Did you ever wonder why a certain medicine works perfectly for your friend but has no effect on you? Or why different doses work for different people?
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Well, part of the answer to that question is your DNA. DNA not only determines your eye color, hair color and how tall you are, but it also plays a role in how your body processes medications. We know this because of pharmacogenetics, the study of how people’s genetic makeup affects their response to drugs.
Pharmacogenetics is a key concept in personalized healthcare. In the not-too-distant future, doctors will be able to use pharmacogenetics to find the most effective medicine at the most effective dose. They already can, in some cases.
Dosing for warfarin (brand name Coumadin), which prevents blood clots and is used to treat several heart conditions, is a challenge. If the dose is too high, it can lead to excessive bleeding. If it’s too low, it can actually lead to blood clots — the very thing it’s supposed to prevent.
That’s where pharmacogenetic testing comes in. Though not widespread, there is a test to help doctors identify how each person will respond to warfarin. This means they can get the dose right much more quickly than with the standard trial-and-error method.
Screenings like this are becoming more common. For example, a test is available to determine how people will respond to SSRIs (selective serotonin reuptake inhibitors), drugs used to treat depression. Over time, we hope such tests will become more widespread — and more accessible to patients.
What does a “boxed warning” mean?
Currently, there are more than 100 FDA approved medications with pharmacogenetic information on their labels. Why labels? Because the FDA sometimes requires you and your doctor to take specific actions based on genetic information before you use a drug.
A small number of drugs on the list have this ‘boxed warning,’ the most serious level of warning issued by the FDA. The FDA reserves this warning for medications that may have serious — sometimes fatal — complications for people who carry a rare genetic marker. If tests show that you are a carrier, your physician will either alter the dose of your medication or prescribe an alternate treatment.
The current standard of care calls for pharmacogenetic testing when a physician prescribes any of the ‘boxed warning’ medications, and doctors may call for pharmacogenetic testing for some of the other drugs on the list. Your physician and pharmacist will know about this information, so be sure to ask.
The good news is that insurance should cover testing for any of the ‘boxed warning’ drugs, and possibly for others on the FDA’s list.