Molecular diagnostic testing can help determine drug effectiveness or potential complications of drug therapy. There can be impaired drug metabolism that may lead to adverse drug reactions. There may be lack of drug response from increased drug metabolism.
One example is detection of HER2 amplification in breast cancers. The presence or absence of HER2 determines whether usage of trastuzumab, a monoclonal antibody directed at cancer cell surface growth factor receptor, will be effective. HER2, combined with detection of estrogen receptors (ER) and progesterone receptors (PR) in breast cancer cell nuclei, provides information about chemotherapy protocols and prognosis.
Cytochrome P450 mutations (polymorphisms) may predict how drugs act in specific individuals. One common polymorphism is the cytochrome p450 2C19 (CYP2C19) mutation that reduces metabolism of many drugs, including coumadin, clodiprogrel, omeprazole, and antidepressants such as amitriptyline). Coumadin anticoagulant effect is moderated by cytochrome P450 metabolism in hepatocytes. Decreased cytochrome P450 activity in some polymorphisms means that lower dosages of coumadin must be given.
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