New Gene Tests Can Predict if a Drug Will Work for a Patient

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What if there were tests that could tell you whether the following drugs were a good match for your patients: Antidepressants, statins, painkillers, anticlotting medicines, chemotherapy agents, HIV treatments, organ transplant antirejection drugs, proton pump inhibitors for heartburn, and more?

That’s quite a list. And that’s pharmacogenetics, testing patients for genetic differences that affect how well a given drug will work for them and what kind of side effects to expect.

“About 9 out of 10 people will have a genetic difference in their DNA that can impact how they respond to common medications,” said Emily J. Cicali, PharmD, a clinical associate at the University of Florida College of Pharmacy, Gainesville, Florida.

Cicali is the clinical director of UF Health’s MyRx, a virtual program that gives Florida and New Jersey residents access to pharmacogenetic (PGx) tests plus expert interpretation by the health system’s pharmacists. Genetic factors are thought to contribute to about 25% or more of inappropriate drug responses or adverse events, said Kristin Wiisanen, PharmD, dean of the College of Pharmacy at Rosalind Franklin University of Medicine and Science in North Chicago, Illinois.

“Pharmacogenetics helps consumers avoid drugs that may not work well for them or could cause serious adverse events. It’s personalized medicine,” Cicali said.

Through a cheek swab or blood sample, the MyRx program — and a growing number of health system programs, doctors’ offices, and home tests available across the United States — gives consumers a window on inherited gene variants that can affect how their body activates, metabolizes, and clears away medications from a long list of widely used drugs.

Why PGx Tests Can Have a Big Impact

These tests work by looking for genes that control drug metabolism.

“You have several different drug-metabolizing enzymes in your liver,” Cicali explained. “Pharmacogenetic tests look for gene variants that encode for these enzymes. If you’re an ultrarapid metabolizer, you have more of the enzymes that metabolize certain drugs, and there could be a risk the drug won’t work well because it doesn’t stay in the body long enough. On the other end of the spectrum, poor metabolizers have low levels of enzymes that affect certain drugs, so the drugs hang around longer and cause side effects.”

While pharmacogenetics is still considered an emerging science, it’s becoming more mainstream as test prices drop, insurance coverage expands, and an explosion of new research boosts understanding of gene-drug interactions, Wiisanen said.

Politicians are trying to extend its reach, too. The Right Drug Dose Now Act of 2024, introduced in Congress in late March, aims to accelerate the use of PGx by boosting public awareness and by inserting PGx test results into consumers’ electronic health records. (Though a similar bill died in a US House subcommittee in 2023.)

“The use of pharmacogenetic data to guide prescribing is growing rapidly,” Wiisanen said. “It’s becoming a routine part of drug therapy for many medications.”

photo of PGx test

What the Research Shows

When researchers sequenced the DNA of more than 10,000 Mayo Clinic patients, they made a discovery that might surprise many Americans: Gene variants that affect the effectiveness and safety of widely used drugs are not rare glitches. More than 99% of study participants had at least one. And 79% had three or more.

The Mayo-Baylor RIGHT 10K Study — one of the largest PGx studies ever conducted in the United States — looked at 77 gene variants, most involved with drug metabolism in the liver. Researchers focused closely on 13 with extensively studied, gene-based prescribing recommendations for 21 drugs including antidepressants, statins, pain killers, anticlotting medications for heart conditions, HIV treatments, chemotherapy agents, and antirejection drugs for organ transplants.

When researchers added participants’ genetic data to their electronic health records, they also sent semi-urgent alerts, which are alerts with the potential for severe harm, to the clinicians of 61 study volunteers. Over half changed patients’ drugs or doses.

The changes made a difference. One participant taking the pain drug tramadol turned out to be a poor metabolizer and was having dizzy spells because blood levels of the drug stayed high for long periods. Stopping tramadol stopped the dizziness. A participant taking escitalopram plus bupropion for major depression found out that the combo was likely ineffective because they metabolized escitalopram rapidly. A switch to a higher dose of bupropion alone put their depression into full remission.

