Targeted cancer therapy: interactions with other medicines

Targeted therapy drugs, mainly those within the signal transduction inhibitors, are used more chronically than cytotoxic drugs and are metabolised by cytochrome P450 isozymes so patients are at high risk of having drug-drug interactions (DDI). Not only this, as the majority of them are given orally, new drug-drug interactions concerning gastrointestinal absorption can occur (e.g., with proton pump inhibitors). DDI can lead to changed systemic exposure, resulting in variations in drug response of the co-administered. In addition, concomitant ingestion of dietary supplements could also alter systemic exposure of drugs, thus leading to adverse drug reactions or loss of efficacy. In this review, we give an overview of the current existing data of known or suspected DDI between targeted therapy and other medicines. A review of package inserts was performed to identify drug-drug interactions for all targeted antineoplastic agents. Tertiary databases such as Lexicomp^®, Drugs, Martindale, Facts and Comparisons^®, and AHFS Drug Information were also referenced. This study covered 40 targeted antineoplastic agents (28 signal transduction inhibitors, 9 monoclonal antibodies and 3 other drugs, 2 monoclonal antibody conjugates and 1 fusion protein). Most of targeted therapy drugs are major CYP3A4 substrates with P-gp playing an important role in disposition too. Thus, there is a very common thread here that these agents will likely be sensitive victims to strong CYP3A4/P-gp inhibitors and inducers. It is essential that health care providers monitor patients for potential DDI to avoid a loss in efficacy or risk of greater toxicity from targeted therapy.