When Drugs Don't Work

Without the liver, most drugs would go through our bodies with little effect. The liver is able to metabolize, or break down, drugs and chemically alter them so that they become active, travel the bloodstream, and can eventually be excreted by the body.

But people with certain genetic variations lack the ability to metabolize some drugs, and could face life threatening complications if they're depending on the very drug their livers can't process.

The problem comes up in patients who get cardiac stents. It's a metal mesh tube that's inserted into a blocked artery to keep it open. A drawback is that, within months, scar tissue can re-block the artery.

In 2008, a new stent came out that slowly releases medication to prevent tissue growth. Yet the enormously popular stent carries a big risk: clot formation. The body responds to the bare metal as a foreign object and covers it with platelets, increasing the risk of a fatal heart attack or stroke.

Doctors prescribe blood thinners to help lower the risk; however a rather large percentage of people carry a genetic variation that does not metabolize the most commonly prescribed blood thinner, Plavix, which means the drug is rendered ineffective. Fifty percent of those of Asian descent, 30 percent of African, and 25 percent of European ancestry can carry this genetic variation.

Now, a company, Spartan Biosciences, has developed a bedside testing machine capable of detecting this gene. The gene encodes a liver enzyme belonging to a family of enzymes called P450 that is important in processing drugs. Of the eight known variants of this gene, seven encode inactive versions of the enzyme. The new machine can screen patients for this variant in about an hour. Spartan Biosciences is waiting regulatory approval and hopes to have it in hospitals by the end of the year.