Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology 1 — Questions and Answers
Question 1: Which functional group is responsible for the beta-lactam antibiotic activity in penicillin?
- The four-membered beta-lactam ring (Correct answer)
- The thiazolidine ring
- The side-chain amide group
- The carboxyl group at position 3
Correct answer: The four-membered beta-lactam ring
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?
- Statins (e.g., atorvastatin) (Correct answer)
- Fibrates (e.g., fenofibrate)
- Bile acid sequestrants (e.g., cholestyramine)
- Niacin (nicotinic acid)
Correct answer: Statins (e.g., atorvastatin)
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)?
- Irreversible inhibition of cyclooxygenase (COX-1 and COX-2) (Correct answer)
- Reversible inhibition of COX-2 only
- Inhibition of phospholipase A2
- Antagonism of prostaglandin receptors
Correct answer: Irreversible inhibition of cyclooxygenase (COX-1 and COX-2)
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?
- High lipophilicity (lipid solubility) (Correct answer)
- High molecular weight
- Low protein binding
- High pKa (strongly basic)
Correct answer: High lipophilicity (lipid solubility)
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?
- Saturable (zero-order at high doses) CYP2C9-mediated hydroxylation (Correct answer)
- First-order elimination via renal excretion
- Linear CYP3A4 metabolism
- Unchanged renal elimination
Correct answer: Saturable (zero-order at high doses) CYP2C9-mediated hydroxylation
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.
Question 6: Which chemical property allows a drug to be absorbed in the acidic environment of the stomach?
- Being a weak acid (low pKa) so it is un-ionized in acid — non-ionized form is lipid-soluble (Correct answer)
- Being a strong base with pKa >10
- Being highly ionized at gastric pH
- Having a very high molecular weight
Correct answer: Being a weak acid (low pKa) so it is un-ionized in acid — non-ionized form is lipid-soluble
The Henderson-Hasselbalch equation predicts ionization based on pKa and environmental pH. Weak acids (e.g., aspirin, pKa ~3.5) are predominantly un-ionized in the acidic stomach (pH 1–3), and un-ionized drugs are lipid-soluble and absorbed. Weak bases are ionized in acid and poorly absorbed.
Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology 1
Which functional group is responsible for the beta-lactam antibiotic activity in penicillin?