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.
Dr. 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.
Dr. 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,” Dr. 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, Dr. 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,” Dr. Wiisanen said. “It’s becoming a routine part of drug therapy for many medications.”
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 E. Caudle, PharmD, PhD, an associate member of the Department of Pharmacy and Pharmaceutical Sciences at St. Jude Children’s Research Hospital in Memphis, Tennessee. Dr. 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 from China’s Tongji University, Shanghai, 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 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 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.