<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A series of chemical modifications of a drug compound by enzymatic activity that make the substrate (drug) more water soluble to allow its clearance from the body. Drug metabolism occurs in two phases: Phase I (biotransformation) involves oxidation, hydroxylation reduction, and hydrolysis. Phase II (conjugation) involves synthesis and conjugation.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>