4.9:
Dose-Response Relationship: Potency and Efficacy
Potency refers to the amount of drug required to generate a biological response.
In the dose–response curve of two antihypertensive drugs, candesartan and irbesartan, a lower EC50 value of candesartan suggests higher potency. This means that a lower dose of candesartan achieves the desired effect compared to irbesartan, which requires a higher dose.
However, since their Emax values are similar, both drugs are equally efficacious.
The efficacy of a drug depends on the number of drug–receptor complexes formed and the extent of receptor activation.
Maximal efficacy implies that the drugs occupy all receptors, and further increasing the drug concentration does not lead to an additional response.
Full agonists have high efficacy because they completely activate the receptors, triggering a full response.
In contrast, partial agonists exhibit lower efficacy as they activate the receptors to a lesser extent.
On the other hand, antagonists have zero efficacy. They do not activate the receptors but instead act as blockers. They reduce the number of available receptors for agonist binding or alter the receptor conformation, preventing effective agonist binding.
4.9:
Dose-Response Relationship: Potency and Efficacy
The potency of a drug is the measure of its ability to produce a biological response and can be compared by looking at the half-maximum effective concentration or EC50 values of different drugs. A lower EC50 value indicates higher potency of the drug. In the dose–response curve of two antihypertensive drugs, candesartan and irbesartan, a significant difference is observed in their EC50 values. A lower EC50 value for candesartan indicates that it is more potent than irbesartan, as it produces the same desired effect at a lower dose. It is noteworthy that both drugs exhibit similar maximum effect or Emax values, implying that they possess equal efficacy. Efficacy depends on the number of drug–receptor complexes formed and the extent of receptor activation. Maximal efficacy is achieved when all receptors are occupied, rendering further increases in drug concentration incapable of eliciting additional responses. Full agonists have high efficacy, as they activate receptors entirely and elicit a complete response. The efficacy of partial agonists is lower, as they activate receptors to a lesser extent. Antagonists, in contrast, exhibit zero efficacy by not activating the receptors. Instead, they act as blockers and either reduce the number of available receptors for agonist binding or induce conformational changes that prevent effective agonist binding. Overall, these factors play a crucial role in determining the efficacy and potency of drugs, which, in turn, can determine their usefulness in treating various medical conditions.