COMPREHENSIVE BASIC PHARMACOLOGY - 120 CHALLENGING MCQs

# COMPREHENSIVE BASIC PHARMACOLOGY - 120 CHALLENGING MCQs --- ## SECTION A: PHARMACOKINETICS (25 Questions) **1. Bioavailability is BEST defined as:** - A) Rate of drug absorption - B) Fraction of unchanged drug reaching systemic circulation - C) Drug concentration at receptor sites - D) Degree of protein binding **Answer: B** *Bioavailability (F) is the percentage of administered drug that reaches systemic circulation unchanged. IV route has 100% bioavailability by definition.* **2. A drug that undergoes extensive first-pass metabolism will show:** - A) Increased oral bioavailability - B) Reduced oral bioavailability - C) No effect on bioavailability - D) Increased half-life **Answer: B** *First-pass metabolism in the liver reduces the amount of drug reaching systemic circulation, decreasing oral bioavailability. Examples include nitroglycerin and propranolol.* **3. A patient with hepatic cirrhosis requires a drug with high first-pass metabolism. Which pharmacokinetic parameter change would you most expect?** - A) Decreased bioavailability - B) Increased bioavailability - C) No change in bioavailability - D) Decreased volume of distribution **Answer: B** *Hepatic cirrhosis reduces first-pass metabolism, so less drug is metabolized before reaching systemic circulation, resulting in increased bioavailability and risk of toxicity.* **4. Volume of distribution (Vd) increases when a drug is:** - A) Highly protein-bound - B) Highly water soluble - C) Highly lipid soluble - D) Administered intravenously **Answer: C** *Lipid-soluble drugs penetrate cell membranes easily and distribute widely into tissues, resulting in large Vd values.* **5. A drug has a volume of distribution (Vd) of 400L in a 70kg patient. What does this indicate?** - A) Drug is confined to plasma - B) Drug is confined to extracellular fluid - C) Drug is highly tissue-bound - D) Drug has poor absorption **Answer: C** *A Vd of 400L (much larger than total body water ~42L) indicates the drug is extensively distributed and bound to tissues outside the vascular compartment.* **6. Clearance is defined as:** - A) Fraction metabolized per hour - B) Volume of plasma cleared of drug per unit time - C) Rate of drug absorption - D) Protein binding capacity **Answer: B** *Clearance (CL) represents the volume of plasma from which drug is completely removed per unit time (mL/min or L/hr), reflecting elimination efficiency.* **7. The major determinant of half-life (t½) is:** - A) Bioavailability - B) Clearance and Vd - C) Protein binding only - D) Route of administration **Answer: B** *Half-life = (0.693 × Vd) / CL. It depends on both volume of distribution and clearance. Changes in either parameter affect t½.* **8. If a drug's half-life is 6 hours, approximately how long will it take to reach 97% steady-state concentration with continuous dosing?** - A) 12 hours - B) 18 hours - C) 24 hours - D) 30 hours **Answer: D** *Steady state is reached after approximately 5 half-lives (5 × 6 = 30 hours), which achieves about 97% of the final steady-state concentration.* **9. Zero-order kinetics means:** - A) A constant fraction is eliminated - B) A constant amount is eliminated - C) Elimination is concentration dependent - D) Drug never reaches steady state **Answer: B** *In zero-order kinetics, a fixed amount (not fraction) of drug is eliminated per unit time, regardless of concentration. Occurs with enzyme saturation (e.g., high-dose aspirin, alcohol, phenytoin).* **10. Which statement about zero-order kinetics is TRUE?** - A) A constant fraction of drug is eliminated per unit time - B) Half-life remains constant regardless of dose - C) Elimination rate is independent of drug concentration - D) Doubling the dose doubles the time to eliminate the drug **Answer: C** *In zero-order kinetics, a constant AMOUNT (not fraction) is eliminated per unit time, regardless of concentration. This occurs when elimination mechanisms are saturated.* **11. Steady-state concentration in continuous infusion mainly depends on:** - A) Loading dose - B) Half-life - C) Clearance - D) Route of administration **Answer: C** *Steady-state concentration (Css) = Infusion rate / Clearance. It's determined by the balance between input rate and elimination (clearance), not by Vd or t½.* **12. A loading dose is required to:** - A) Maintain steady state - B) Rapidly achieve therapeutic concentration - C) Reduce toxicity - D) Increase bioavailability **Answer: B** *Loading doses rapidly achieve therapeutic concentrations without waiting 5 half-lives. Loading dose = (Vd × Target concentration) / Bioavailability.* **13. A drug is 95% protein-bound. In a patient with hypoalbuminemia, what is the most likely consequence?** - A) Decreased total drug concentration, increased free drug concentration - B) Increased total drug concentration, decreased free drug concentration - C) Both total and free drug concentrations decrease - D) Decreased total d