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Xenobiotic metabolism is divided into three phases. In phase I, enzymes such as cytochrome P450 oxidases introduce reactive or polar groups into xenobiotics. These modified compounds are then conjugated to polar compounds in phase II reactions. These reactions are catalysed by transferase enzymes such as glutathione S-transferases.
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug ...
A summary of the pathophysiology of a type 1 hypersensitivity reaction. Type I hypersensitivity can be further classified into immediate and late-phase reactions. Within minutes of exposure to an antigen, the immediate hypersensitivity occurs, releasing histamines and lipid mediators which are responsible for the initial allergic reaction response.
Type A: augmented pharmacological effects, which are dose-dependent and predictable [5]; Type A reactions, which constitute approximately 80% of adverse drug reactions, are usually a consequence of the drug's primary pharmacological effect (e.g., bleeding when using the anticoagulant warfarin) or a low therapeutic index of the drug (e.g., nausea from digoxin), and they are therefore predictable.
Allergic reactions may generally be divided into two components; the early phase reaction, and the late phase reaction. While the contribution to the development of symptoms from each of the phases varies greatly between diseases, both are usually present and provide us a framework for understanding allergic disease. [1] [2] [3] [4]
Metabolism (or biotransformation, or inactivation) – the chemical reactions of the drug and irreversible breakdown into metabolites (e.g. by metabolic enzymes such as cytochrome P450 or glucuronosyltransferase enzymes) Excretion – the removal of the substance or metabolites from the body.
Light-dependent reactions are certain photochemical reactions involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions: the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI) .
The cytochrome P450 proteins are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids, and other lipids. The enzyme encoded by this gene localizes to the endoplasmic reticulum ( ER ) and metabolizes procarcinogens such as polycyclic aromatic hydrocarbons and 17beta-estradiol .