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Antidepressants May Hinder Tamoxifen

Some SSRIs May Reduce Effectiveness of Breast Cancer Prevention

WebMD Health News

Dec. 2, 2003 -- Taking an antidepressant prescribed to combat a common side effect of the breast cancer prevention drug tamoxifen may actually decrease its effectiveness in preventing the disease.

A new study shows that the antidepressant Paxil interferes with the breakdown of tamoxifen into its active anticancer ingredients within the body. Researchers say findings raise the possibility that the new generation of antidepressant drugs, known as serotonin reuptake inhibitors (SSRIs) may reduce the effectiveness of tamoxifen therapy.

Researchers say hot flashes occur in about 80% of women who take tamoxifen. Doctors often prescribed the drug after breast cancer treatment to reduce the recurrence of breast cancer or give it to high-risk groups to prevent breast cancer. SSRIs are often used as an alternative to hormone replacement therapy to combat hot flashes in women taking tamoxifen.

SSRIs May Interfere With Tamoxifen Treatment

In the study, which appears in the Dec. 3 issue of Journal of the National Cancer Institute, researchers examined the effect of Paxil on the metabolism of tamoxifen in blood samples from 12 women with breast cancer who were being treated with tamoxifen.

They found that Paxil appeared to inhibit the breakdown of tamoxifen into its active form which acts as a potent antiestrogen to help fight breast cancer.

In addition, the study showed that four weeks of treatment with Paxil in conjunction with tamoxifen also reduced the concentrations of another anticancer component that was present in much higher concentrations before the women received the antidepressant.

Too Soon to Change Recommendations

Although the findings indicate that SSRIs may interfere with how the body breaks down tamoxifen, researchers say more research is needed in larger numbers of women to determine whether these effects have an impact on the drug's effectiveness in preventing breast cancer.

In an editorial that accompanies the study, Matthew P. Goetz, MD, and Charles L. Loprinzi, MD, of the Mayo Clinic in Rochester, Minn., agree that further studies are needed before recommendations against using tamoxifen and SSRIs together are made.

The editorialists say that the practical implications of this study will remain unclear until those results are known. They also note that the effects of each of the newer antidepressants on tamoxifen metabolism may also vary.

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