Potential Drug Interactions in Cancer Patients Receiving Supportive Care Exclusively

Riechelmann, Rachel P.; Zimmermann, Camilla; Chin, Sheray N.; Wang, Lisa; O'Carroll, Aoife; Zarinehbaf, Sanaz; Krzyzanowska, Monika K.

doi:10.1016/j.jpainsymman.2007.06.009

« Previous Next »Journal of Pain and Symptom Management
Volume 35, Issue 5 , Pages 535-543, May 2008

Potential Drug Interactions in Cancer Patients Receiving Supportive Care Exclusively

Rachel P. Riechelmann, MD
- Department of Medical Oncology and Hematology, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada
Camilla Zimmermann, MD, MPH
- Department of Psychosocial Oncology and Palliative Care, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada
Sheray N. Chin, MD
- Department of Medical Oncology and Hematology, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada
Lisa Wang, BSc
- Department of Biostatistics, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada
Aoife O'Carroll, MD
- Department of Medical Oncology and Hematology, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada
Sanaz Zarinehbaf, MD
- Department of Psychosocial Oncology and Palliative Care, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada
Monika K. Krzyzanowska, MD, MPH
- Department of Medical Oncology and Hematology, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada
- Address correspondence to: Monika K. Krzyzanowska, MD, MPH, Department of Medical Oncology and Hematology, Princess Margaret Hospital, 610 University Avenue, Suite 5-227, Toronto, ON M5G 2M9, Canada.

Accepted 21 June 2007. published online 13 February 2008.

Abstract

Cancer patients at the end of life often take many medications and are at risk for drug interactions. The purpose of this study was to describe the epidemiology of potential drug interactions in cancer patients receiving supportive care exclusively. We retrospectively reviewed the charts of consecutive adult cancer outpatients attending palliative care clinics at the Princess Margaret Hospital, Toronto, Canada. Drugs were screened for interactions by the Drug Interaction Facts software, which classifies interactions by levels of severity (major, moderate, and minor) and scientific evidence (1–5, with 1=the strongest level of evidence). Among 372 eligible patients, 250 potential drug interactions were identified in 115 patients (31%, 95% confidence interval 26%–36%). The most common involved warfarin and phenytoin. Most interactions were classified as being of moderate severity (59%) and 42% of them were supported by Levels 1–3 of evidence. In multivariable analysis, increasing age (P<0.001), presence of comorbidity (P=0.001), cancer type (brain tumors, P<0.001), and increasing number of drugs (P<0.001) were associated with risk of drug interactions. Potential drug interactions are common in palliative care and mostly involve warfarin and anticonvulsants. Older patients, those with comorbid conditions, brain tumor patients, and those taking many medications are at greater risk of drug interactions.