Potential Drug-Drug and Herb-Drug Interactions in Patients With Cancer: A Prospective Study of Medication Surveillance

Purpose: Patients with cancer frequently use herbal supplements and concomitant medications along with antineoplastic agents. These patients are at high risk of herb-drug interactions (HDIs) and drug-drug interactions (DDIs). We aimed to determine clinically relevant DDIs and HDIs leading to pharmaceutical intervention. Methods: Patients starting a new anticancer therapy were asked to complete a questionnaire to identify concomitant use of any over-the-counter drug or herbal supplement. Potential DDIs and HDIs were identified using two different databases. If a potentially clinically relevant DDI was recognized by the clinical pharmacist, a notification was sent to the prescribing oncologist, who decided whether to carry out a suggested intervention. Regression analyses were performed to identify variables associated with clinically relevant DDIs. Results: A total of 149 patients were included in this study, with 36 potentially clinically relevant DDIs identified in 26 patients (17.4%; 95% CI, 11.3% to 23.5%), all of them leading to therapy modifications. In total, four patients (2.7%; 95% CI, 0.1% to 5.3%) had experienced clinical consequences from DDIs at the time of pharmacist notification. Additionally, 84 patients (56.4%; 95% CI, 48.4% to 64.4%) reported using concurrent herbal supplements, and 122 possible HDIs were detected. Concomitant use of two or more drugs was independently associated with high risk of a clinically significant DDI (odds ratio, 2.53; 95% CI, 1.08 to 5.91; P = .03). Conclusion: Potentially clinically relevant DDIs and possible HDIs were frequently detected in this prospective study. A multidisciplinary approach is required to identify and avoid potentially harmful combinations with anticancer therapy.