Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology

Question 1

Which functional group is responsible for the beta-lactam antibiotic activity in penicillin?

Accepted Answer

The four-membered beta-lactam ring

Answer

The beta-lactam ring (4-membered cyclic amide) is the pharmacophore of penicillins and all beta-lactam antibiotics. It irreversibly inhibits bacterial transpeptidases (PBPs) required for cell wall synthesis. Hydrolysis of this ring by beta-lactamases inactivates the drug.

Question 2

Which drug class inhibits HMG-CoA reductase to lower plasma cholesterol?

Accepted Answer

Statins (e.g., atorvastatin)

Answer

Statins competitively inhibit HMG-CoA reductase, the rate-limiting enzyme in hepatic cholesterol synthesis. Reduced intracellular cholesterol upregulates hepatic LDL receptors, increasing LDL clearance from plasma. They are the most effective drugs for reducing LDL cholesterol.

Question 3

What is the mechanism of action of aspirin (acetylsalicylic acid)?

Accepted Answer

Irreversible inhibition of cyclooxygenase (COX-1 and COX-2)

Answer

Aspirin irreversibly acetylates a serine residue in the active site of both COX-1 and COX-2 enzymes, permanently blocking prostaglandin and thromboxane synthesis. Because platelets lack a nucleus, they cannot synthesize new COX, so inhibition lasts the platelet's lifetime (7–10 days).

Question 4

Which property of a drug determines its distribution to tissues with high lipid content such as the brain?

Accepted Answer

High lipophilicity (lipid solubility)

Answer

Lipophilic (fat-soluble) drugs readily cross lipid membranes including the blood-brain barrier and distribute into adipose tissue. The partition coefficient (log P) measures lipophilicity — higher values indicate greater distribution into lipid-rich tissues.

Question 5

A pharmacist is reviewing a prescription for phenytoin. Which metabolic pathway is responsible for phenytoin's non-linear pharmacokinetics?

Accepted Answer

Saturable (zero-order at high doses) CYP2C9-mediated hydroxylation

Answer

Phenytoin undergoes saturable hepatic hydroxylation via CYP2C9. At therapeutic doses the enzymes become saturated, causing zero-order kinetics — small dose increases cause disproportionately large rises in plasma levels. This makes phenytoin dosing difficult and toxicity common.

Saudi Prometric Pharmacist Practice Test

Saudi Prometric Pharmacist Practice Test

Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology