The Cytochrome P450 enzymes play a major role in the metabolism of drugs. A change in their activity, either by inhibition or induction, may have significant effects in the pharmacokinetics and therefore in pharmacologic effects of the compounds. While inhibition of CYP450 enzymes responsible for the metabolism of a co-medicated drug may raise its concentration to a toxic level, induction of CYP450 may hasten the elimination of the co-medicated drug to sub-therapeutic levels leading to dramatic decrease of its pharmacological response. These drug-drug interactions (DDI) are critical safety concerns in preclinical and clinical development by the regulatory agencies. Therefore early stage screening of compounds for potential DDI using in vitro techniques becomes indispensable in order to reduce late stage compound attrition.