Test Details: Cytochrome P450 3A4 (CYP3A4) is the most important drug metabolizing enzyme in the liver, responsible for the oxidative metabolism of approximately 50% of clinically prescribed drugs. Therefore, genetic variation in CYP3A4 could potentially affect the pharmacokinetics, toxicity and clinical outcome of treatment with several drugs such as tacrolimus, cyclosporine, and statins. CYP3A4?22 genotype-based dosing could be helpful in improving drug therapy.