Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology 3 — Questions and Answers
Question 1: Digoxin's positive inotropic effect is mediated by which mechanism?
- Inhibition of Na+/K+-ATPase pump, increasing intracellular Na+, which increases intracellular Ca2+ via Na+/Ca2+ exchange (Correct answer)
- Direct stimulation of myocardial beta-1 receptors
- Inhibition of phosphodiesterase increasing cAMP
- Blockade of cardiac potassium channels
Correct answer: Inhibition of Na+/K+-ATPase pump, increasing intracellular Na+, which increases intracellular Ca2+ via Na+/Ca2+ exchange
Digoxin inhibits the Na+/K+-ATPase pump. This raises intracellular Na+, which reduces Na+/Ca2+ exchanger (NCX) activity, increasing intracellular Ca2+, and thus increasing myocardial contractility. Digoxin also increases vagal tone, slowing AV conduction (used in AF rate control).
Question 2: Which drug is used to reverse the effects of benzodiazepine overdose?
- Flumazenil — competitive GABA-A receptor antagonist (Correct answer)
- Naloxone — opioid receptor antagonist
- Physostigmine — acetylcholinesterase inhibitor
- Protamine sulfate — heparin antagonist
Correct answer: Flumazenil — competitive GABA-A receptor antagonist
Flumazenil is a competitive benzodiazepine antagonist at the GABA-A receptor. It rapidly reverses benzodiazepine-induced sedation, respiratory depression, and coma. Its short half-life (1 hour) means re-sedation can occur, requiring repeat dosing or monitoring.
Question 3: A pharmacist is counseling a patient about tamoxifen for breast cancer prevention. What is the mechanism of action of tamoxifen?
- Selective estrogen receptor modulator (SERM) — antagonist in breast tissue, partial agonist in uterus and bone (Correct answer)
- Pure estrogen receptor antagonist in all tissues
- Aromatase inhibitor preventing estrogen synthesis
- Progesterone receptor agonist
Correct answer: Selective estrogen receptor modulator (SERM) — antagonist in breast tissue, partial agonist in uterus and bone
Tamoxifen is a SERM with tissue-selective estrogen receptor effects. In breast tissue, it antagonizes estrogen, inhibiting estrogen receptor-positive (ER+) breast cancer growth. In the uterus, it acts as a partial agonist, increasing risk of endometrial cancer. In bone, it acts as an agonist, protecting bone density.
Question 4: Which receptor type mediates the therapeutic bronchodilation effect of salbutamol (albuterol)?
- Beta-2 adrenergic receptor in bronchial smooth muscle (Correct answer)
- Beta-1 adrenergic receptor in the heart
- Alpha-1 adrenergic receptor in blood vessels
- Muscarinic M3 receptor in bronchi
Correct answer: Beta-2 adrenergic receptor in bronchial smooth muscle
Salbutamol is a selective beta-2 adrenergic agonist. Activation of beta-2 receptors in bronchial smooth muscle activates adenylyl cyclase → increases cAMP → activates PKA → phosphorylates myosin light chain kinase → causes bronchial smooth muscle relaxation (bronchodilation).
Question 5: A pharmacist is reviewing the structure-activity relationships (SAR) of opioids. Which structural feature is essential for opioid receptor binding?
- A phenolic hydroxyl group at position 3 and a tertiary nitrogen (Correct answer)
- A beta-lactam ring
- A fluorine substituent on the benzene ring
- A sulfonic acid group
Correct answer: A phenolic hydroxyl group at position 3 and a tertiary nitrogen
The classic morphine-like opioid pharmacophore requires: a phenolic hydroxyl at C-3 (essential for mu-receptor affinity), a hydroxyl at C-6, and a basic nitrogen. Methylation of the C-3 hydroxyl (as in codeine) reduces potency. This SAR guides opioid drug design.
Question 6: Which phenomenon explains why repeated morphine administration leads to progressively higher doses being needed for pain relief?
- Pharmacodynamic tolerance — receptor downregulation and desensitization (Correct answer)
- Pharmacokinetic tolerance — increased metabolism
- Tachyphylaxis — rapid acute tolerance
- Cross-tolerance only with other opioids
Correct answer: Pharmacodynamic tolerance — receptor downregulation and desensitization
Chronic opioid use leads to receptor desensitization (phosphorylation and uncoupling from G proteins), downregulation (reduced receptor number), and tolerance at second messenger levels. Both pharmacodynamic and pharmacokinetic (induction of CYP3A4) tolerance contribute to reduced opioid effect.
Saudi Prometric Pharmacist Pharmaceutical Chemistry and Pharmacology 3
Digoxin's positive inotropic effect is mediated by which mechanism?