Ordinary Medicines Interfering With Cancer Drugs

Cancer drug potency and toxicity can be impacted by other meds

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Over the past decade, oral cancer medications have revolutionized treatment, sometimes turning once terminal diseases into chronic conditions. How these drugs interact with other medicines is just now coming to light, and vigilance is the watchword.

A new study finds that ordinary medications such as antibiotics can interfere with the effectiveness of a class of oral cancer drugs, known as kinase inhibitors.

These drug interactions can lessen the potency of the cancer medications that target enzymes in tumor cells, or may increase the risk of toxic side effects.

"Tell your doctor about all medications you're taking - all of them."

A Medco Research Institute uncovered that 23-74 percent of patients taking one of nine oral cancer drugs were also taking medicines that could produce a potentially negative interaction with the drug therapy. 

"Oral cancer drugs represent a huge advancement in oncology treatment, but make no mistake these are powerful drugs," said Dr. Milayna Subar, national practice leader at the Medco Oncology Therapeutic Resource Center. 

He added, "These high cost medications can have severe side effects and need to be actively monitored for proper use and adherence." 

The nine cancer drugs that are vulnerable to negative interactions include the following:

The drugs that could cause drug-drug interactions include:

  • Antibiotics (certain types)
  • Antifungal agents
  • Calcium channel blockers used for blood pressure and heart conditions
  • Proton pump inhibitors (PPIs) used for gastrointestinal problems including ulcers
  • Steroids

For the study, the pharmacy claims of some 11,600 patients taking one of the nine kinase inhibitors were evaluated and examined to see the number of patients taking at least one other drug that could interfere with the effectiveness of their cancer treatment.

Kinase inhibitors treat different types of cancer, including leukemia, breast, lung, kidney, pancreatic, and gastrointestinal cancers, among others. A year's supply of these medications can cost more than $100,000.

"Oncologists are not always aware of other medications prescribed by other doctors and vice-versa, which can pose a real hazard for their patients on oral cancer therapies," said Dr. Steve Bowlin, senior director and therapeutic area research lead, MRI, and a co-author of the study.

The Medco team found several dangerous trends:

  • Of the patients taking Gleevec, 43 percent were prescribed a drug that could lower the efficacy of the cancer therapy, and 68 percent took a drug that could raise toxicity of the treatment.
  • The efficacy of the other cancer drugs was potentially impaired 23-57 percent of the time.
  • Somewhere between 24-74 percent of patients were taking medications that were capable of making the cancer drugs more toxic.

"By taking a holistic approach to caring for cancer patients and being diligent that they are managing their treatment regimen properly and getting the full benefit of the medications they are on, we can drive down both waste and cost, while helping to improve the health outcomes of the patient," said Subar. 

These findings were presented at the 2012 American Society for Clinical Pharmacology and Therapeutics(ASCPT) Annual Meeting.

It should be noted that until published in a peer-reviewed journal, findings are considered preliminary.

A pharmacy benefit management company, Medco offers a program in which oncology pharmacists let physicians know about potentially negative drug-drug interactions.

Reviewed by: 
Review Date: 
March 18, 2012
Last Updated:
March 19, 2012