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Lamisil, Tamoxifen Drug-to-Drug Interaction

05/21/2012      Craig Herman, DPM


I learned something new today that I think all podiatrists should know. About 6 weeks ago, I started a patient on Lamisil. Our electronic record system (E-Clinical Works) checks for any interactions between medications and no warnings were issued. The patient came back today for her 6 week visit, at which time I planned on drawing blood for hepatic function and a CBC. The patient proceeded to tell me that her oncologist told her to stop taking the Lamisil immediately because it would decrease the effect of Tamoxifen by interfering with how the body activates Tamoxifen.

I found this very disturbing and potentially very dangerous. We had always learned about the effects of inhibiting CYP450. It had been drilled into our heads about the potential drug to drug interactions with Warfarin and SSRI's. There is nothing in the package insert specifically identifying Tamoxifen itself as a problem. However, after doing some research, I found out that Lamisil can also inhibit CYP2D6, necessary for Tamoxifen. As soon as I Googled the two drugs, I found a number of articles stating this.

Next, I called four colleagues who are very intelligent, have been practicing for over 10 years, prescribe Lamisil often, and whose opinion I really trust. Not one of them has ever heard of this drug to drug interaction. My question to other podiatrists out there is, have you ever herd of this interaction? If yes, why do so many other respected podiatrists not know about it and either way how do we get the word out? It is not a potential life-altering and threatening complication. If the effects of Tamoxifen are reduced, the breast cancer can recur. I would appreciate any input/knowledge that other podiatrists have about this drug to drug interaction.

Craig Herman, DPM, NY, NY, foothealer@aol.com