Prevalence of the concurrent administration of contraindicated medications in patients with cancer treated with tyrosine kinase inhibitors (TKIs): A pilot study from the IU Simon Comprehensive Cancer Center.
e18714 Background: Polypharmacy may result in drug-drug interactions that reduce efficacy or increase toxicities to patients. Tyrosine kinase inhibitors (TKIs), which is standard therapy for many patients with cancer, have interactions with many commonly prescribed drugs (including proton pump inhibitors [PPIs] and cytochrome inhibitors/inducers) which alter their metabolism. Methods: Retrospective study of 100 consecutively chosen patients with advanced cancer treated with TKIs were identified. Patients < 18 years of age, participating in clinical trials, or taking an investigational treatment for their cancer were excluded. TKI start date and concurrent medications were identified from chart reviews. Documentation was undertaken to record co-administration of drugs that could prolong QT interval, PPIs, and CYP3A inhibitors and inducers. QT prolonging medications were divided into those with known risk (KR), conditional risk (CR), and probable risk (PR). IUSM Clinical Pharmacology Flockhart table was utilized for cytochrome drug interactions. All three categories of cytochrome inhibitors (strong, moderate, and weak) were included in the analysis. The primary objective was to estimate the percentage of patients treated with TKIs co-administered these classes of drugs with a potential for harmful drug-drug interaction. Results: Median age of 100 pts was 57 and median duration of treatment with the TKI was 441 days. 85 of 100 pts receiving TKIs for their cancer were also prescribed at least 1 drug with the potential for drug-drug interaction, including 39 with a QT prolonging drug with known risk and 25 with a CYP3A inducer or inhibitor. 53% had documentation of EKG while on TKI treatment. Conclusions: Most patients in this chart review were co-administered TKIs with other agents with a potential for harmful drug-drug interactions. Continual monitoring of medications is necessary to optimize efficacy of TKIs and reduce the chance for harmful side effects.[Table: see text]