Several of us have posted in recent months about the importance of using care in selecting an antidepressant, because certain ones can reduce the effectiveness of tamoxifen.
I just came across an artricle in Worst Pills, Best Pills News (March 2009) which warns that a numder of other medications can also block the effectiveness of tamoxifen. I will paste some excerpts from the article below:
Watch Out For Interactions with Tamoxifen (Nolvadex)
Breast cancer is the most common cancer in women and tamoxifen (NOLVADEX ) is used commonly in the treatment and sometimes in the prevention of this disease. In 2007, 1.7 million prescriptions were filled for tamoxifen.
However, recent evidence suggests that certain other drugs can reduce the anti-cancer effects of tamoxifen,
potentially increasing cancer recurrence and reducing survival. Certain antidepressants, such as fluoxetine
(PROZAC), paroxetine (PAXIL) and bupropion (WELLBUTRIN), could reduce the effect of tamoxifen because
they are among the most potent CYP2D6 inhibitors.
Why are drug interactions a problem for tamoxifen?
Tamoxifen is a "prodrug," which means that the drug molecules in the medication itself are inactive; they
must be transformed by the body to the active molecules that actually produce the beneficial effects. The
enzyme that activates tamoxifen is CYP2D6.Some people may have a genetic CYP2D6 deficiency that may interfere
with the effectiveness of tamoxifen.
What drugs may reduce the effect of' tamoxifen?
Among the most important CYP2D6 inhibitors are antidepres- . sants, because patients with breast
cancer may be taking these medications. Fluoxetine, paroxetine and bupropion are at the top of the list
of drugs to watch out for. Other antidepressants are weaker inhibitors of CYP2D6, such as sertraline
(ZOLOFT, escitalopram (LEXAPRO) and citalopram (CELEXA), while still others have little or no
effect on CYP2D6 such as venlafaxine (EFFEXOR). Although the problem of using antidepressants with tamoxifen has received the most attention in the medical literature, keep in mind that many other medications also inhibit CYP2D6: heart drugs, antifungal agents, analgesics and even antihistamines such as diphenhydramine
(Note that the accompanying Table includes only those drugs with substantial inhibition of CYP2D6. Many
other drugs are moderate to weak inhibitors of CYP2D6, and, depending on the dose of the drug, they could
potentially inhibit the conversion of tamoxifen to its active forms.)
Table 1. Drugs That Inhibit CYP2D6
Drug Brand Name
Amiodarone Cordarone, Pacerone
Chlorpheniramine Alernine, Chlor-trimetron
Diphenhydramine Benadryl, Dytan Suspension, Dytan-D Suspension, Sominex Formula
Fluoxetine. Prozac, Serafem
Paroxetine Paxil, Pexeva
Propoxyphene Darvon, Darvon-N
Quinidine Duraquin, Dura-tabs, Quinaglute, Quinidex