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Tamoxifen & Zoloft bad cocktail

Posted Oct 18 2009 10:00pm

New Study: Antidepressants Commonly Prescribed with Tamoxifen Put Women at Much Higher Risk for Recurrent Breast Cancer:

- Several SSRIs more than double risk of cancer recurrence in tamoxifen
treated patients

- Nearly 30 percent of tamoxifen users take drugs that reduce its
effectiveness against breast cancer

ORLANDO, Fla., May 30 /PRNewswire-FirstCall/ -- An important new study finds
that certain popular antidepressants frequently prescribed to women taking the
breast cancer drug tamoxifen more than double the risk of a breast cancer
recurrence for those using both medications. The research presented by Medco
Health Solutions, Inc. (NYSE: MHS) and Indiana University School of Medicine
at the 2009 Annual Meeting of the American Society of Clinical Oncology (ASCO)
is the largest study to date looking at how these drugs impact breast cancer
recurrence rates when taken with tamoxifen.

The antidepressants at issue are three widely used selective serotonin
reuptake inhibitors (SSRIs), Prozac(R) (fluoxetine), Paxil(R) (paroxetine) and
Zoloft(R) (sertraline), and are among a group of drugs known as CYP2D6
inhibitors. Antidepressants are often prescribed with tamoxifen to treat
depression - a common co-morbidity of the disease, as well as hot flashes - a
common side-effect of the breast cancer drug.

The three drugs that pose this risk for women on tamoxifen are considered to
be moderate to potent CYP2D6 inhibitors. Several other SSRIs examined in the
study that are weak CYP2D6 inhibitors did not raise breast cancer recurrence
risks for patients using them along with tamoxifen. Those SSRIs included
Celexa(R) (citalopram), Lexapro(R) (escitalopram) and Luvox(R) (fluvoxamine).

"We've known that these CYP2D6 inhibitor drugs block the activation of
tamoxifen chemically, but this is the first time there's evidence that these
drugs are putting women at a much higher risk for recurrent breast cancer,"
said Dr. Robert Epstein, Medco's chief medical officer and one of the study
researchers. "It's also the first time that a comparative analysis has been
done looking at various SSRIs and what's clear is that several of these drugs
are extremely risky for women to take with tamoxifen, while others don't
present a problem."

This study advances prior research which has shown that the active form of
tamoxifen, called endoxifen, is found in far lower levels in the blood stream
when CYP2D6 inhibitor drugs are present, and it is the first study to show the
comparative impact of various antidepressants on breast cancer recurrence.

"While we expected to see some impact on the disease recurrence rate based on
already existing evidence, what is remarkable is that the effect is consistent
with the pharmacologic potency of these antidepressants as CYP2D6 inhibitors.
This lends biological plausibility to the data," added Dr. David Flockhart,
chief of clinical pharmacology at Indiana University School of Medicine and a
member of the research team.

Study Details
The study was a retrospective analysis of almost 1,300 women who were newly
prescribed tamoxifen to treat breast cancer between 2003 and 2005 and were
monitored for at least two years, with the average being 2.7 years. All study
patients had to be at least 70 percent compliant with their tamoxifen therapy
and on average, compliance was 90 percent throughout the study period. The
average duration that patients used tamoxifen and a CYP2D6 inhibitor
concurrently was 340 days.

The analysis first looked at two different cohorts, one with 353 women, about
27 percent of the study sample, who were taking a moderate to potent CYP2D6
inhibitor in conjunction with tamoxifen which included but was not limited to
antidepressants, and a group of 945 women on tamoxifen who were not taking any
CYP2D6 inhibitor. The patients' pharmacy and medical records were analyzed to
determine the medications used and the incidence of a breast cancer
recurrence. Comparisons were made between the cohorts using a CYP2D6
inhibitor and the group on tamoxifen only. The study found that women taking
a moderate to strong CYP2D6 inhibitor had a two-year breast cancer recurrence
rate of 13.9 percent, 1.9 times higher than the 7.5 percent recurrence rate of
those only using tamoxifen.

Given that 60 percent of the women in the study on a CYP2D6 inhibitor were
using an SSRI, the researchers examined a subset that included only those
patients taking an SSRI and divided it into two cohorts, one that included 213
women on a moderate to potent CYPD2D6 inhibitor SSRI, and one made up of 137
women using a weak CYP2D6 inhibitor SSRI.

Results showed an even greater increase in the risk of a recurrence among
those taking a moderate to potent CYP2D6 inhibitor SSRI as compared to the
initial analysis. These women had a rate of breast cancer recurrence of 16
percent, 2.2 times higher than women only taking tamoxifen. Patients using
SSRIs that are weak CYP2D6 inhibitors had a disease recurrence rate of 8.8
percent and were not at any increased risk for the disease.

"Since the majority of women using a CYP2D6 inhibitor were taking an SSRI, we
felt it was incumbent upon us to look specifically at that drug class," said
Epstein. "What we found is that the choice of which SSRI is prescribed could
make a huge difference in whether there's a recurrence of the disease. That's
very important information for breast cancer patients and their physicians."

Tamoxifen is one of the oldest and most widely used treatments for reducing
the risk of breast cancer recurrence among women with estrogen-dependent
tumors. The drug works by blocking the estrogen receptors in the breast cells
and can reduce the risk of a breast cancer recurrence by up to 50 percent.
It's the only anti-estrogen available for prevention of breast cancer
recurrence in pre-menopausal women and is one of several anti-estrogens used
to treat post-menopausal breast cancer patients. Approximately 500,000 women
take tamoxifen in the U.S., with 80,000 new patients starting on the treatment
annually. Nearly 30 percent of women taking tamoxifen also use an

Alerting Physicians
While evidence has been mounting that CYP2D6 inhibitors can reduce the
effectiveness of tamoxifen, many physicians treating breast cancer patients
are still unaware of the problem or may not know that their patient has been
prescribed a strong inhibiting antidepressant by another physician. In an
effort to ensure that women get the full benefit of tamoxifen, Medco has been
alerting physicians when a patient has been prescribed both tamoxifen and a
moderate or potent CYP2D6 inhibitor antidepressant.
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