Interpreting Pharmacogenomic Tests
Pharmacogenomic test results can be difficult to interpret. There are limitations to interpretation because enzymes involved in drug metabolism arise from multiple genes and that process is often complex. The test results are predictions based on information about the specific genetic variations and on information about the associated diseases, adverse drug reactions, and patient outcomes that have been gathered during studies and clinical trials. In many cases, the predictions will be very accurate, but they cannot say with 100% certainty what will happen with an individual patient and they do not incorporate or make allowances for the other factors in a patient's life related to the disease condition or to the individual that may also affect their response to treatment. This is one of the reasons why the results are intended to be used in conjunction with other relevant clinical findings.
Some currently available pharmacogenomic tests include:
A DNA microarray that tests for 29 CYP2D6 genetic variants and 2 for the CYP2C19. It is meant to be used as an aid in individualizing treatment selection and dosing for drugs metabolized through these genes. It helps predict poor, intermediate, extensive, or ultra-rapid metabolizers. A test that detects variations in the UGT1A1 gene, which produces the enzyme UDP-glucuronosyltransferase. The enzyme is active in the metabolism of drugs such as irinotecan, a drug used in metastatic colorectal cancer treatment. The test is used to identify patients who may be at increased risk of adverse reaction to the drug. The gene that the test detects has been shown to be an effective genetic marker for predicting irinotecan-induced toxicity. Tests that detect genetic variants of the CYP2C9 and VKORC1 (vitamin K epoxide reductase) enzymes. These enzymes are involved in the efficacy of warfarin as an anticoagulant. Warfarin is used to prevent dangerous blood clots from forming in the blood vessels of certain patients, but it can significantly increase the risk of bleeding into the head or gastrointestinal tract. These tests identify patients who have genetic variations and so need a reduced dose of warfarin to avoid bleeding episodes. An FDA advisory committee voted in November 2005 in favor of changing Warfarin's label to reflect the fact that pharmacogenomic information can be useful in deciding a patient's individual dose. 
