Pharmacology Pharmacodynamic Mechanisms 3

Question 1

The therapeutic index (TI) is calculated as:

Accepted Answer

LD50 / ED50

Answer

TI = LD50 / ED50; a larger ratio indicates a wider margin of safety between effective and lethal doses.

Question 2

Allosteric modulators differ from orthosteric ligands because they:

Accepted Answer

Bind at a site distinct from the endogenous ligand binding site

Answer

Allosteric modulators bind to a topographically distinct site and alter receptor conformation to enhance or inhibit endogenous agonist activity.

Question 3

Which mechanism best explains the action of aspirin as an irreversible inhibitor of cyclooxygenase?

Accepted Answer

Covalent acetylation of a serine residue

Answer

Aspirin covalently acetylates Ser530 of COX-1 and Ser516 of COX-2, permanently inactivating the enzyme for its lifespan.

Question 4

A patient's response to a drug increases rather than decreases with repeated administration. This is best described as:

Accepted Answer

Sensitization (reverse tolerance)

Answer

Sensitization refers to an augmented response following repeated drug exposure, seen with stimulants like cocaine and amphetamines.

Question 5

Which receptor family primarily signals through G-protein–mediated second messenger cascades?

Accepted Answer

G-protein–coupled receptors (GPCRs)

Answer

GPCRs (7-TM receptors) couple to heterotrimeric G-proteins that modulate intracellular effectors such as adenylyl cyclase and phospholipase C.

Pharmacology Practice Test