Reaction inhibitor

A reaction inhibitor is a substance that decreases the rate of, or prevents, a chemical reaction. A catalyst or an Enzyme activator, in contrast, is a substance that increases the rate of a chemical reaction.

## Contents

* 1 Examples
* 2 Inhibition of a catalyst
* 3 Inhibition and catalyst poisoning
* 4 Potency
* 5 See also
* 6 References

## Examples

* Added acetanilide slows the decomposition of drug-store hydrogen peroxide solution,[1] inhibiting the reaction

2H2O2 → 2H2O \+ O2, which is catalyzed by heat, light, and impurities.[2]

## Inhibition of a catalyst

An inhibitor can reduce the effectiveness of a catalyst in a catalysed reaction (either a non-biological catalyst or an enzyme). 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.[3]

Inhibitors of CYP can be classified by their potency, 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.) .[4]
* 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.) .[4]
* 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.) .[4]

## See also

* Enzyme inhibition
* Catalyst poisoning

## References

1. ↑ About acetanilide
2. ↑ The decomposition of hydrogen peroxide
3. ↑ "Drug Development and Drug Interactions: Table of Substrates, Inhibitors and Inducers". U.S. Food and Drug Administration. 26 May 2021. https://www.fda.gov/drugs/developmentapprovalprocess/developmentresources/druginteractionslabeling/ucm093664.htm.
4. ↑ 4.0 4.1 4.2 Center for Drug Evaluation and Research. "Drug Interactions & Labeling - Drug Development and Drug Interactions: Table of Substrates, Inhibitors and Inducers" (in en). https://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteractionsLabeling/ucm093664.htm#classInhibit.

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