between the two sales channels. RESULTS: We identified 10 relevant OTC substance classes and detected significant variations in patients’ preferred sales channels between the drug classes. Certain OTC drugs, which seem to be bought more often over the internet, pose risks during antineoplastic and immune-modulating therapy. CONCLUSION: Patients should therefore be proactively made aware of the corresponding risks in order not to jeopardize the activity of the antineoplastic and immune-modulating drugs and thus the success of their therapy.