An Overview of Pharmacogenomics

What It Is and How It’s Used in Medicine

Pharmacogenomics is a new field of medicine that focuses on how a person’s genetic makeup responds to certain drugs. It combines two studies of medicine: pharmacology (the science of drugs) and genomics (the study of genes). When these two areas of medicine are combined, the ideal result is a personalized medication roadmap that takes into account a person’s genes and how well they respond to specific treatments and medications.

This is a topic that is being widely discussed and researched in many fields, from medicine to personalized nutrition, in an effort to manage and prevent diseases.

Benefits of Pharmacogenomics
Illustration by Brianna Gilmartin, Verywell​

How Genes Affect Medication

Past research has discovered that certain proteins can affect how drugs work within the body. This is because proteins in the body are responsible for breaking down and absorbing medications. The chemicals in medications also attach themselves to proteins, affecting potency and how well the medication works once it's in your system.

Your genes are segments of deoxyribonucleic acid (DNA), which is the complete molecule that makes up how our bodies function, the color of our hair and eyes, as well as provides instructions that are used in growth, body functioning, and building protein molecules. By looking at the variation of genes in the proteins that DNA produces in a person, researchers are able to tell if certain proteins result in chemical changes which would make drugs less effective, less safe, or cause side effects.

Since each person has different side effects to certain medications based on their genes, one of the biggest revelations in genomics is that there is no universal result when prescribing a drug to a patient. 

By implementing pharmacogenomics into routine practice, health care providers will be able to use the information about your genes to prescribe you the medicine that will have the greatest chance of helping you with the least amount of adverse effects or risks.

This accuracy in prescribing the best medication that works for you individually would also save you money—you would not have to try out several different medications before finding the one that works. Among its other uses and benefits, the goal of pharmacogenomics is to take the guesswork out of prescribing treatment to patients.

Pharmacogenomics Testing

Pharmacogenomic testing is a simple procedure to determine if a medication is right for you. Testing can also reveal whether a certain dosage is correct or if you will have serious side effects from a medication before you start regularly taking it. Testing is usually done by taking a small blood or saliva sample. You will need a separate pharmacogenomics test for each medication that is under review.

However, since your genetic makeup does not change, you won’t need to be retested in your response to a certain medication after getting your results the first time. While each person has a unique set of DNA, family members can share certain genes—this means your health care provider may be able to recommend that certain family members get tested to determine how they will respond to specific medications if you have a shared history of certain conditions.

Limitations

Since pharmacogenomic testing is a new field of medicine, testing will not always provide an accurate result for a patient. Since each medication requires its own test, your health care provider will need to sign off on each specific test in correlation to all of the medications you are taking. Even so, testing is not available for all medications.

Ultimately, there may not be a way to know how a medication will affect you before taking it aside from trial and error.

Pharmacogenomics is also not available for over-the-counter medications, like aspirin and other pain relievers. The Food and Drug Administration (FDA) is considering genetic testing for certain blood-thinners (like Coumadin and Plavix) to determine if the information would be helpful when determining the proper dosage for certain patients.

Depending on your insurance plan and coverage, pharmacogenomic testing may not be covered. This could be quite costly, especially if you need more than one test to cover the medications you’re taking. The price of testing ranges from $250 to $500. If the FDA requires testing before taking a certain medication, most insurance plans will reimburse you for the testing fee.

For testing not required by the FDA but advised by your health care provider, your insurance may not cover all of the fee or any of it. Drugs costs as a whole may also temporarily spike due to the results of pharmacogenomic testing, as new drugs are put on the market and drug companies aim to regain their development costs.

Pharmacogenomics and Cancer Treatments

Pharmacogenomics is being most widely used in the prescription of cancer drugs and chemotherapy treatments. This is an important area for pharmacogenomics because, in the instance of cancer, there are two sets of genes (called genomes) that impact drug prescription and treatment: the genome of the patient and the genome of the cancerous tumor. For example, in women with breast cancer, the drug trastuzumab (known as Herceptin) only works for women with tumors that have a genetic profile which leads to an overproduction of a specific protein called HER2.

