Taking a pill to fight cancer? Avoid these dangerous drug interactions

Common cancer treatments nowadays include not just radiation, surgery, and infusion chemotherapy treatments, but also pills that patients take every day for weeks, months, or even years. Many of these pills, however, interact with common medications such as acid blockers and antihistamines, rendering the cancer drugs less effective or dangerously potent.

The majority of cancer patients prescribed a particular kind of oral cancer drug, known as kinase inhibitors, were taking other medications that interacted negatively with these drugs, according to a new survey released Friday by the nonprofit Medco Research Institute.

Reviewing pharmacy claims of about 11,600 patients on kinase inhibitors - including imatinib (Gleevec) and erlotinib (Tarceva) - the study researchers found that many patients were also taking proton pump inhibitors, steroids, calcium channel blockers, and certain antibiotics and antifungal agents that either made their cancer-fighting drugs more potent or lessened their effectiveness. Most of the time, patients were using these drugs over-the-counter or having them prescribed by their primary care physician without the knowledge of their oncologist.

“Since these are drugs launched in the past decade for fairly small patient populations, we are learning more about how they are used in real-world settings as compared to traditional clinical trials that test safety and efficacy in a tightly-controlled environment,” study co-author Dr. Steve Bowlin said in a statement. “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.”

The study found that 43 percent of the 4,617 patients receiving imatinib, often used to treat leukemia and other blood cancers, were prescribed a drug that may diminish the cancer drug’s efficacy and 68 percent of patients received a drug that may raise the level of toxicity of the treatment.

What is Gleevec? Gleevec (imatinib) interferes with the growth of some cancer cells.

Gleevec is used to treat a certain types of leukemia (blood cancer) such as Philadelphia chromosome positive chronic myeloid leukemia (CML). It is also used to treat certain tumors of the stomach and digestive system.

What is Tarceva?

Tarceva (erlotinib) is a cancer medication that interferes with the growth of cancer cells and slows their spread in the body.

Tarceva is used to treat non-small cell lung cancer. Tarceva is also used in combination with other cancer medicine to treat pancreatic cancer.

While the study looked only at kinase inhibitors, those taking other oral cancer drugs also have to be careful about drug-drug interactions. Breast cancer patients taking tamoxifen, for example, should not take the arthritis medication since it can reduce tamoxifen’s effectiveness. They also shouldn’t take the antidepressants and for the same reason.