Drug metabolism, or biotransformation of drugs, is the process of chemical transformation of drugs in the body in order to facilitate their elimination. The main organ responsible for drug metabolism is the liver.
Biotransformation occurs in two phases. In phase I, oxidation, reduction and hydrolysis reactions occur, catalyzed by cytochrome P450 enzymes. These reactions convert drugs into more polar metabolites. In phase II, phase I metabolites are conjugated to endogenous molecules such as glucuronic acid, sulfates, glutathione and amino acids. This makes the metabolites even more water soluble for excretion in urine.
The metabolism of drugs is influenced by many factors: age, gender, genetic polymorphism, taking other drugs, liver and kidney diseases. Understanding biotransformation processes helps predict drug efficacy and toxicity and prevent drug interactions.