Chapter 5
Pharmacokinetics: Drug Biotransformation
Drug Biotransformation: Overview
Drug biotransformation or metabolism entails chemical alteration of xenobiotics, either activating or deactivating their pharmacological properties.
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Phase I Oxidative Reactions: Overview
Phase I biotransformation or functionalization entails the chemical transformation of drugs into metabolites via oxidative, reductive, and or hydrolytic ...
Phase I Reactions: Oxidation of Aliphatic and Aromatic Carbon-Containing Systems
Phase I biotransformation primarily involves microsomal enzymes that catalyze oxidative reactions, using molecular oxygen and NADPH. Notably, only one ...
Phase I Reactions: Oxidation of Carbon-Heteroatom and Miscellaneous Systems
Carbon-nitrogen systems, encompassing aliphatic and alicyclic amines, undergo oxidative reactions.
Secondary and tertiary amines primarily undergo ...
Phase I Reactions: Reductive Reactions
Reductive reactions introduce electrons to drug molecules, affecting polar functional groups like hydroxy and amino, allowing subsequent biotransformation ...
Phase I Reactions: Hydrolytic Reactions
Hydrolysis is a chemical process where a compound is decomposed by reacting with water without altering its oxidation state.
This process plays a vital ...
Phase II Conjugation Reactions: Overview
Conjugation involves the covalent linkage of a conjugating reagent to drugs or their metabolites in the presence of a transferase enzyme.
These reagents ...
Phase II Reactions: Glucuronidation
Glucuronidation, a key phase II biotransformation reaction, involves the conjugation of glucuronic acid to xenobiotics or metabolites.
This process is ...
Phase II Reactions: Sulfation and Conjugation with α-Amino Acids
Sulfation, a phase II biotransformation reaction, involves the addition of a polar sulfate group to a drug.
The process is catalyzed by nonmicrosomal ...
Phase II Reactions: Glutathione Conjugation and Mercapturic Acid Formation
Glutathione is a tripeptide consisting of three amino acids – glutamic acid, cysteine, and glycine.
It plays a pivotal role in detoxification via ...
Phase II Reactions: Acetylation Reactions
Acetylation is a crucial phase II biotransformation process involving the addition of an acetyl group to a substrate.
It is similar to α-amino acid ...
Phase II Reactions: Methylation Reactions
Phase II methylation reactions involve the attachment of a methyl group to a substrate. This reaction is the reverse of the phase I demethylation. ...
Phase II Reactions: Miscellaneous Conjugation Reactions
Phase II biotransformations primarily involve detoxification processes where xenobiotics conjugate with endogenous substances.
The cyanide ion's ...
Factors Affecting Drug Biotransformation: Physicochemical and Chemical Properties of Drugs
Drug metabolism can be influenced by a drug's physicochemical properties, like molecular size and shape, which dictate the drug's interaction with ...
Factors Affecting Drug Biotransformation: Biological
Drug metabolism varies among species due to distinct enzyme systems and metabolic pathways.
Even within the same species, diverse strains can exhibit ...
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