A reaction inhibitor is a
substance that decreases the rate of, or prevents, a
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
.
A catalyst, in contrast, is a substance that increases the rate of a chemical reaction.
Examples
* Added
acetanilide
Acetanilide is an odourless solid chemical of leaf or flake-like appearance. It is also known as ''N''-phenylacetamide, acetanil, or acetanilid, and was formerly known by the trade name Antifebrin.
Preparation and properties
Acetanilide can be ...
slows the decomposition of drug-store
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
solution, inhibiting the reaction
2 → 2 + , which is catalyzed by heat, light, and impurities.
[The decomposition of hydrogen peroxide]
Inhibition of a catalyst
An inhibitor can reduce the effectiveness of a
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
in a catalysed reaction (either a non-biological catalyst or an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
). E.g., if a compound is so similar to (one of) the reactants that it can bind to the active site of a catalyst but does not undergo a catalytic reaction then that catalyst molecule cannot perform its job because the active site is occupied. When the inhibitor is released, the catalyst is again available for reaction.
Inhibition and catalyst poisoning
Inhibition should be distinguished from catalyst poisoning. An inhibitor only hinders the working of a catalyst without changing it, whilst in catalyst poisoning the catalyst undergoes a chemical reaction that is irreversible in the environment in question (the active catalyst may only be regained by a separate process).
Potency
Index inhibitors or simplified as inhibitor predictably inhibit metabolism via a given
pathway and are commonly used in prospective clinical
drug-drug interaction studies.
Inhibitors of
CYP can be classified by their
potency
Potency may refer to:
* Potency (pharmacology), a measure of the activity of a drug in a biological system
* Virility
* Cell potency, a measure of the differentiation potential of stem cells
* In homeopathic dilutions, potency is a measure of how ...
, such as:
*Strong inhibitor being one that causes at least a 5-fold increase in the plasma
AUC values, or more than 80% decrease in
clearance of
substrates ( Over 1.8 times slower than usual clearance rate.) .
*Moderate inhibitor being one that causes at least a 2-fold increase in the plasma AUC values, or 50-80% decrease in clearance of substrates ( At least 1.5-1.8 times slower than usual clearance speed.) .
*Weak inhibitor being one that causes at least a 1.25-fold but less than 2-fold increase in the plasma AUC values, or 20-50% decrease in clearance of substrates ( At least 1.2-1.5 times slower than usual clearance rate.) .
See also
*
Enzyme inhibition
An enzyme inhibitor is a molecule that binds to an enzyme and blocks its activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which substrate molecules are converted into products. An enzyme facilitates a sp ...
*
Catalyst poisoning Catalyst poisoning refers to the partial or total deactivation of a catalyst by a chemical compound. Poisoning refers specifically to chemical deactivation, rather than other mechanisms of catalyst degradation such as thermal decomposition or physic ...
References
Catalysis
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