Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology 2

Question 1

The drug-receptor interaction for a full agonist is best described as:

Accepted Answer

High affinity and high intrinsic efficacy — binds receptor and produces maximum response

Answer

A full agonist has both high receptor affinity (binds the receptor well) and high intrinsic efficacy (produces the maximal pharmacological response upon binding). A partial agonist has affinity but submaximal efficacy. An antagonist has affinity but no efficacy.

Question 2

What is the therapeutic significance of the half-life (t½) of a drug?

Accepted Answer

It determines the time to reach steady state (approximately 4–5 half-lives) and dosing frequency

Answer

The half-life determines the time to reach steady-state concentration (4–5 × t½), time to wash out of the body, and appropriate dosing interval. Short t½ drugs require frequent dosing or sustained-release formulations. Steady state is where rate in = rate out.

Question 3

Which type of drug interaction involves one drug inducing CYP450 enzymes and increasing the metabolism of another drug?

Accepted Answer

Pharmacokinetic interaction — increased metabolism reducing drug levels

Answer

CYP450 enzyme induction (e.g., rifampin, carbamazepine, phenytoin) increases the rate of drug metabolism, reducing plasma levels of co-administered drugs that are CYP substrates. This can cause therapeutic failure. Pharmacodynamic interactions affect drug response at the receptor level.

Question 4

A pharmacist is checking a prescription for a patient with G6PD deficiency. Which drug class should be avoided due to risk of hemolytic anemia?

Accepted Answer

Primaquine and sulfonamides

Answer

G6PD deficiency impairs the hexose monophosphate shunt, reducing the ability to regenerate NADPH and protect red blood cells from oxidative stress. Drugs like primaquine, dapsone, sulfonamides, and nitrofurantoin cause oxidative hemolysis in G6PD-deficient patients.

Question 5

Which pharmacological principle explains why a combination of two beta-lactam antibiotics does not produce additive antibacterial activity?

Accepted Answer

Both drugs compete for the same PBP (penicillin-binding protein) targets — pharmacodynamic antagonism

Answer

Two beta-lactam antibiotics compete for the same penicillin-binding protein (PBP) targets. Combining them does not provide additional inhibition beyond what one drug achieves alone and may even antagonize effects. Combining drugs with different mechanisms (e.g., beta-lactam + aminoglycoside) provides synergy.

Saudi Prometric Pharmacist Practice Test

Saudi Prometric Pharmacist Practice Test

Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology 2