Cancer treatment could be weakened by St John's Wort - study

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Related tags: St john, Chemotherapy

St John's Wort is a popular herbal treatment used by millions to
combat depression, but a new study from the Netherlands suggests
that it could in fact have an adverse effect on chemotherapy drugs
used by cancer patients.

St John's Wort is a popular herbal treatment used by millions to combat depression, but a new study from the Netherlands suggests that it could in fact have an adverse effect on chemotherapy drugs used by cancer patients.

The Dutch researchers, led by Dr Ron Mathijssen of the Rotterdam Cancer Institute, said that St John's Wort stimulated an enzyme which speeds up the metabolism of many drugs, including the cancer fighter irinotecan, sold under the brand name Camptosar. Because of this, the supplement can substantially reduce the cancer-fighting effects of the drug.

Speaking at the annual meeting of the American Association for Cancer Research in San Francisco, California, Mathijssen said: "Since about 50 per cent of all drugs are metabolised by this enzyme, the combination effect we found with St John's Wort and irinotecan might occur with many other anti-cancer agents, so the problem is potentially more widespread than this study shows."

The researchers studied a group of five cancer patients, some of whom were given a course of irinotecan followed three weeks later by a second course combining irinotecan with St John's Wort, while the rest were given the combination first and then the anti-cancer drug on its own.

They discovered that when the drug was combined with the plant extract, its availability in the body was reduced by some 40 per cent. Furthermore, the effects of St John's Wort lasted much longer than the three week period during which patients were given the combination, showing that simply stopping supplementation with the product prior to using irinotecan is not enough.

"We do not know at this time how long patients should stop using St John's Wort before being treated with irinotecan as our study was not long enough to make such a determination,"​ Mathijssen said.

Related topics: Research

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