We have long reported on the dangers associated with certain antidepressants, with some linked to pediatric suicides, others to cardiac deaths in women. Now, Bloomberg.com is reporting on the findings of a new study that indicate the breast cancer medication tamoxifen does not work when taken with certain antidepressants, resulting in an increased risk of breast cancer recurrence.

The study cited Prozac (Eli Lilly and Company), Zoloft (Pfizer Inc.), and Paxil (GlaxoSmithKline), said Bloomberg.com, and indicated that breast cancer tumors were over twice as likely to come back following two years of antidepressant use while on tamoxifen, versus those taking tamoxifen alone. The research was conducted by Medco Health Solutions Inc., and was just presented at an American Society of Clinical Oncology meeting in Florida. The study involved 945 women taking tamoxifen, and another 353 taking tamoxifen and an antidepressant.

The study found that patients on both an SSRI and tamoxifen experienced a 14 percent risk of tumor return, versus a 7.5 percent increase for women on tamoxifen alone. The risk jumped to 16 percent with Paxil, Prozac, or Zoloft users, said Bloomberg.com. “This is the first large outcomes-based study to reinforce earlier research questioning the use of Paxil and Prozac in patients taking tamoxifen,” said Robert Epstein, quoted Bloomberg.com. Epstein is a study author and chief medical officer for the pharmaceutical benefits firm Medco.

Treating hot flashes with antidepressants is an unapproved use. Following a seven-year study in the United States, hormone replacement therapy (HRT)—the typical medical treatment for hot flashes—was linked to an increase in breast cancer and heart attacks, explained Bloomberg.com. Because of this, doctors started treating flashes with antidepressants. Hot flashes are a side effect of tamoxifen, said Bloomberg.com.

Interestingly, external science advisers to the U.S. Food and Drug Administration (FDA) looked at the effect of some antidepressants on the effects of tamoxifen, specifically if antidepressants destroyed tamoxifen’s efficacy, said Bloomberg.com. The 2006 review concluded that data on the effect should be added to tamoxifen labeling; however, to date, there is no such statement on this risk on the medication’s label, said Bloomberg.com.

According to the U.S. Centers for Disease Control and Prevention (CDC), said Bloomberg.com, breast cancer is the second most common female cancer, with 187,000 women diagnosed and 41,000 women dying from it in 2005, the last year for which CDC data are available.

In the body, tamoxifen works by combining with CYP2D6, a liver enzyme; the combination becomes endoxifen a known tumor fighter, said Bloomberg.com. Certain antidepressants also use CYP2D6, which inhibits tamoxifen’s efficacy, said Bloomberg.com. “The patient might as well be taking a placebo,” said Frankie Ann Holmes, associate director of breast cancer studies at U.S. Oncology Research in Houston, quoted Bloomberg.com citing a 2005 report published by ASCO.

Holmes said antidepressants known as selective serotonin reuptake inhibitors (SSRIs)—for instance, Paxil, Prozac, Zoloft, Celexa, and Lexapro—are known to cause the interaction, reported Bloomberg.com, which added that Paxil most powerfully blocks the CYP2D6 enzyme. Patients taking tamoxifen should not be taking or prescribed SSRIs, said Holmes.

This entry was posted on Monday, June 1st, 2009 at 10:17 am and is filed under Pharmaceuticals.