When your doctor writes you a prescription, you may assume that it’s just a matter of matching the medication to the condition that’s being treated. Not so.
In reality, doctors are trained to narrow down the medication options—sometimes several of them—by taking into account such factors as your age, sex and weight. Until recently, that’s all doctors have had to go on.
Now: The medication-choosing process has become far more sophisticated. With pharmacogenomics, also known as drug-gene testing, your doctor can use your genetic profile (genotype) to determine in advance if a drug is likely to be effective…the best dose…and how likely you are to have side effects. This breakthrough is now available for many commonly used medications, including heartburn drugs, painkillers, antidepressants, statins and certain cancer drugs.
Here’s how to put drug-gene testing to work for you—or a loved one…
The genes that you inherited from your parents largely determined what you look like—and even, to an extent, how you act and feel. Are you tall or short? What’s your blood type? Are your eyes blue or brown?
Genes, the chemical sets of instructions that the body uses to build proteins, play an important role in making you you—and that includes how you respond to medications. In the future, it’s likely that every drug—including over-the-counter standbys such as aspirin—will take genetics into account.
Suppose that you have colon cancer and will need chemotherapy. Your oncologist will pick the drugs with the best record of success. For example, two of the most effective drugs for this cancer are cetuximab (Erbitux) and pan-itumumab (Vectibix). Yet research has shown that they’re not the best choice for about 40% of patients with a particular genetic profile.
Another example: Patients with cardiovascular disease are often given warfarin (Coumadin), a blood thinner. It’s very effective at preventing clots, but it has a high risk for side effects, such as excessive bleeding—particularly when the dose isn’t exactly right. For those with a particular genetic profile, the drug is up to three times more potent than in those with different genes. These patients should be given a much lower dose.
For now, genetic tests are available for more than 150 FDA-approved drugs. (For a complete list of FDA-approved drugs with pharmacogenomic information on the label, go to the FDA website.)
If your doctor plans to start you on one of these medications, ask him/her about going to a laboratory to give a blood/saliva sample. This can be used to create your unique genetic profile.
Important: A single test can’t predict how you’ll respond to all medications. You might need additional tests if you’re taking more than one drug—although some test “panels” will include information on multiple medications.
The cost of a drug-gene test can be as little as about $100. More specialized tests—for the drugs used to treat some cancers, for example—can be as high as $7,000. Check with your health insurer to make sure the cost of the test is covered.
Genetic variations could account for anywhere from 20% to 95% of the difference in individual responses to various medications, according to a recent review of studies that appeared in The New England Journal of Medicine.
Because there’s such a high probability that drug-gene testing may yield helpful information, it’s wise to discuss with your doctor whether genetic testing is available for any medication he may prescribe for you. The results could affect the prescribed dose…the likelihood of side effects…or even cause your doctor to choose a different drug. Examples…
• Statins. Depending on the drug, this class of medications can lower LDL “bad” cholesterol by up to 55%—in some people. In others, the results can be quite different. For example, one large study found that more than 13% of participants who took the statin pravastatin (Pravachol) failed to lower their LDL by even 10%.
Reason: Some genetic variations make people “poor responders” to statins. They might require a higher-than-normal dose…or a different drug altogether, such as a fibrate like gemfibrozil (Lopid). Other genetic variations cause people to metabolize statins too quickly, which increases the risk for muscle pain or other side effects.
• Proton pump inhibitors (PPIs). Drugs in this class, such as omeprazole (Prilosec) and lansoprazole (Prevacid), inhibit the production of stomach acid and are widely used to treat heartburn and stomach and duodenal ulcers. Researchers have identified a number of genetic variations that affect how well these medications work.
Patients who are “extensive metabolizers,” for example, will require a higher dose than those who have genetic factors that cause them to metabolize the drugs more slowly.
• Selective serotonin reuptake inhibitor (SSRI) antidepressants. SSRIs require a lot of trial and error. About half of patients with depression don’t improve on their first drug. Their success on second and third drugs is even lower.
With genetic tests, psychiatrists can make more than an educated guess about which drug and doses to try. An analysis of studies presented at a meeting of the International College of Neuropsychopharmacology found that genetics-based prescribing for SSRIs doubled response rates as well as the rate of remission.
• Painkillers. Codeine is among the most effective (and least expensive) analgesics, but some individuals have a genetic variation that inhibits their ability to convert it into morphine (the mechanism that provides its pain-relieving effect). They usually require a higher dose—or sometimes a different medication, such as fentanyl or hydromorphone.
Another genetic variation causes codeine to be metabolized much more rapidly than normal. These patients are more likely to suffer serious side effects, including impaired breathing, when they’re given a standard dose.
