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Common Antidepressants Lower Effects of Tamoxifen in Many Women
20 Jan 2005
INDIANAPOLIS - Additional evidence that a class of antidepressants can reduce
the effectiveness of tamoxifen has been published by researchers from the
Indiana University School of Medicine, the University of Michigan and Johns
Hopkins University.
Results of the trial are published in the current
issue of the Journal of the National Cancer Institute.
The large
clinical trial confirmed data from an earlier study showing that selective
serotonin reuptake inhibitor antidepressants may hinder the effectiveness of
tamoxifen, a drug commonly administered to breast cancer patients. The study also reports that
researchers now have pinpointed genetic types that are linked with this effect.
Led by David Flockhart, M.D., Ph.D., an IU professor of medicine and
director of the Division of Clinical Pharmacology, the researchers examined the
effects of SSRIs in women who were prescribed tamoxifen to treat the common side
effects of breast cancer therapy which include depression and hot flashes.
More than a fourth of the women enrolled in this study were prescribed
SSRIs. The study showed that the various SSRIs taken by the women have different
effects on the amount of active tamoxifen byproducts in their blood.
"This is important because previous studies have shown that when
tamoxifen is broken down, the resulting molecules are extremely powerful at
blocking estrogen receptors and thereby exert a cancer-inhibitive effect," said
Dr. Flockhart.
"We have withheld clinical recommendations, because at
this point we don't have final data," said Dr. Flockhart. The study makes clear
that knowledge of a drug's ability to inhibit CYP2D6 enzyme activity may help
clinicians anticipate important drug interactions. Genetic testing may help
identify a group of women who may experience greater benefit from tamoxifen or
those who may benefit more from one SSRI than another,” he said.
This
study is the first large-scale clinical trial to determine the influence of
multiple genetic variations and drug interactions on the plasma concentrations
of tamoxifen and its active metabolites.
"We can see the light at the
end of the tunnel," said Dr. Flockhart. "Using our pharmacogenetic tool kit, we
are very close to being able to identify which women should be given which drug
to treat her depression or hot flashes."
This study was funded by the
Pharmacogenetics Research Network of the National Institutes of Health.
Contact: PR Staff
317-274-7722
caisen@iupui.edu
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