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Potency (pharmacology)
Encyclopedia
In the field of pharmacology
, potency is a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity. A highly potent drug (e.g., morphine
, alprazolam
, chlorpromazine
) evokes a larger response at low concentrations, while a drug of lower potency (ibuprofen
, acetylsalicylic acid) evokes a small response at low concentrations. It is proportional to affinity and efficacy
.
Affinity is the ability of the drug to bind to a receptor. Efficacy
is the relationship between receptor occupancy and the ability to initiate a response at the molecular, cellular, tissue or system level. The response is equal to the effect, or (E), and depends on both the drug binding and the drug-bound receptor then producing a response; thus, potency depends on both affinity and efficacy. The agonist, the ligand, drug or hormone that binds to the receptor and initiates the response is usually abbreviated A or D. Below a certain concentration of agonist ([A]), E is too low to measure but at higher concentrations it becomes appreciable and rises with increasing agonist concentration [A] until at sufficiently high concentrations it can no longer be increased by raising [A] and asymptotes to a maximum Emax.
The Emax is the maximum possible effect for the agonist. The concentration of A at which E is 50% of Emax is termed the half maximal effective concentration and is abbreviated [A]50, or more commonly EC50. The term "potency" refers to the [A]50 value. The lower the [A]50, the less the concentration of a drug is required to produce 50% of maximum effect and the higher the potency.
Higher potency does not necessarily mean more side effects
.
Pharmacology
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...
, potency is a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity. A highly potent drug (e.g., morphine
Morphine
Morphine is a potent opiate analgesic medication and is considered to be the prototypical opioid. It was first isolated in 1804 by Friedrich Sertürner, first distributed by same in 1817, and first commercially sold by Merck in 1827, which at the time was a single small chemists' shop. It was more...
, alprazolam
Alprazolam
Alprazolam is a short-acting anxiolytic of the benzodiazepine class of psychoactive drugs. Alprazolam, like other benzodiazepines, binds to specific sites on the GABAA gamma-amino-butyric acid receptor...
, chlorpromazine
Chlorpromazine
Chlorpromazine is a typical antipsychotic...
) evokes a larger response at low concentrations, while a drug of lower potency (ibuprofen
Ibuprofen
Ibuprofen is a nonsteroidal anti-inflammatory drug used for relief of symptoms of arthritis, fever, as an analgesic , especially where there is an inflammatory component, and dysmenorrhea....
, acetylsalicylic acid) evokes a small response at low concentrations. It is proportional to affinity and efficacy
Intrinsic activity
Intrinsic activity or efficacy refers to the relative ability of a drug-receptor complex to produce a maximum functional response. This must be distinguished from the affinity, which is a measure of the ability of the drug to bind to its molecular target, and the EC50, which is a measure of the...
.
Affinity is the ability of the drug to bind to a receptor. Efficacy
Intrinsic activity
Intrinsic activity or efficacy refers to the relative ability of a drug-receptor complex to produce a maximum functional response. This must be distinguished from the affinity, which is a measure of the ability of the drug to bind to its molecular target, and the EC50, which is a measure of the...
is the relationship between receptor occupancy and the ability to initiate a response at the molecular, cellular, tissue or system level. The response is equal to the effect, or (E), and depends on both the drug binding and the drug-bound receptor then producing a response; thus, potency depends on both affinity and efficacy. The agonist, the ligand, drug or hormone that binds to the receptor and initiates the response is usually abbreviated A or D. Below a certain concentration of agonist ([A]), E is too low to measure but at higher concentrations it becomes appreciable and rises with increasing agonist concentration [A] until at sufficiently high concentrations it can no longer be increased by raising [A] and asymptotes to a maximum Emax.
The Emax is the maximum possible effect for the agonist. The concentration of A at which E is 50% of Emax is termed the half maximal effective concentration and is abbreviated [A]50, or more commonly EC50. The term "potency" refers to the [A]50 value. The lower the [A]50, the less the concentration of a drug is required to produce 50% of maximum effect and the higher the potency.
Higher potency does not necessarily mean more side effects
Adverse drug reaction
An adverse drug reaction is an expression that describes harm associated with the use of given medications at a normal dosage. ADRs may occur following a single dose or prolonged administration of a drug or result from the combination of two or more drugs...
.