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Herbal remedy cuts effectiveness of anticancer pill
BUFFALO Nov. 8, 2004 The herbal antidepressant St. John's Wort undercuts the effectiveness of the leukemia pill,' according to a new study.
The study, is the first to show that St. John's Wort may compromise the effectiveness of Gleevec® (imatinib mesylate, Novartis, Inc.), the revolutionary anticancer drug that has significantly improved the treatment of chronic myeloid leukemia (CML). Led by Dr. Patrick F. Smith, assistant professor in the School of Pharmacy and Pharmaceutical Sciences at the University at Buffalo, the researchers report their findings in the November issue of the journal Pharmacotherapy.
"We found that St. John's Wort may significantly reduce the effect of Gleevec® by lowering blood levels to the point where patients may fail therapy if they take both together," Smith said in a news release.
Recent surveys show that as many as one-third to one-half of all cancer patients report using alternative medications, while other studies have shown that such medications as St. John's Wort and certain vitamin supplements may interfere with chemotherapy.
"Patients may not view alternative products as 'medications,' and thus they frequently go unreported to the patient's physician or pharmacist," Smith said. "For the most part, patients often times don't necessarily need these herbal products, and don't know that there may be serious drug interactions."
Gleevec®, or imatinib mesylate, was the first FDA approved drug to result from the "rationale drug development" that grew from the Human Genome Project. The drug was designed to target specific molecular features of leukemia cells caused by a genetic abnormality that results in a chromosomal rearrangement. The result is that the drug triggers cell death in leukemia cells with little harm to normal cells, unlike traditional chemotherapy drugs. While most chemotherapy is administered intravenously every few weeks for several dosing cycles, Gleevec® is taken in a daily, oral dose over the course of years.
"Hence, it is the first drug that turns cancer into a chronic disease that is treated with a tablet, similar to high blood pressure or diabetes," Smith said.
As a result, Gleevec received an expedited approval in the United States for the treatment of chronic myeloid leukemia (CML) and rapidly has become a cornerstone of cancer treatment, according to Smith.
People commonly take St. John's Wort for depression, which can be a common side effect of cancer therapy. Smith's group showed, however, that St. John's Wort increases a patient's metabolism of the medication, resulting in the body eliminating the drug more quickly than normal. This lowers the blood levels, or reduces the patient's exposure, to the medication, decreasing its effectiveness.
"Thus, the reduction in blood levels caused by St. John's Wort may cause Gleevec® to be less effective, resulting in treatment failure," Smith said. "The other thing that can happen is that, if blood levels are too low, the leukemia cells also can become resistant to Gleevec®, rendering it completely ineffective, even if the dose is increased."
Similar results have been described in drug interaction studies of St. John's Wort with medications for AIDS, said Smith, who added that he believes cancer patients should avoid herbal supplements in general during treatment.
"It is imperative that patients know that herbals are not FDA regulated and that they may be very dangerous when combined with certain drugs. Patients should always check with their physicians or pharmacists before taking any herbal or over the counter product. Their lives literally may depend on it," Smith said.