Ever wonder why a certain medication may work great for a friend and do nothing for you?  One reason could be your genes.

Let’s take fexofenadine (Allegra) for example.  You have watery eyes and a drippy nose during spring allergy season and pop an Allegra.  There is a lot that goes on in your body before that medication brings about allergy relief.  It has to dissolve, be absorbed, get transported to the cells where it is going to act — and it has to stay inside of those target cells.

Staying inside the cells instead of the medicine being transported back out again is where genetics comes in to play.

Some medications and other toxins are transported back out of cells by an ATP-binding cassette transporter protein encoded by the ABCB1 gene.  In the epithelial cells that line your intestines, the ABCB1 proteins are involved in pumping substances back into the intestinal lumen.  So imagine if you take an Allegra, it dissolves, gets absorbed, and then part of that gets pumped back into the intestines to be eliminated. Genetic variants in ABCB1 affect how much stays in the cells vs getting eliminated (through intestines, bile, urine).

In general, it seems like a good thing for the body to get rid of a substance that it thinks might be toxic. While an allergy medication not working quite as well is not that big of a deal, the real problem comes in when trying to keep chemotherapy drugs inside of cancer cells in order to act upon them.  This gene has been studied in depth for cancer treatment drugs.

ABCB1 gene (multidrug resistance protein, p-glycoprotein):

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