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Antidepressants Can Make Cancer Pills Ineffective

May 31, 2009

New research shows that breast cancer survivors risk having their disease come back if they use certain antidepressants while also taking the cancer prevention drug tamoxifen.

Close to 500,000 women in the United States take tamoxifen, which cuts the chances of getting breast cancer again in half.  Quite a few of them also take antidepressants for hot flashes, because hormone pills are not considered safe after breast cancer.

Doctors have known for a while that antidepressants and other medicine lowers the amount of tamoxifen’s active form in the bloodstream.  But the affect on cancer risk is unknown.

However a new study that was reported on Saturday at a cancer conference in Florida is the largest to look at the issue.  The results showed that using these interfering drugs, including Prozac, Paxil or Zoloft, can virtually wipe out the benefit tamoxifen provides.

Doctors question the magnitude of harm from combining the medicines, and a smaller study suggests it may not be that big of an impact.

It is evident that not all antidepressants pose this problem, so women should talk to their doctors about which ones are best.

“There are other alternatives we can consider” that are safer, said Dr. Eric Winer, breast cancer chief at the Dana-Farber Cancer Center in Boston.

Winer had no role in the study, which was done by Medco Health Solutions Inc., a large insurance benefits manager.  The research team used members’ medical records to identify 353 women taking tamoxifen, plus other drugs that might interfere with it, and 945 women taking tamoxifen alone.  The women taking a drug combination did so for about a year on average.

Researchers then checked to see how many were treated for a second cancer occurrence.  There were other occurrences in 7 percent of the women taking tamoxifen alone, and then 14 percent of the women taking other drugs that might interfere.

Dr. Robert Epstein, Medco’s chief medical officer, said that if women want to take an antidepressant, “you probably want to stay away from those three.”

Epstein said that no greater beast cancer risk was seen in women taking the antidepressants Celexa, Lexapro or Luvox with tamoxifen, and there are reasons to think that other antidepressants may be safe as well.

Another study, led by Dr. Vincent Dezentje of Leiden University Medical Center in the Netherlands, found little risk from combining tamoxifen and popular antidepressants.  But only 150 women that took part in the study took the pill cocktail for over two months, and they were compared to women taking combinations for a shorter times.

The federal Food and Drug Administration is considering changing tamoxifen’s warning label to warn about the antidepressant drugs and a gene variation some women have that might make the drug less effective.

“This is a very controversial area,” said Dr. Claudine Isaacs, a breast specialist at Georgetown University’s Lombardi Comprehensive Cancer Center. “Until these data are absolutely clear, I would avoid drugs that impact on tamoxifen metabolism.”

Breast cancer is the most common cancer in American women, with over 182,000 new cases diagnoses last year that caused nearly 41,000 deaths.

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