St. John's Wart Blunts Cancer Therapy
Cancer patients
who use St. John's wort -- the over-the-counter preparation touted as an
alternative medication for numerous ills including depression -- may compromise
certain cancer treatments, researchers said.
"Our limited
study indicated that St. John's wort and the anti-cancer drug irinotecan
cannot be given in combination," said Dr. Ron Mathijssen, a pharmacology
researcher at the Rotterdam Cancer Institute in the Netherlands.
Mathijssen
said experiments in five patients undergoing treatment for lung, colon
and other malignancies found when the two drugs are taken together, patients'
exposure to the active anti-cancer ingredient in irinotecan decreases by
40 percent.
Mathijssen
disclosed the finding in a presentation at the annual meeting of the American
Association for Cancer Research.
The research,
he said, suggests tumors receive less cancer-killing drug, a situation
that might blunt the effects of treatment. Mathijssen explained because
the study was small and limited to a nine-week period it was difficult
to assess whether the outcomes for the patients were affected by taking
St. John's wort.
He said, however,
it was worrisome enough that to perform a long-term study "would be considered
unethical because of the possible harm to the patients."
"The take home
message from this study," said Dr. Karen Antman, professor of medicine
and pharmacology at Columbia University in New York, "is that these food
additives or nutriceuticals are drugs. We are concerned about their interactions
with chemotherapeutic medicines."
She said patients
using alternative medications to fight cancer -- and she estimated about
half of cancer patients do that -- should inform their doctors if they
are taking any over-the-counter medications.
"I do ask my
patients if they are taking these products," Antman said, "but I'm not
sure if they are telling the truth."
She said it is incumbent
upon doctors to communicate about the use of the over-the-counter herbals
with their patients. She admitted, however, "some doctors communicate better
than others."
Antman said
the same metabolic pathway used by St. John's wort and irinotecan also
is employed by other common anticancer drugs such as cyclophosphamide,
which is used in breast cancer, leukemia and other diseases.
"About 50 percent
of all drugs are metabolized through this pathway," Mathijssen said, "so
the combination we found in this study might occur with many other anticancer
agents. So the problem is potentially more widespread than this single
study shows."
The study also
indicated St. John's wort effects irinotecan metabolism for some time after
the herbal remedy is discontinued.
"This means
people have to realize that it's not just good enough to stop using St.
John's wort just prior to treatment with irinotecan," Mathijssen said.
He measured
effects of St. John's wort for longer than three weeks after it was stopped.
Exactly how long the effect lasts, he said, is not yet known.
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Copyright 2002 by United
Press International.
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