Potency and efficacy are frequently mixed up, but these terms are not synonymous and used misleadingly. However, it is foremost significant to differentiate the potency and efficacy of a drug for clinical use. Independently, potency and efficacy of drug may vary. Probably from graded dose-response curves, two key properties of drugs can be determined, those are potency and efficacy. Certainly, you may clearly understand the difference between potency and efficacy after reading this article.
1. Definition of Potency and Efficacy
Potency is a comparative measure of different doses of two drugs that are needed to produce the same pharmacological effect. It is also known as drug strength. Simply, Potency is the amount of drug needed to produce a certain response .
In other words, Potency refers to the concentration (EC50) or dose (ED50) of a drug required to produce 50% of that drug’s maximal effect .
Certainly, more the ED 50 of a drug, less the potency and Less the ED50, more the potency.
Potency is a measure of the amount of drug necessary to produce an effect of a given magnitude .
On the other hand, Efficacy is the ability of a drug after binding with receptors to initiate change which leads to certain effects. Simply, Efficacy (Emax) is the capacity of a drug to produce a maximum response. Also, it is known as maximal efficacy.
In other words, Efficacy is the maximal response that can be elicited by the drug .
In other words, Efficacy is the ability of a drug to elicit a physiologic response when it interacts with a receptor.
2. The core theme of potency and efficacy
Potency is absolute potency. Whereas, efficacy is therapeutic potency.
3. Estimation of potency and efficacy
Potency is estimated by comparing dose (ED50). On the other hand, efficacy is estimated by comparing differences in the highest response at high drug concentrations or doses.
4. Depending factor
Potency of a drug depends on the affinity of the receptors to bind the drug and how effectively the drug-receptor interaction leads to clinical response . Whereas, efficacy depends on the concentration at the site of action, the number of drug-receptor binding, psychological factors and, the efficiency of the coupling of receptor activation to cellular responses.
5. Decisive component
Potency is a decisive component to choose the dose of the drug. While efficacy is a decisive component to choose a drug among other drugs of the same kind.
6. Relation with clinical effectiveness
The clinical effectiveness of a drug does not depend on its potency. On the other hand, the clinical effectiveness of a drug depends on its efficacy.
Potency is less significant than efficacy. While efficacy is more significant than drug potency. Certainly, a drug with greater efficacy than greater potency is more therapeutically beneficial.
Potency of a drug may be beneficial in the dosage forms design. While efficacy may be beneficial in the determination of clinical effectiveness of a drug.
9. Example of potency and efficacy
Generally, 500 mg of Paracetamol and 30 mg of morphine used as an analgesic. Here, a small dose of morphine requires to produce an analgesic effect. Thus, morphine is more potent analgesic than Paracetamol.
On the other hand, morphine produces an optimum level of analgesia which is not possible with any dose of aspirin. Hence, morphine has more efficacy than aspirin. Likewise, is furosemide a diuretic has more capacity to eliminate more salt and fluid from urine than metolazone. So, furosemide has greater efficacy than metolazone.
Summary of the difference between Potency and Efficacy
|Potency is the amount of drug needed to produce a certain response.||Efficacy is the ability of a drug to elicit a physiologic response when it interacts with a receptor.|
|It is absolute potency.||It is therapeutic potency.|
|Potency is estimated by comparing dose (ED50).||Efficacy is estimated by comparing differences in the highest response at high drug concentrations or doses.|
|It depends on the affinity as well as efficacy.||It depends on the concentration at the site of action, the number of drug-receptor binding, psychological factors and the efficiency of the coupling of receptor activation to cellular responses.|
|Potency is a decisive component to choose the dose of the drug.||Efficacy is a decisive component to choose a drug.|
|It does not depend on its potency.||It depends on its efficacy.|
|Less significant than efficacy.||More significant than drug potency.|
|Beneficial in the dosage forms design.||Beneficial in the determination of clinical effectiveness of a drug.|
|Morphine is more potent analgesic than Paracetamol.||Morphine has more efficacy than aspirin.|
Also, you may read:
- Tripathi, K. D. (2013). Essentials of medical pharmacology (7th edition). New Delhi: Jaypee Brothers Medical Publishers.
- Katzung, B. G., Masters, S. B., & Trevor, A. J. (2009). Basic & clinical pharmacology (11th edition.). New York: McGraw-Hill.
- Howland, R. D., & Mycek, M. J. (2006). Lippincott’s illustrated reviews: Pharmacology. Philadelphia: J.B. Lippincott Williams & Wilkins.
- Brandt N. (2013) Dose: Intensity, Response. In: Gellman M.D., Turner J.R. (eds) Encyclopedia of Behavioral Medicine. Springer, New York, NY