NEW YORK (Reuters Health) - St. John's wort, an herbal medicine used to treat
depression, may also reduce the effect of a commonly-used chemotherapy drug
called irinotecan, according to a study of a small number of patients.
Dr. Alex Sparreboom of the Erasmus MC-Daniel den Hoed Cancer Center in the
Netherlands and his colleagues discovered that when five cancer patients
received both irinotecan and St. John's wort, the levels of the active form of
irinotecan in the body decreased by 42%, relative to irinotecan given alone.
Furthermore, Sparreboom and his colleagues note, St. John's wort combined
with irinotecan appeared to reduce the cancer drug's ability to suppress bone
marrow cells, a potentially toxic side effect of the treatment that increases
patients' susceptibility to infections.
Although St. John's wort may help cancer patients combat mild depression and
the toxic effects of chemotherapy, the treatment may also impair the ability of
irinotecan to adequately rid the body of cancer, the authors note.
"Overall, our findings suggest that irinotecan metabolism and toxicity are
altered by St. John's wort and that the two agents cannot be given safely in
combination without compromising overall antitumor activity," Sparreboom and his
team write.
According to the report in the August 21st issue of the Journal of the
National Cancer Institute, Sparreboom and his colleagues gave irinotecan to five patients with
either sarcoma, colorectal cancer, or lung cancer. After a few weeks of
treatment, patients began to take 300 milligrams of St. John's wort three times
per day, which they continued for the remainder of the trial.
In an interview with Reuters Health, Sparreboom explained that irinotecan
first enters the body as an inactive molecule. The molecule then needs to be
turned into a compound known as SN-38 in order to exert its anti-cancer effects.
However, before that activation occurs, liver enzymes can step in and change
the chemical properties of irinotecan, and also render it less able to destroy
cancer cells. Treatment with St. John's wort can increase the levels of one of
these particular enzymes, known as CYP3A4.
Consequently, other chemotherapy drugs that can be affected by CYP3A4 may
also exhibit lower effects in the presence of St. John's wort, Sparreboom added,
such as paclitaxel, docetaxel, and tamoxifen.
In addition, he noted, other substances that either raise or lower levels of
CYP3A4 may also affect the ability of chemotherapy drugs to kill cancer cells,
substances which include garlic supplements, ginkgo biloba, ginseng, and kava.
"Although not yet studied in relation to chemotherapy drugs, healthcare
professionals should ask their patients about the use of herbal products, and
should seriously consider the possibility of potentially life-threatening
interactions," Sparreboom said.
In an accompanying editorial, Drs. Patrick J. Mansky and Stephen E. Straus of
the National Institutes of Health in Bethesda, Maryland write that surveys show that cancer patients
may be more likely than others to turn to alternative therapies. However, the
current findings, along with those from other studies, suggest that patients
should use complementary and alternative medical (CAM) treatments with caution,
the authors note.
"It would be prudent for patients and their oncologists to appreciate that,
no matter how beneficial some approaches may appear to be, they are not all
safe," Mansky and Straus write.
"Together, patients and oncologists should consider the options and develop a
plan regarding which CAM practices to pursue and which to put aside altogether,"
they add.
