Genetic tool gives insight into patient drug reactions

Test eventually could give information at birth

Genetic testing to identify possible drug interactions is becoming more commonplace across the country. The emerging technology is here, and such tests eventually may be given at birth, says John Lima, PharmD, director of the Nemours Center for Clinical Pediatric Pharmacology in Jacksonville, FL.

Companies are already testing drug-metabolizing enzymes that have been shown to affect how the body handles a drug. "I think the drug-metabolizing enzymes are the first ones that have been discovered. There are labs that are doing this in the country right now. There is one such test that I believe might even be paid by a third party," he says.

But other proteins in the body that are encoded by highly polymorphic genes can influence response to drugs, Lima says. "I believe that certainly within 10 years, we will be doing that not only for drug-metabolizing enzymes but other proteins."

One company that offers genetic testing to see how a particular patient’s genetic makeup affects drug metabolism is Seryx in Montreal. The technology, called Signature Genetics, is used primarily at physician offices across the country, although some health systems such as Baylor in Texas have recently signed on. Seryx CEO Fred Mannausau notes that more health systems will soon follow.

The offices sign a contract with the testing company, and the technology is made available to the physicians’ patients. A patient can then visit the physician’s office and have his or her blood drawn and a cheek swab analysis. The samples are sent to Montreal, where DNA material is extracted. The DNA material then is sent for analysis to a lab in Germany. About a month later, a report that covers how 150 of the most common medicine types are metabolized based on the patient’s genetic makeup is sent to the physician.

The test can be costly, about $2,000. However, it particularly benefits two types of patients, Mannausau says. One is the patient who has a history of side effects with drugs. "There is a higher possibility that it could be caused by a genetic component."

The other one is a patient who takes several drugs and doesn’t seem to be getting any benefit. "That could mean that they are metabolizing the drug so rapidly that they need a much higher dosage to get to the right level in their blood," he says.

Codeine is one example of a drug that a patient may have trouble metabolizing, Lima says. "By itself, it doesn’t have any activity and has to be converted in the liver to morphine, which is the active ingredient."

Patients who don’t have the enzyme that converts codeine to morphine will have no response to codeine. "You would want to know that beforehand," he says. "A lot of people believe codeine is safer and is more heavily prescribed. But the patients who can’t convert it would have to have morphine or some other drug. If you knew that before, you could save the patient a lot of pain, discomfort, and cost."

Patients using the Signature Genetics tech-nology can continue to be in the system for an annual membership fee of about $250. If new drugs are approved, the service will inform the patient. Also, if a patient changes a drug and is taking other drugs, the patient will get an updated report on the new drug interactions, as well. The updates are automatic and are sent one or two times a year.

Pharmacy has a huge role to play in this business, Lima says. "Particularly early on, clinical pharmacists may have more knowledge about these polymorphisms and their influence so that physicians may want to seek out their advice."

The tests will be cost-effective the more they are done on a broad basis, he reports. "We will be seeing more of them."