Cancer patients are at high risk for potential drug interactions

Potential drug interactions from prescribed medications are common among cancer patients and may cause unnecessary harm, according to a study in the April 18 Journal of the National Cancer Institute.

Cancer patients often take several medications at the same time, not only for treating their cancer but also for side effects and other secondary illnesses. Because of this, they can be at high risk for adverse drug interactions and duplicate medications. Consequences of these interactions can range from inactivation of cancer-fighting medications to severely injuring or killing the patient.

Rachel Riechelmann, M.D., of the Princess Margaret Hospital in Toronto, and colleagues gave 405 cancer patients a questionnaire about the medications they had taken in the last four weeks. Their responses were analyzed using a drug interaction software program that could identify potential interactions and rank them by severity.

Nearly a third of patients were exposed to at least one potential drug interaction. The researchers identified 276 drug combinations with the potential to interact. About nine percent of the interactions considered of major severity, risk of death, and 77 percent of moderate severity, risk of serious health problems. About eight percent of the patients received duplicate medications.

The researchers found that some of the drugs interacted with anticancer medications. The most common were warfarin (a drug to prevent blood clots), antihypertension drugs, aspirin and anticonvulsants. Warfarin stood out because it can cause hemorrhages when used with certain chemotherapy medications, and the interaction can interfere with its metabolism. Additionally, patients with brain tumors were at particularly high risk since they are often prescribed anticonvulsants.

"We suggest that patients at high risk, be routinely screened for potential drug interactions. The development of medication databases and computerized physician medication order entry linked to screening electronic programs could help health professionals to identify dangerous drug combinations and monitor prescriptions of agents with high risks of interactions," the authors write.

In an accompanying editorial, Peter Norton, M.D., of the University of Calgary, and G. Ross Baker, Ph.D., of the University of Toronto, agree that a better system for tracking patients' medications is needed. "We believe that such coordination and communication have the potential to substantially reduce the incidence of and mitigate possible harm from the potential drug interactions that have been discovered by Riechelmann [and colleagues]. In other high-risk industries, such as aviation and the offshore oil industry, many errors result from poor coordination and communication, and in these areas, strategies to improve team coordination and communication have led to reductions in incidents," the authors write.