Pharmacodynamic Mechanisms Flashcards

Which term describes a drug that binds to a receptor and produces a submaximal response regardless of dose?

Answer: Partial agonist

A partial agonist has intrinsic efficacy between 0 and 1, so it cannot produce the maximal response even at receptor saturation.

An inverse agonist differs from a neutral antagonist in that an inverse agonist:

Answer: Reduces receptor activity below constitutive baseline

An inverse agonist stabilizes the inactive receptor conformation, reducing constitutive (basal) receptor activity below the unliganded baseline.

The Emax in a dose-response curve represents:

Answer: The maximum possible effect of a drug

Emax is the ceiling effect — the greatest response a drug can produce regardless of how much dose is increased.

Two drugs are said to be equieffective when they:

Answer: Require the same dose to achieve any response

Equieffective doses produce the same magnitude of response and are the basis for comparing drug potency.

Receptor reserve (spare receptors) means that:

Answer: Maximum effect is achieved before all receptors are occupied

When receptor reserve exists, the system reaches Emax while a fraction of receptors remains unoccupied, allowing the drug to appear more potent than its Kd would predict.

Which pharmacodynamic parameter is most affected when a competitive antagonist is present?

Answer: EC50 of the agonist

A competitive antagonist shifts the agonist dose-response curve rightward, increasing EC50, while Emax remains achievable with higher agonist concentrations.

The phenomenon where prolonged receptor activation leads to decreased receptor number on the cell surface is called:

Answer: Receptor downregulation

Downregulation involves internalization and degradation of receptors following sustained agonist exposure, reducing overall cellular responsiveness.