- Fluoxetine and Tamoxifen

Fluoxetine and Tamoxifen

Posted about 1 year ago by David Chan (HIGH significance )

Affecting Drugs

N06AB03 Fluoxetine
N06AB05 Paroxetine

Effect

Inhibits

Affected Drug

L02BA01 Tamoxifen

Details

The antidepressant paroxetine interferes with the metabolism of tamoxifen, leading to increased breast cancer mortality, BMJ reports online. Another SSRI, fluoxetine, is suspected of having the same effect.

Researchers in Toronto retrospectively tracked breast cancer mortality in some 2500 women receiving tamoxifen plus an SSRI during some part of their tamoxifen regimen. They found that as paroxetine use increasingly overlapped with tamoxifen, breast cancer mortality increased as well. Compared with women with minimal treatment overlap, those overlapping 25%, 50%, and 75% of the time had corresponding increases in cancer mortality of 24%, 54%, and 91%.

The authors estimate that there would be one additional breast cancer death for every 20 women with treatment overlaps of 41%, and one extra death for every 7 women overlapping 100%.

The effect, the authors speculate, stems from paroxetine's interference with converting tamoxifen to an active metabolite. Fluoxetine, which interferes in the same manner, showed no adverse effect, possibly owing to the small number of women taking it in this sample. Editorialists write: "A switch to an antidepressant with low or no ... inhibitory activity should be considered."

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