St. John's wart weakens punch of cancer drug

Monday, April 8th 2002, 12:00 am

By: News On 6

SAN FRANCISCO (AP) _ St. John's wort appears to interfere powerfully with a common cancer drug and can reduce its punch for weeks after people stop taking the herbal supplement, a study shows.

St. John's wort is often taken as an over-the-counter remedy for mild depression, though its effectiveness has been questioned. Doctors also know the herb can interfere with the body's use of a variety of other medicines.

In a small study released Monday, doctors showed that St. John's wort decreases blood levels of one chemotherapy drug by about 40 percent. This effect lingered for more than three weeks after people stopped taking the supplement.

Dr. Ron Mathijssen of the Rotterdam Cancer Institute in the Netherlands, who directed the study, said St. John's wort could reduce the ability of chemotherapy to knock down cancer.

``People don't realize it is a drug because you don't need a prescription. People think it's harmless,'' he said.

Mathijssen presented the results of the study, conducted on five patients, at a meeting in San Francisco of the American Association for Cancer Research.

Despite the small size of the study, experts said the findings are believable because they fit with earlier reports showing that St. John's wort can disrupt drug treatment.

Two years ago, the Food and Drug Administration warned that the herb can interfere with protease inhibitors, drugs that are widely used to treat AIDS.

In the latest study, researchers tested the interaction of St. John's wort with Camptosar, a medicine used to treat many kinds of cancer.

Use of supplements is common in cancer patients. Some studies suggest that about half of them use vitamins and other over-the-counter treatments in hopes of improving their chances of beating the disease.

``We are very concerned in the medical community about the drugs our patients are taking that we don't know about,'' said Dr. Karen Antman of New York Presbyterian Hospital. ``I make it a point to ask, but I'm not sure my patients always tell me the truth.''

St. John's wort interferes with an enzyme called P450 that the body uses to break down about half of all drugs. Because of this, St. John's wort is believed to inhibit many of the most widely prescribed medicines. Among others are digoxin and beta blockers used for heart disease, seizure medicines and drugs used to prevent organ rejection after transplants.