PTCB Pharmacology #3 3 — Questions and Answers
Question 1: Which CYP enzyme is responsible for metabolizing the largest proportion of drugs?
- CYP1A2
- CYP2D6
- CYP3A4 (Correct answer)
- CYP2C9
Correct answer: CYP3A4
CYP3A4 is the most abundant hepatic cytochrome P450 enzyme, responsible for metabolizing approximately 50% of all drugs, including statins, benzodiazepines, calcium channel blockers, and many others.
Question 2: A CYP enzyme "inducer" would be expected to:
- Increase plasma levels of co-administered drugs metabolized by that enzyme
- Decrease plasma levels of co-administered drugs metabolized by that enzyme (Correct answer)
- Block the enzyme completely
- Have no clinical significance
Correct answer: Decrease plasma levels of co-administered drugs metabolized by that enzyme
Enzyme inducers (e.g., rifampin, carbamazepine, St. John's Wort) increase CYP enzyme expression, accelerating metabolism and DECREASING plasma levels of affected drugs, potentially causing therapeutic failure.
Question 3: Which of the following is a major contraindication for the use of metformin?
- Mild hypertension
- eGFR < 30 mL/min/1.73m² (severe renal impairment) (Correct answer)
- Age over 65 years
- Type 1 diabetes
Correct answer: eGFR < 30 mL/min/1.73m² (severe renal impairment)
Metformin is contraindicated in severe renal impairment (eGFR < 30) due to the risk of lactic acidosis from reduced elimination. It should be used cautiously when eGFR is 30–45 and is generally avoided when < 30.
Question 4: Grapefruit juice interacts with many drugs because it:
- Decreases gastric pH
- Induces CYP3A4 in the liver
- Inhibits intestinal CYP3A4 and P-glycoprotein (Correct answer)
- Increases renal drug elimination
Correct answer: Inhibits intestinal CYP3A4 and P-glycoprotein
Grapefruit juice contains furanocoumarins that irreversibly inhibit CYP3A4 in the intestinal wall and P-gp, increasing bioavailability of many drugs (statins, calcium channel blockers, immunosuppressants).
Question 5: Which drug class do "-gliptin" suffix drugs belong to?
- Biguanides
- SGLT-2 inhibitors
- Sulfonylureas
- DPP-4 inhibitors (Correct answer)
Correct answer: DPP-4 inhibitors
DPP-4 inhibitors (dipeptidyl peptidase-4 inhibitors) end in "-gliptin" (sitagliptin, saxagliptin, alogliptin, linagliptin). They prolong incretin activity, enhancing glucose-dependent insulin secretion.
Question 6: What is the mechanism by which SGLT-2 inhibitors (e.g., empagliflozin) lower blood glucose?
- Stimulate insulin secretion from beta cells
- Inhibit glucagon secretion
- Block sodium-glucose cotransporter-2 in the kidney to promote glucose excretion in urine (Correct answer)
- Reduce hepatic glucose production
Correct answer: Block sodium-glucose cotransporter-2 in the kidney to promote glucose excretion in urine
SGLT-2 inhibitors block the sodium-glucose cotransporter-2 in the proximal renal tubule, reducing renal glucose reabsorption and promoting glucosuria (glucose excretion in urine), lowering blood glucose levels.
PTCB Pharmacology #3 3
Which CYP enzyme is responsible for metabolizing the largest proportion of drugs?