The US FDA has cleared for marketing the first laboratory test system that will allow physicians to consider unique genetic information from patients in selecting medications and doses of medications for a wide variety of common conditions such as cardiac disease, psychiatric disease, and cancer.

The new test is the AmpliChip Cytochrome P450 Genotyping Test made by Roche Molecular Systems, Inc., of Pleasanton, California. It was cleared for use with the Affymetrix GeneChip Microarray Instrumentation System, manufactured by Affymetrix, Inc., of Santa Clara, California.

The new test is the first DNA microarray test to be cleared by the FDA and its clearance paves the way for similar microarray-based diagnostic tests to be developed in the future. A microarray is similar to a computer microchip, but instead of tiny circuits, the chip contains millions of tiny DNA molecules. The test is performed using DNA that is extracted from a patient's blood. A person's DNA sequence is determined based on the sequence of the probe molecule to which the DNA is most similar.

"Physicians can use the genetic information from this test to prevent harmful drug interactions and to assure drugs are used optimally, which in some cases will enable patients to avoid less effective or potentially harmful treatment choices," said Dr. Lester M. Crawford, Acting FDA Commissioner.

The new test analyzes one of the genes from a family of genes called cytochrome P450 genes, which are active in the liver to break down certain drugs and other compounds. Variations in this gene can cause a patient to metabolize certain drugs more quickly or more slowly than average, or, in some cases, not at all. The specific enzyme from this family that is analyzed by this test, called cytochrome P4502D6, plays an important role in the body's ability to metabolize some commonly prescribed drugs including antidepressants, anti-psychotics, beta-blockers, and some chemotherapy drugs.

The test is not intended to be a stand-alone tool to determine optimum drug dosage, but should be used along with clinical evaluation and other tools to determine the best treatment options for patients, FDA said in its release.

FDA cleared the test and the scanner based on results of a study conducted by the manufacturers of hundreds of DNA samples as well as on a broad range of supporting peer-reviewed literature.