Pharmacogenetics of Warfarin Induction and Inhibition

The research question is: How does CYP2C9 genotype modify warfarin drug interactions?

People differ in their genetic makeup. This includes differences in genes involved in drug metabolism, transport, and effect in the body. People with certain genetic profiles produce altered enzymes, transporters, and receptors that may respond in different ways to drugs. Altered enzymes cause some drugs to be broken down at a different rate than normal. As a result, drug concentrations build up in the blood, and increase the risk of side effects. Furthermore, when two drugs are taken together, the possibility exists for the drugs to interact, with one drug causing a change in the metabolism of the other or both of the drugs. It is not known whether people with an altered genetic makeup also have an altered experience with drug interactions. Altered drug transporters can affect the absorption and elimination of drugs as compared to normal causing differences in how long the drug stays in the body. Finally, altered drug receptors can respond differently to drugs and, thus, produce altered desired or undesired effects.

In this study, the investigators will be investigating the drug interactions with the commonly used anticoagulant drug warfarin in subjects with five different CYP2C9 genotypes. The CYP2C9 genotype is particularly important because this drug metabolizing enzyme governs the metabolic clearance of the more potent chemical entity (the S-enantiomer) of the drug. Warfarin is used for the treatment and prevention of life-threatening abnormal blood clots such as deep vein thrombosis, myocardial infarction, and strokes. The investigators chose warfarin for this study because it is a commonly used drug and must be monitored closely to avoid side effects. The investigators are interested in studying whether individuals with certain genetic alleles of the CYP2C9 genotype react differently to warfarin when it is combined with an antifungal (fluconazole) that inhibits CYP2C9-mediated metabolism and an antibiotic (rifampin) that induces CYP2C9-mediated metabolism. This research is being done to see if certain genetic profiles require us to adjust warfarin doses differently than is needed for the general population.

The study hypothesis is: Functionally defective CYP2C9 alleles attenuate the warfarin-fluconazole inhibitory interaction and exacerbate the warfarin-rifampin inductive interaction.