“So many factors play into how you respond to medications,” said Mayo Clinic pharmacogenomics pharmacist Jessica Wright, PharmD, BCACP, one of the study authors. “Genetics is one of those pieces. Pharmacogenetic testing can reveal things that clinicians may not have been aware of or could help explain a patient’s exaggerated side effect.”

Pharmacogenetics is also called pharmacogenomics. The terms are often used interchangeably, even among PGx pharmacists, though the first refers to how individual genes influence drug response and the second to the effects of multiple genes, said Kelly Caudle, PharmD, PhD, an associate member of the Department of Pharmacy and Pharmaceutical Sciences at St. Jude Children’s Research Hospital in Memphis, Tennessee. Caudle is also co-principal investigator and director of the National Institutes of Health (NIH)-funded Clinical Pharmacogenetics Implementation Consortium (CPIC). The group creates, publishes, and posts evidence-based clinical practice guidelines for drugs with well-researched PGx influences.

By any name, PGx may help explain, predict, and sidestep unpredictable responses to a variety of drugs:

  • In a 2023 multicenter study of 6944 people from seven European countries in The Lancet, those given customized drug treatments based on a 12-gene PGx panel had 30% fewer side effects than those who didn’t get this personalized prescribing. People in the study were being treated for cancer, heart disease, and mental health issues, among other conditions.
  • In a 2023 study from China’s Tongji University, Shanghai, China, of 650 survivors of strokes and transient ischemic attacks, those whose antiplatelet drugs (such as clopidogrel) were customized based on PGx testing had a lower risk for stroke and other vascular events in the next 90 days. The study was published in Frontiers in Pharmacology.
  • In a University of Pennsylvania study of 1944 adults with major depression, published in the Journal of the American Medical Association, those whose antidepressants were guided by PGx test results were 28% more likely to go into remission during the first 24 weeks of treatment than those in a control group. But by 24 weeks, equal numbers were in remission. A 2023 Chinese meta-analysis of 11 depression studies, published in BMC Psychiatry, came to a similar conclusion: PGx-guided antidepressant prescriptions may help people feel better quicker, perhaps by avoiding some of the usual trial-and-error of different depression drugs.

PGx checks are already strongly recommended or considered routine before some medications are prescribed. These include abacavir (Ziagen), an antiviral treatment for HIV that can have severe side effects in people with one gene variant.

The US Food and Drug Administration (FDA) recommends genetic testing for people with colon cancer before starting the drug irinotecan (Camptosar), which can cause severe diarrhea and raise infection risk in people with a gene variant that slows the drug’s elimination from the body.

Genetic testing is also recommended by the FDA for people with acute lymphoblastic leukemia before receiving the chemotherapy drug mercaptopurine (Purinethol) because a gene variant that affects drug processing can trigger serious side effects and raise the risk for infection at standard dosages.

“One of the key benefits of pharmacogenomic testing is in preventing adverse drug reactions,” Wiisanen said. “Testing of the thiopurine methyltransferase enzyme to guide dosing with 6-mercaptopurine or azathioprine can help prevent myelosuppression, a serious adverse drug reaction caused by lower production of blood cells in bone marrow.”

When, Why, and How to Test

“A family doctor should consider a PGx test if a patient is planning on taking a medication for which there is a CPIC guideline with a dosing recommendation,” said Teri Klein, PhD, professor of biomedical data science at Stanford University, Stanford, California, and principal investigator at PharmGKB, an online resource funded by the NIH that provides information for healthcare practitioners, researchers, and consumers about PGx. Affiliated with CPIC, it’s based at Stanford University.

You might also consider it for patients already on a drug who are “not responding or experiencing side effects,” Caudle said.

Here’s how four PGx experts suggest consumers and physicians approach this option.

