© The Author 2007. Published by Oxford University Press.
ARTICLES |
Potential Drug Interactions and Duplicate Prescriptions Among Cancer Patients
Affiliations of authors: Departments of Medical Oncology and Hematology (RPR, IFT, MKK) and Biostatistics (LW), Princess Margaret Hospital, Toronto, ON, Canada; Dendrix, Ltd, Sao Paulo, Brazil (EDS); Department of Public Health Sciences, University of Toronto, Toronto, ON, Canada (NAT)
Correspondence to: Monika K. Krzyzanowska, MD, MPH, Department of Medical Oncology and Hematology, Princess Margaret Hospital, 610 University Ave, Ste 5-227, Toronto, ON, M5G 2M9, Canada (e-mail: monika.krzyzanowska{at}uhn.on.ca).
Background: Cancer patients receive numerous medications, including antineoplastic agents, drugs for supportive care, and medications for comorbid illnesses. Therefore, they are at risk for drug interactions and duplicate prescribing.
Methods: A questionnaire eliciting information on demographics and medications taken in the previous 4 weeks was given to adult outpatients receiving systemic anticancer therapy for solid tumors. The Drug Interaction Facts software, version 4.0, was used to identify potential drug interactions and to classify them by level of severity (major, moderate, or minor) and the strength of scientific evidence for them (using categories [1–5] of decreasing certainty). Summary statistics and logistic regression were used to analyze the data. All statistical tests were two-sided.
Results: The survey was completed by 405 patients. We observed 276 potential drug interactions, and at least one potential interaction was identified in 109 patients (27%; 95% confidence interval [CI] = 23% to 31%). Of the potential interactions, 25 (9%) were classified as major and 211 (77%) as moderate. Nearly half (49%) of potential interactions were supported by level 1 or 2 scientific evidence. Most potential drug interactions (87%) involved non-anticancer agents such as warfarin, antihypertensive drugs, corticosteroids, and anticonvulsants, but some (n = 36, 13%) involved antineoplastic agents. In multivariable analysis, increased risk of receiving drug combinations in which there were potential drug interactions was associated with receipt of increasing numbers of drugs (odds ratio [OR] = 1.4 per additional drug, 95% CI = 1.26 to 1.58, P<.001 from the Wald chi-square test), type of medication (drugs to treat comorbid conditions versus supportive care medications only; OR = 8.6, 95% CI = 2.9 to 25, P<.001), and the presence of brain tumors. Thirty-two (8%) patients were exposed to duplicate medications, most often corticosteroids, proton pump inhibitors, or benzodiazepines.
Conclusion: Potential drug interactions were common among cancer patients and most often involved medications to treat comorbid conditions. Duplicate medications were infrequent.
| CONTEXT AND CAVEATS Prior knowledge Cancer patients are often prescribed many medications concurrently; in addition to chemotherapeutic agents, they may receive drugs to treat non-neoplastic conditions as well as medicines for supportive care. The extent to which they are exposed to adverse drug interactions is unknown. Study design Information on individual exposure to various medications in a random sample of an outpatient population was collected by questionnaire, and potential drug interactions were identified using a software program that accessed published data on drug interactions. Contribution Potential interactions were identified in 27% of patients and classified according to severity, level of scientific evidence supporting the interaction, type of medications involved, type of cancer, and other parameters. Most of the potential interactions involved medications to treat comorbid conditions. Implications The results suggest the importance of further studies to determine the frequency of adverse drug interactions in cancer patients. Limitations The study was not designed to determine how often the potential drug interactions identified actually resulted in adverse clinical consequences for patients.
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Manuscript received July 12, 2006; revised February 7, 2007; accepted March 19, 2007.
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Editorial about this Article
- Patient Safety in Cancer Care: A Time for Action
- Peter G. Norton and G. Ross Baker
J Natl Cancer Inst 2007 99: 579-580.[Extract] [Full Text] [PDF]
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