Impact of Cytochrome P450 Enzymes on the Phase I Metabolism of Drugs

The cytochrome P450 (CYP) enzyme family is the major enzyme system catalyzing the phase I metabolism of xenobiotics, including pharmaceuticals and toxic compounds in the environment. A major part of the CYP-dependent xenobiotic metabolism is due to polymorphic and inducible enzymes, which may, quantitatively or qualitatively, alter or enhance drug metabolism and toxicity. Drug–drug interactions are major mechanisms caused by the inhibition and/or induction of CYP enzymes. Particularly, CYP monooxygenases catalyze hydroxylation reactions to form hydroxylated metabolites. The secondary metabolites are sometimes as active as the parent compound, or even more active. The aim of this review is to summarize some of the significative examples of common drugs used for the treatment of diverse diseases and underline the activity and/or toxicity of their metabolites.