Cytochrome P450 2C9 (CYP2C9) is a drug-metabolizing enzyme involved in the metabolism of several clinically important drugs, including warfarin, phenytoin, siponimod and some nonsteroidal anti-inflammatories. Individuals with some variant CYP2C9 alleles may experience a reduced therapeutic response and may be at risk for side effects from drugs that are metabolized by CYP2C9. CYP2C9 genotype information can be utilized to predict CYP2C9 metabolic phenotype, which can be used as an aid in determining a therapeutic strategy for drugs that are metabolized by CYP2C9. For example, CYP2C9 poor metabolizers mat experience increased concentrations of a drug with a reduced or absent therapeutic response. Warfarin metabolism is reduced by 30-50% by *2 and 90% by *3 alleles: individuals with at least one copy of *2 or *3 have an increased risk of bleeding compared to individuals without *2 or *3. In these instances, a lower warfarin maintenance dose may be required or alternative drugs may be considered.

Variation in the CYP2C9 gene can result in normal (NM), intermediate (IM) and poor (PM) drug-metabolizing phenotypes. In general, relative to the *1 allele (normal function), *2, *5, *8 and *11 alleles have decreased function, while *3, *6 and *13 alleles have no function.

The exact effect of a particular genotype on individual drugs can vary. In addition to genotype, the metabolism of drugs may be influenced by additional factors that include environmental, dietary and other medications; these factors and others should be considered prior to initialing a new therapy. All results must be interpreted in the context of other test results and clinical findings. Results do not rule out the possibility of other variant alleles in CYP2C9 or other variant alleles in other drug metabolism pathways. Patients should speak with their healthcare provider about the individual results of this test.

Molecular-based testing is highly accurate, but as in any laboratory test, rare diagnostic errors may occur.

This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration