Medications Genetics Pt II

We previously shared the case of a patient, Debbie, who had hEDS and medication intolerance, leading to a pharmacogenomics (PGx) consultation. In this post, we’ll explore more reasons why a PGx referral may be needed, and how it can help.

 Why is pharmacogenomics important?

People react differently to drugs, partly due to their genetics. Maybe you or someone you know has taken a correctly prescribed medication that was not a good fit. This can cause unwanted outcomes, such as:

• Severe or intolerable side effects. Side effects can be so severe leading someone to stop taking the drug. Women are at especially increased risk due to biological differences that impact how a drug is metabolized, distributed, and eliminated. This can make women more susceptible to increased levels of drugs which is linked to more side effects. It is never a good day when a patient tells me that side effects are worse than their disease symptoms!
• Drugs don't work as well. Some people may report limited benefits from their medications, like Debbie with her tramadol.
• Did you know that adverse drug events are the fourth leading cause of death in the U.S.? Studies estimate that over 100,000 patients die every year from serious adverse drug reactions, making them the fourth leading cause of death in the US.

PGx can reduce the risk of bad reactions by helping us predict how a person will respond to a drug even before they take it. Examples include:

• Testing HLA genes can identify if you are at risk of drug hypersensitivity reactions to medications such as the HIV drug abacavir (Ziagen) and the antiseizure medications carbamazepine (Carbatrol) and phenytoin (Dilantin).
• Testing the CYP2D6 gene can predict whether the pain relievers tramadol (Cozip, Qdolo) and codeine and the breast cancer drug tamoxifen (Soltamox) will work for you or produce intolerable side effects.
• Testing the CYP2C19 gene can predict whether the antidepressant citalopram (Celexa), the blood thinning medication clopidogrel (Plavix) and the acid-reducing medication omeprazole (Prilosec) will work for you or produce intolerable side effects.

What should l know about pharmacogenomics testing?

Most testing requires either a cheek swab or a blood draw. If you elect cheek swab testing, be sure to avoid putting anything in your mouth, including tobacco, smoking, chewing gum, liquids, foods, and medications for at least 30 minutes prior to the swab. If you're giving a blood sample, these rules do not apply.

Once the results are back, you may meet with a pharmacist, or a physician trained in pharmacogenomics to help interpret the results in the context of your medications or conditions.

Insurance companies have gotten better about covering the cost of PGx, but I advise you still check with your insurance prior to testing. Some people will hesitate to get PGx testing for fear of being discriminated against by their health insurance company or employer. The Genetic Information Nondiscrimination Act, passed in 2008, prevents such discrimination. However, it does not apply to military insurance or to life, long-term care, or disability insurance.

What about Debbie? How can it help her?

Her PGx testing revealed her to be a CYP2D6 poor metabolizer, which meant she could not properly metabolize common drugs such as antidepressant paroxetine (Paxil), increasing her risk of side effects. In addition, it also showed that tramadol was likely to not work for pain. Considering her experience with these medications, Debbie felt validated.

However, PGx testing could not account for lack of efficacy with lidocaine. Efforts are ongoing to help us understand why many of patients with hEDS have similar experience. Advances in genomics medicine and technology will bring us closer to understanding.

To learn more about pharmacogenomics testing visit: https://www.cdc.gov/genomics/disease/pharma.htm.

Do you have experience with adverse reaction to medications? Share in the comments below.

Author: Adrijana Kekic, Pharm.D., BCACP