In patients with acute lymphoblastic leukemia (ALL), a cancer of the blood and bone marrow that affects white blood cells, the chemotherapy drug mercaptopurine (Purinethol) can affect some patients' abilities to process and absorb the drug based on their genes. Health care providers need to specifically alter the dose based on an individual's genetic makeup to prevent the increased risk of infection and other severe side effects.

Another instance relating to cancer occurs with patients undergoing treatment for colon cancer. The chemotherapy drug irinotecan (Camptosar) may give some patients diarrhea and increased risk of infection due to the fact that their genetic makeup makes it difficult for their bodies to metabolize the drug. In turn, their bodies can't get rid of the drug from their system quickly enough.

In this case, health care providers would perform a pharmacogenomic test called UGT1A1 on a patient to see if she or he had this genetic variation. If so, they would need to make sure this patient is getting lower amounts of the drug administered (which is typically just as effective as the higher dosage for these patients).

Pharmacogenomics and Other Illnesses

Pharmacogenomics is helpful in illnesses other than cancer, such as autoimmune diseases like Crohn’s disease and rheumatoid arthritis. A common pharmacogenomic test for these conditions is thiopurine methyltransferase testing (TPMT) for patients who may be a match for thiopurine drug therapy.

TPMT enzymes help to break down thiopurine drugs. However, if a person is deficient in these enzymes, the high concentration of the drug in this person’s system can have serious side effects including damage to their bone marrow. If there is a TPMT deficiency, the patient would need a lower dose or alternate drug as part of their treatment plan.

In certain mental health disorders, pharmacogenomics may be able to help identify which drugs a person would respond to and how quickly.

In the case of depression, many patients don’t respond to the first drug prescribed. Since each medication can take weeks to completely take effect, getting the proper medication is crucial. Researchers have discovered that certain genetic compositions can affect the response to the drug citalopram (Celexa), a selective serotonin reuptake inhibitor (SSRI), and a popular antidepressant used for depression. Pharmacogenomics can help identify how patients will respond to SSRIs which will affect their treatment and overall outcome.

Pharmacogenomics and Older Drugs

Certain drugs never make it past the development phase, but with pharmacogenomics, they may be able to complete development and be put into use for patients that are a genetic fit—some drugs might even be useful in ways health care providers did not foresee.

One example of this is the beta-blocker drug bucindolol (Gencaro), which was halted from production after two other similar drugs were approved by the FDA. Researchers discovered that the drug is helpful for those with certain genes that regulate heart function. If approved by the FDA, the drug would be one of the first heart drugs where pharmacogenomic testing is required before prescribing.

The Future of Pharmacogenomics

In the past, doctors prescribed medications based on a patient’s age, weight, sex, and organ (specifically the kidney and liver) function. Pharmacogenomics is a new field of medicine that will help doctors take into account detailed specifications about each patient, resulting in more accurate treatment plans and fewer side effects for patients. The FDA currently has pharmacogenomic information on the labels of 200 medications for various diseases ranging from cancer to gastrointestinal issues to infectious diseases.

With continued research and development, the number of diseases for which pharmacogenomics can develop treatment plans is expected to grow, in addition to the diseases it has already begun developing treatments for including Alzheimer’s diseaseheart disease, HIV/AIDS, asthma, and more.

A Word From Verywell

Pharmacogenomics is a new field of medicine that focuses on using information about a person's genes in order to foresee how a person will react to medication prior to him or her taking it. This would provide a host of benefits, including saving the patient from unnecessary side effects of medications as well as saving money on medications that are not effective. Pharmacogenomics applies to diseases ranging from cancer and gastrointestinal conditions to mental health issues such as depression, which can benefit many people.

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