BCSE Pharmacology and Toxicology 2 — Questions and Answers
Question 1: Which enzyme is primarily responsible for metabolizing warfarin in the liver?
- CYP2C9 (Correct answer)
- CYP3A4
- CYP2D6
- CYP1A2
Correct answer: CYP2C9
CYP2C9 is the primary hepatic enzyme responsible for the metabolism of the S-enantiomer of warfarin, which accounts for most of its anticoagulant activity.
Question 2: A patient presents with bradycardia, miosis, salivation, and urinary incontinence after exposure to an organophosphate pesticide. Which receptor is being overstimulated?
- Muscarinic acetylcholine receptor (Correct answer)
- Nicotinic acetylcholine receptor
- Alpha-1 adrenergic receptor
- Beta-2 adrenergic receptor
Correct answer: Muscarinic acetylcholine receptor
Organophosphates inhibit acetylcholinesterase, leading to accumulation of acetylcholine and overstimulation of muscarinic receptors, producing the classic SLUDGE syndrome.
Question 3: Which mechanism explains the development of tolerance to opioids with chronic use?
- Receptor desensitization and downregulation (Correct answer)
- Increased hepatic first-pass metabolism
- Upregulation of adenylyl cyclase activity
- Competitive antagonism at mu receptors
Correct answer: Receptor desensitization and downregulation
Chronic opioid exposure leads to desensitization and downregulation of mu-opioid receptors, requiring higher doses to achieve the same analgesic effect.
Question 4: A patient taking lithium develops polyuria and polydipsia. Which mechanism best explains this adverse effect?
- Lithium antagonizes ADH action at the collecting duct (Correct answer)
- Lithium increases ADH secretion from the posterior pituitary
- Lithium causes osmotic diuresis by glucosuria
- Lithium blocks aldosterone receptors in the distal tubule
Correct answer: Lithium antagonizes ADH action at the collecting duct
Lithium induces nephrogenic diabetes insipidus by inhibiting adenylyl cyclase in renal collecting duct cells, reducing the response to antidiuretic hormone (ADH).
Question 5: Which antidote is most appropriate for acetaminophen overdose presenting within 8 hours of ingestion?
- N-acetylcysteine (Correct answer)
- Flumazenil
- Naloxone
- Fomepizole
Correct answer: N-acetylcysteine
N-acetylcysteine replenishes glutathione stores and acts as a precursor to sulfate, detoxifying the hepatotoxic NAPQI metabolite produced during acetaminophen overdose.
Question 6: Aminoglycosides exert their antibacterial effect primarily by:
- Binding the 30S ribosomal subunit causing misreading of mRNA (Correct answer)
- Inhibiting the 50S ribosomal subunit and blocking peptide elongation
- Inhibiting cell wall synthesis by binding penicillin-binding proteins
- Disrupting the bacterial cell membrane integrity
Correct answer: Binding the 30S ribosomal subunit causing misreading of mRNA
Aminoglycosides irreversibly bind the 30S ribosomal subunit, causing misreading of the genetic code and insertion of incorrect amino acids, ultimately leading to bacterial cell death.
Question 7: Which adverse effect is most associated with long-term use of proton pump inhibitors (PPIs)?
- Hypomagnesemia (Correct answer)
- Hyperkalemia
- Hypercalcemia
- Hyperphosphatemia
Correct answer: Hypomagnesemia
Long-term PPI use reduces gastric acid secretion, impairing active magnesium absorption in the gut and leading to hypomagnesemia, which can cause cardiac arrhythmias and muscle cramps.
BCSE Pharmacology and Toxicology 2
Which enzyme is primarily responsible for metabolizing warfarin in the liver?