Pharmacogenomics

Not all medicines are affected by genetic differences. Your provider may order pharmacogenomic testing before you start a certain medicine, or if you're already taking a medicine that's not working and/or causing serious side effects.  

Here are a few common examples of when pharmacogenomic testing may be recommended.

Pharmacogenomics to determine the response to medicines

Clopidogrel

• Clopidogrel is used to prevent blood clots, for example after a stroke or a heart attack.
• When you take clopidogrel, it must be activated in your liver via the CYP2C19 enzyme before it can work.
• This doesn't work as well as expected for some people because of genetic differences (even if they have a healthy liver).
• These people will be at higher risk of another stroke or heart attack.
• Pharmacogenomic testing can tell you if you have a genetic difference in CYP2C19 which makes you less able to activate clopidogrel. You might need a higher dose of clopidogrel or another medicine to prevent blood clots.

Codeine

• Codeine is used for pain relief.
• Codeine works by being broken down in your liver via the CYP2D6 enzyme to morphine.
• People may respond differently to codeine depending on how their liver breaks down codeine. Some people may only need a very small dose of codeine for pain relief and be more likely to get side effects (such as constipation), while others may find that codeine doesn’t work well for them at all, and need a different pain medicine.

Pharmacogenomics to determine the risk of side effects

5-Fluorouracil (5-FU) and capecitabine

• 5-Fluorouracil (5-FU) and capecitabine are chemotherapy medicines used in the treatment of some cancers.
• They are processed in the body by an enzyme made in the liver, known as DPD (dihydropyrimidine dehyrogenase).
• If you have no DPD enzyme you can get serious side effects from 5-FU and capecitabine which may be life threatening. This is because your body is unable to process these medicines and they build up quickly, causing serious side effects.
• Pharmacogenomic testing for the DPYD gene which encodes for this enzyme is offered before treatment so you know, before you start these medicines, if you're at risk of serious side effects. If so, you can be offered a lower dose or a different medicine.

Statins such as atorvastatin and rosuvastatin

• Statins such as atorvastatin and rosuvastatin are medicines used to lower the level of cholesterol in your blood and protect your arteries.
• They help to reduce your chance of having a heart attack or stroke, or developing coronary artery disease.
• While most people can safely take statins, a few people can get side effects like muscle weakness or pain (myopathy) or, in rare cases, wasting of muscle (rhabdomyolysis).
• These reactions are often because of a genetic difference.
• Pharmacogenomic test results may help to guide your prescriber when recommending a medicine for cholesterol lowering.

A sample of your blood, saliva or cells from the inside of your cheek can be used for pharmacogenomic testing. The type of sample needed will depend on the laboratory (lab) where the sample is sent.

• Only some laboratories in Aotearoa New Zealand are able to do pharmacogenomic testing.
• Sometimes samples need to be sent to a lab outside Aotearoa New Zealand, usually Australia.
• You will be clearly informed if your sample needs to be sent outside Aotearoa New Zealand.

It’s important to know that in Aotearoa New Zealand, your genetic information is protected under the Privacy Act and can only be shared with healthcare providers directly involved in your care.