Drug Metabolism Enzymes and Reagents; Cyp 450s, Oxidases and Reductases

Phase I biotransformation reactions introduce or expose functional groups on the drug with the goal of increasing the polarity of the compound. Although Phase I drug metabolism occurs in most tissues, the primary and first pass site of metabolism occurs during hepatic circulation. Additional metabolism occurs in gastrointestinal epithelial, renal, skin, and lung tissues. Within cells, most phase I enzymes are located in the endoplasmic reticulum and thus are enriched in microsomal preparations.