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How genetic testing can prevent some medication errors

Published July 25, 2013

How many people do you know who were given medication to treat an illness, but wound up with side effects that were worse than their original complaint?

Every year in the United States, more than 2.4 million people suffer a serious adverse drug reaction; more than 100,000 die.

Sometimes an entirely inappropriate drug or dosage is given, with disastrous results. But sometimes, the trouble is that an individual's body metabolizes a medication in an unpredictable way that renders the drug useless at best, harmful at worst.

But what if physicians had a way of learning how their patients would react before they tried a new drug?

Pharmacogenomics is the science that examines small genetic variations in DNA to predict whether a patient will have a good response, a bad response or no response at all to a drug. This kind of genetic testing also can help determine the best dosage, rather than using the old trial-and-error method.

Just as genes contribute to whether you will be tall or short, they also help determine how you will respond to medication.

The labels of many FDA approved drugs — from antibiotics and statins to the antirejection medications used by organ recipients — now mention commercially available genetic tests.

Genotyping kits to evaluate the metabolism of multiple medications are approved by the FDA, and can be administered at commercial labs across the nation.

But the tests can be extremely expensive, ranging from $400 dollars to a couple of thousands, and aren't routinely covered by insurance. They shouldn't be used routinely, but they should be covered by insurance more often than they are now.

Testing is especially important before administering a drug that was developed based on pharmacogenomics. For instance, the drug Herceptin, widely used in some breast cancer patients, is only effective when tumor cells have accumulated extra copies of the HER-2 gene and have high levels of the protein this gene produces.

But I believe it also ought to be used for patients with certain chronic diseases that will require long term treatment.

In my field, rheumatology, a drug called Imuran is used to treat autoimmune conditions such as chronic autoimmune hepatitis, scleroderma, lupus, leukemia and even inflammatory bowel disease.

It is metabolized in the body, producing compounds that suppress an overactive immune response. But in people who are low in a particular enzyme, Imuran can cause rare but serious side effects, like suppressing bone marrow production, or even a potentially life-threatening skin reaction.

There's an FDA-approved test to reveal whether an HIV patient has a strain of the virus that is genetically resistant to some anti-retroviral drugs. In such cases, different medication can be used.

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Another test looks at liver enzymes that process antidepressant drugs, opening the way to finding safer and more effective medications without the trial-and-error period many patients go through.

Pre-testing patients who need long term blood-thinners may be a good idea to reduce rates of hospitalization due to bleeding or embolism. As many as 10 percent of chronic pain patients don't respond to codeine treatment, and they might find better finding relief through testing.

In the near future, pharmacogenetics testing will enable doctors to hit the goal of finding the right medication, at the right dose, the first time, every time. This will mean safer, more effective treatments. And it could keep drugs that are toxic to some available to those who can tolerate them, and for whom they may be lifesaving.

If you agree with my perspective, I encourage you to sign my petition to the surgeon general. Go to change.org, and type my name into the search box, and you'll find it.

Dr. Edgard Janer is a board-certified physician practicing rheumatology in the Tampa Bay area since 1996. He can be reached at edrheuma@aol.com.