Interactions in cancer treatment considering cancer therapy, concomitant medications, food, herbal medicine and other supplements.

Purpose: The aim of our study was to analyse the frequency and severity of different types of potential interactions in oncological outpatients' therapy. Therefore, medications, food and substances in terms of complementary and alternative medicine (CAM) like dietary supplements, herbs and other processed ingredients were considered.

Methods: We obtained data from questionnaires and from analysing the patient records of 115 cancer outpatients treated at a German university hospital. Drug-drug interactions were identified using a drug interaction checking software. Potential CAM-drug interactions and food-drug interactions were identified based on literature research.

Results: 92.2% of all patients were at risk of one or more interaction of any kind and 61.7% of at least one major drug-drug interaction. On average, physicians prescribed 10.4 drugs to each patient and 6.9 interactions were found, 2.5 of which were classified as major. The most prevalent types of drug-drug interactions were a combination of QT prolonging drugs (32.3%) and drugs with a potential for myelotoxicity (13.4%) or hepatotoxicity (10.1%). In 37.2% of all patients using CAM supplements the likelihood of interactions with medications was rated as likely. Food-drug interactions were likely in 28.7% of all patients.

Conclusion: The high amount of interactions could not be found in literature so far. We recommend running interaction checks when prescribing any new drug and capturing CAM supplements in medication lists too. If not advised explicitly in another way drugs should be taken separately from meals and by using nonmineralized water to minimize the risk for food-drug interactions.