Paxil Blocks Tamoxifen, Lowers Survival Odds Against Breast Cancer

Patients should avoid taking the two drugs together, researchers say

By Steven Reinberg
HealthDay Reporter

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MONDAY, Feb. 8 (HealthDay News) -- Women with breast cancer who take both tamoxifen and the antidepressant Paxil may increase their risk of dying because Paxil reduces tamoxifen's effectiveness, Canadian researchers report.

"Paxil can deprive women of the benefit of tamoxifen, especially when it is used in combination with tamoxifen for a long time," said lead researcher Dr. David Juurlink, division head of clinical pharmacology and toxicology at Sunnybrook Health Sciences Center in Toronto.

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"Patients who are on tamoxifen and who require an antidepressant should probably be given something different," he added.

Paroxetine (Paxil) is a selective serotonin reuptake inhibitor (SSRI) that significantly inhibits an enzyme called cytochrome P450 2D6, which is needed to metabolize tamoxifen into its active form. But this dampening effect was not seen with certain other SSRIs evaluated, including citalopram (Celexa) and venlafaxine (Effexor), the researchers said.

Patients taking Paxil and tamoxifen should talk with their doctors about changing their antidepressant, Juurlink said.

But he advised against abruptly discontinuing Paxil.

"There is a very real danger to stopping Paxil suddenly. There is a well-described withdrawal syndrome and the risk of depression becoming more severe," he said.

In addition, any transition to another antidepressant should be done gradually over several weeks, he said.

The report is published in the Feb. 8 online edition of the British Medical Journal.

For the study, Juurlink's group looked at the medical records of 2,430 women with breast cancer who began taking tamoxifen between 1993 and 2005. About 30 percent of the women were also taking an antidepressant, Paxil being the most common. Antidepressants are often prescribed to reduce hot flashes associated with tamoxifen in addition to easing symptoms of depression.

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