Cytochrome P450- (CYP450-) dependent monooxygenase occupies a pivotal role in the metabolism and detoxification process of endogenous and exogenous compounds [19]. CYP3A4 is the most abundant CYP450 and has clinical importance because it metabolizes numerous pharmaceutical agents [19]. It is highly expressed in the liver and intestine and represents 40% of the total hepatic and 80% of the total intestinal CYPs [20, 21]. CYP3A4 is also involved in the metabolism of endogenous substrates (retinoic and bile acids) and steroidal hormones (testosterone and estrogen) [22]. In addition, dietary and environmental chemicals such as aflatoxin B1 and some herbicides are also CYP3A4 substrates [23, 24]. The expression and activity of CYP3A4 are greatly impacted by many drugs and dietary chemicals such as rifampin (an antibiotic), carbamazepine (an anticonvulsant), glucocorticoids, and hyperforin (a major component of St. John’ wort) [25]. Individual variations in drug metabolism may be due to the differential expression of the CYP3A4 enzyme, induced by some of these compounds [20]. CYP3A4 protein expression in hepatocytes varies more than 50 folds among individuals, and the enzymatic activity varies by at least 20 folds [26]. Changes caused by drug-metabolizing enzymes (DMEs) are common and undesirable, and these enzymes influence the therapeutic effects of drugs, particularly those having a narrow therapeutic index [27]. Since CYP3A4 activity may be affected by some xenobiotics, it plays a crucial role in drug-drug interactions. For example, coadministration with rifampin, phenytoin, or carbamazepine may reduce plasma concentrations of a broad range of CYP3A4 drug substrates to less than a half [28].