What are the two primary phases of drug metabolism?

The two primary phases of drug metabolism are Phase I and Phase II.

Phase I metabolism primarily involves the modification of the drug molecule through chemical reactions such as oxidation, reduction, or hydrolysis. These reactions are mainly facilitated by enzymes known as cytochrome P450 enzymes. The primary goal of Phase I is to introduce or unmask functional groups on the drug molecule, which can enhance its polarity and prepare it for further conjugation processes in Phase II.

Phase II metabolism, on the other hand, involves the conjugation of the drug or its Phase I metabolites with endogenous substrates, such as glucuronic acid, sulfate, or glutathione. This process makes the drug more hydrophilic, promoting excretion from the body, usually via urine or bile. The conjugation reactions significantly increase the water solubility of the drug, which is crucial for its elimination from the body.

Together, these two phases are essential in the overall pharmacokinetic profile of a drug, dictating its efficacy, safety, and duration of action within the body. The combination of Phase I and Phase II ensures a comprehensive process for modifying and eliminating drugs, reducing toxicity, and balancing therapeutic effects.