Potency

Potency refers to the measure of drug activity expressed in terms of the amount required to produce an effect of given intensity. A highly potent drug (e.g., fentanyl, nicotine, or LSD) evokes a given response at low concentrations, while a drug of lower potency (e.g., ibuprofen) calls for higher concentrations to evoke the same response.

Factors Influencing Potency

Potency is influenced by various factors including the affinity (the ability of the drug to bind to its receptor), efficacy (the relationship between receptor occupancy and the ability to initiate a response at the molecular, cellular, tissue or system level) and the concentration of the drug at the receptor site.

Potency vs Efficacy

Potency should not be confused with efficacy. Efficacy refers to the maximum response achievable from a drug, while potency is the amount of drug needed to elicit a desired response. A drug can have high potency but low efficacy and vice versa.

Measurement of Potency

Potency is usually measured in terms of the concentration or amount of drug required to produce 50% of the drug's maximal effect (EC50). This is also known as the half maximal effective concentration.

See Also

• Pharmacodynamics
• Pharmacokinetics
• Dose-response relationship
• Therapeutic index

References

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