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21 January 2005
Antidepressants Hinder Effectiveness Of Tamoxifen 
A large clinical trial has confirmed data from an earlier study showing that selective serotonin reuptake inhibitor (SSRI) antidepressants may hinder the effectiveness of tamoxifen, a drug commonly administered to breast cancer patients. The study, published in the Journal of the National Cancer Institute, also reports that researchers now have pinpointed genetic types that are linked with this effect. The researchers, led by David Flockhart of Indiana University, 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. We have withheld clinical recommendations, because at this point we don't have final data," said Flockhart. 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. "We can see the light at the end of the tunnel. 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," said Flockhart.
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