Find a Test

More than a dozen PGx tests are on the market — some only a provider can order, others a consumer can order after a review by their provider or by a provider from the testing company. Some of the tests (using saliva) may be administered at home, while blood tests are done in a doctor’s office or laboratory. Companies that offer the tests include ARUP Laboratories, Genomind, Labcorp, Mayo Clinic Laboratories, Myriad Neuroscience, Precision Sciences Inc., Tempus, and OneOme, but there are many others online. (Keep in mind that many laboratories offer “lab-developed tests” — created for use in a single laboratory — but these can be harder to verify. “The FDA regulates pharmacogenomic testing in laboratories,” Wiisanen said, “but many of the regulatory parameters are still being defined.”)

Because PGx is so new, there is no official list of recommended tests. So you’ll have to do a little homework. You can check that the laboratory is accredited by searching for it in the NIH Genetic Testing Laboratory Registry database. Beyond that, you’ll have to consult other evidence-based resources to confirm that the drug you’re interested in has research-backed data about specific gene variants (alleles) that affect metabolism as well as research-based clinical guidelines for using PGx results to make prescribing decisions.

The CPIC’s guidelines include dosing and alternate drug recommendations for more than 100 antidepressants, chemotherapy drugs, the antiplatelet and anticlotting drugs clopidogrel and warfarin, local anesthetics, antivirals and antibacterials, pain killers and anti-inflammatory drugs, and some cholesterol-lowering statins such as lovastatin and fluvastatin.

For help figuring out if a test looks for the right gene variants, Caudle and Wright recommended checking with the Association for Molecular Pathology’s website. The group published a brief list of best practices for pharmacogenomic testing in 2019. And it keeps a list of gene variants (alleles) that should be included in tests. Clinical guidelines from the CPIC and other groups, available on PharmGKB’s website, also list gene variants that affect the metabolism of the drug.

Consider Cost

The price tag for a test is typically several hundred dollars — but it can run as high as $1000-$2500. And health insurance doesn’t always pick up the tab.

In a 2023 University of Florida study of more than 1000 insurance claims for PGx testing, the number reimbursed varied from 72% for a pain diagnosis to 52% for cardiology to 46% for psychiatry.

Medicare covers some PGx testing when a consumer and their providers meet certain criteria, including whether a drug being considered has a significant gene-drug interaction. California’s Medi-Cal health insurance program covers PGx as do Medicaid programs in some states, including Arkansas and Rhode Island. You can find state-by-state coverage information on the Genetics Policy Hub’s website.

Understand the Results

As more insurers cover PGx, Klein and Wiisanen say the field will grow and more providers will use it to inform prescribing. But some health systems aren’t waiting.

In addition to UF Health’s MyRx, PGx is part of personalized medicine programs at the University of Pennsylvania in Philadelphia, Endeavor Health in Chicago, the Mayo Clinic, the University of California, San Francisco, Sanford Health in Sioux Falls, South Dakota, and St. Jude Children’s Research Hospital in Memphis, Tennessee.

Beyond testing, they offer a very useful service: A consult with a pharmacogenetics pharmacist to review the results and explain what they mean for a consumer’s current and future medications.

Physicians and curious consumers can also consult CPIC’s guidelines, which give recommendations about how to interpret the results of a PGx test, said Klein, a co-principal investigator at CPIC. CPIC has a grading system for both the evidence that supports the recommendation (high, moderate, or weak) and the recommendation itself (strong, moderate, or optional).

Currently, labeling for 456 prescription drugs sold in the United States includes some type of PGx information, according to the FDA’s Table of Pharmacogenomic Biomarkers in Drug Labeling and an annotated guide from PharmGKB.

Just 108 drug labels currently tell doctors and patients what to do with the information — such as requiring or suggesting testing or offering prescribing recommendations, according to PharmGKB. In contrast, PharmGKB’s online resources include evidence-based clinical guidelines for 201 drugs from CPIC and from professional PGx societies in the Netherlands, Canada, France, and elsewhere.

Consumers and physicians can also look for a pharmacist with pharmacogenetics training in their area or through a nearby medical center to learn more, Wright suggested. And while consumers can test without working with their own physician, the experts advise against it. Don’t stop or change the dose of medications you already take on your own, they say . And do work with your primary care practitioner or specialist to get tested and understand how the results fit into the bigger picture of how your body responds to your medications.

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