PLAVIX GENETICS

May 28, 2010

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

Have you heard Trevor on the radio? Listen to 730 CKDM Tuesday Mornings at 8:35 am! We now have most of the articles published in the Parkland Shopper on our Website www.dcp.ca

The information in this article is intended as a helpful guide only. It is not intended to be used as a substitute for professional advice. If you have any questions about your medications and what is right for you see your doctor, pharmacist or other health care professional.

On the Origin of Species was published over 150 years ago by Charles Darwin. It laid out his theory of evolution.

Darwin actually published many papers, and books over his career. He was a barnacle expert and spent a lot of time breeding plants. In his green house he determined that you got better, stronger plants if you cross-fertilized them than if you self-fertilized them. Remember, Darwin had no idea what DNA or genes were or that you could pass your genes on to your off-spring. But when he saw that during breeding it is better to cross breed than to put close relatives together, this made him worried about his own children. You see, Darwin married his first cousin, Emma Wedgwood. A recent study of Darwins family tree showed a higher than expected inbreeding coefficient. That means his offspring were more likely than average to have two identical copies of a gene. All genes come in pairs. Most bad genes are what we call recessive. That means if you have one copy of the bad gene and one good gene, the good gene will win out and you will not develop the bad trait. However, if you have two identical genes, and they are both for a bad trait, you will get that bad trait. If you marry your first cousin, your children are more likely to have two identical bad genes than the general population. So your children are more likely than average to have genetic diseases.

Speaking of genetics, they are becoming more and more important in the pharmacy. We have always known that not all people react the same way to a medication. Certain medications work well for some people and not for others. Now we think some of this difference could be from genetics. Lets look at two blood thinners, warfarin and clopidogrel.

Warfarin is a very common blood thinner. It thins the blood by effecting how Vitamin K is used in the body. Vitamin K is involved in the clotting cascade which is a complex series of chemical steps that lead to blood clots. Two enzymes that effect how warfarin works are the one that breaks down warfarin in the liver and other that helps the body form Vitamin K. There are different genetic variations of these enzymes in different people. So, one 5 mg tablet of warfarin may thin the blood a lot in one person and not very much in another depending on the genetic variations of these enzymes.

There was a study was to see if genetic testing could help doctors to better choose doses of warfarin for their patients. They did genetic testing of 868 patients on warfarin and compared them to 2688 controls on warfarin without genetic testing. The result was that the people with the genetic testing had less side effects than the non tested patients. So we should do the warfarin genetic tests on everyone, right? Well, not yet. The problem is that the genetic testing is very expensive. And, there are those that argue that the people in the genetic testing arm of the study were just followed more closely than the control group and that is why they did better. So at the moment doing the standard INR test is still the most cost effective way to adjust someones warfarin dose. Down the road, will we be doing genetic tests? Maybe.

Clopidogrel or plavix is a different blood thinner. Clopidogrel is a pro-drug. It must be broken down by an enzyme to be activated. Last November clopidogrel was in the news because the FDA in the US said the stomach medication omeprazole slowed down this activating enzyme and that might make clopidogrel a less effective blood thinner. Now, the FDA is requiring a warning on clopidogrel about the different genetic variations of the activating enzyme. About 3% of us are poor clopidogrel metabolizers, which means that if you give us clopidogrel our genetic variation of the enzyme wont activate it very well and our blood wont be thinned as much. There is a genetic test to see if you are a poor metabolizer of clopidogrel, but again it is expensive and not very common in Canada. And the studies havent been done to see if the results of the genetic tests would help patients or not. So this is another example of a genetic test that might be helpful down the road , but not today.

So whether you are the great great great grandchild of the father of evolutionary biology or you are on a blood thinner, genetics may play a pivotal role in your health

As always if you have any questions or concerns about these or other products, ask your pharmacist.

 


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