Tamoxifen Interactions

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
Bupropion                     Wellbutrin
Chloroquine                   Aralen
Chlorpheniramine           Alernine, Chlor-trimetron          
Chlorpromazine             Thorazine            
Cinacalcet                    Sensipar
Diphenhydramine           Benadryl, Dytan Suspension, Dytan-D Suspension, Sominex Formula
Duloxetine                     Cymbalta
Fluoxetine.                    Prozac, Serafem
Haloperidol                    Haldol
Halofantrine                   Halfan      
Imatinib                         Gleevec
Paroxetine                     Paxil, Pexeva
Perphenazine                Trilafon
Propafenone                  Rythmol
Propoxyphene               Darvon, Darvon-N  
Quinidine                      Duraquin, Dura-tabs, Quinaglute, Quinidex                
Terbinafine                    Lamisil
Thioridazine                  Mellaril

[zouzi]

Thank you Bluebutterfly for this excellent article, I know quite a few friends who are on Tamoxifen or  Arimidex and are actually taking antidepressant...I'll make sure to Email them your article so they can discuss it with their doctor..Thanks again..Sue.

[alidi]

Thanks for a very complete info. It is great to communicate with you all. I am learning a lot, even if every case is different. God Bless, Alidi

[katarina777]

Thank you so much BB2222. It's really great to have you provide this information. Do you know what other blood pressure meds may be listed? Because I take three different kinds.

I also heard, and don't know how much value is to it, but that if you have strong side effects from Tamoxifen it seems more likely that it is working? Like bad hot flashes.

[bluebutterfly2222]

Hi Kat!

There wasn't room to paste the whole article (and the parts I included ended up mangled for some reason), but it also discussed more about some people having a gene deficiency that makes them unable to metabolize  CYP2D6.

This was the article's recommendation:

"What You Can Do?
If you are a candidate for tamoxifen
therapy to treat breast cancer,
talk with your physician about the
CYP2D6 issue. If CYP2D6 testing
is needed but is not covered by your
insurance you may consider trying to
pay for it out of pocket.
If you are a candidate for tamoxifen
(or are already taking tamoxifen),
avoid taking any of the CYP2D6
inhibitors listed in the Table. Also,
check all of the other medications you
take to make sure that they are not
CYP2D6 inhibitors. Most pharmacists
have sources of information
that provide information on which
drugs affect which drug metabolizing
enzymes."

Warmest regards,
bluebutterfly

[valliboy]

Hi:
I loved your article post. I didn't see anything about Pristiq. That is the anti D. I am on. Ever heard of it?

[bluebutterfly2222]

Pristiq is in the same class of antidepressants (the SNRIs) as Effexor, so that may be a favorable sign, but if you do end up on tamoxifen,  I'd check with a pharmacist to be sure of its individual CYO2D6 inhibition effect.

Give Valentine some hugs and kisses for me, okay? :-)

Regards,
bluebutterfly

[bluebutterfly2222]

Oooooops, typo! That should be CYP2D6, of course...

[SueYoung55]

This is absolutely wonderful information that should be printed for each person on tamoxifen! Drug interactions are so important and if you're taking one thing that's stopping the other from working properly, you need to know it and make changes!

Great job!!!!!