Understanding binding of drugs and apparent volume of distribution (Vd) is essential for pharmacokinetics in B. Pharm students. Drug–protein binding, tissue binding and physicochemical properties determine the free fraction, distribution, and apparent Vd, influencing dosing, loading dose, half-life, and drug interactions. Key concepts include plasma protein binding (albumin, alpha-1-acid glycoprotein), Vd calculation (Vd = dose / C0), units (L or L/kg), interpretation of small or large Vd, and clinical consequences of displacement and hypoalbuminemia. These MCQs cover calculations, concepts, and clinical scenarios. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What does the apparent volume of distribution (Vd) represent?
- The actual physical volume of the bloodstream
- The theoretical volume required to contain the total drug amount at the plasma concentration
- The volume of urine where drug is excreted
- The total body fat volume only
Correct Answer: The theoretical volume required to contain the total drug amount at the plasma concentration
Q2. Which equation correctly defines the initial apparent Vd after an IV bolus?
- Vd = Clearance × Half-life
- Vd = Dose / C0
- Vd = C0 / Dose
- Vd = Bioavailability × Dose
Correct Answer: Vd = Dose / C0
Q3. Which plasma protein primarily binds acidic drugs?
- Alpha-1-acid glycoprotein
- Transferrin
- Albumin
- Globulin
Correct Answer: Albumin
Q4. What is the unit commonly used to express Vd?
- mg/kg
- L or L/kg
- mg/L
- mEq/L
Correct Answer: L or L/kg
Q5. If a drug has a very large Vd (>> total body water), what does this indicate?
- Drug is confined to plasma
- Drug is extensively sequestered in tissues
- Drug is rapidly excreted unchanged in urine
- Drug has no protein binding
Correct Answer: Drug is extensively sequestered in tissues
Q6. How is the free fraction (fu) in plasma defined?
- fu = Bound drug concentration / Total concentration
- fu = Total concentration / Free drug concentration
- fu = Free drug concentration / Total drug concentration
- fu = Tissue concentration / Plasma concentration
Correct Answer: fu = Free drug concentration / Total drug concentration
Q7. A drug is 99% protein bound. What is its free fraction?
- 0.01 (1%)
- 0.10 (10%)
- 0.50 (50%)
- 0.99 (99%)
Correct Answer: 0.01 (1%)
Q8. Which factor will increase the apparent Vd of a lipophilic drug?
- Decreased tissue binding
- Increased plasma protein binding only
- Increased tissue binding and lipophilicity
- Decreased membrane permeability
Correct Answer: Increased tissue binding and lipophilicity
Q9. Which drug is typically associated with a large Vd?
- Heparin
- Digoxin
- Insulin (IV)
- Warfarin
Correct Answer: Digoxin
Q10. Which drug is largely confined to the plasma (low Vd)?
- Amiodarone
- Gentamicin
- Warfarin
- Chloroquine
Correct Answer: Warfarin
Q11. How does hypoalbuminemia generally affect free fraction of a highly albumin-bound acidic drug?
- Free fraction decreases
- Free fraction increases
- No change in free fraction
- Protein binding switches to alpha-1-acid glycoprotein
Correct Answer: Free fraction increases
Q12. For an IV drug, which formula is used to calculate loading dose?
- Loading dose = Clearance × Target concentration
- Loading dose = Vd × Target plasma concentration / F
- Loading dose = Half-life × Clearance
- Loading dose = Bioavailability × Clearance
Correct Answer: Loading dose = Vd × Target plasma concentration / F
Q13. What happens to total plasma concentration and free concentration immediately after displacement of a drug from plasma proteins?
- Total increases, free decreases
- Total decreases, free increases
- Total decreases, free unchanged initially
- Total decreases, free increases initially
Correct Answer: Total decreases, free increases
Q14. Which plasma protein preferentially binds basic drugs?
- Albumin
- Alpha-1-acid glycoprotein
- Fibrinogen
- Transferrin
Correct Answer: Alpha-1-acid glycoprotein
Q15. A 100 mg IV dose gives an initial plasma concentration (C0) of 2 mg/L. What is the apparent Vd?
- 200 L
- 50 L
- 0.02 L
- 2 L
Correct Answer: 50 L
Q16. Which statement about Vd and body composition is correct?
- Obesity always decreases Vd of lipophilic drugs
- Increased adipose tissue can increase Vd of lipophilic drugs
- Vd is independent of body composition
- Increased muscle mass reduces Vd of hydrophilic drugs
Correct Answer: Increased adipose tissue can increase Vd of lipophilic drugs
Q17. How does extensive tissue binding affect plasma half-life if clearance is unchanged?
- Half-life decreases
- Half-life increases
- No change in half-life
- Half-life becomes zero
Correct Answer: Half-life increases
Q18. Which observation suggests a drug is largely limited to the plasma compartment?
- Vd ≈ 0.1 L/kg
- Vd ≈ 1 L/kg
- Vd ≈ 10 L/kg
- Vd >> 100 L/kg
Correct Answer: Vd ≈ 0.1 L/kg
Q19. What is the clinical relevance of high protein binding for a drug with a narrow therapeutic index?
- Protein binding is irrelevant for toxicity
- Displacement interactions may cause marked increases in free drug and toxicity
- High protein binding always reduces efficacy
- High protein binding shortens half-life dramatically
Correct Answer: Displacement interactions may cause marked increases in free drug and toxicity
Q20. Which change would most likely increase total clearance for a low hepatic extraction drug?
- Decrease in free fraction
- Increase in free fraction
- Increase in plasma protein binding
- Decrease in intrinsic clearance only
Correct Answer: Increase in free fraction
Q21. Which statement correctly contrasts plasma protein binding and tissue binding?
- Plasma protein binding always increases Vd
- Tissue binding reduces Vd
- Plasma protein binding limits free fraction in plasma; tissue binding increases apparent Vd
- Both have identical effects on plasma clearance
Correct Answer: Plasma protein binding limits free fraction in plasma; tissue binding increases apparent Vd
Q22. Which parameter is directly used to compute loading dose for an IV drug?
- Clearance
- Volume of distribution (Vd)
- Half-life
- Renal clearance only
Correct Answer: Volume of distribution (Vd)
Q23. If Vd is 5 L and Vd is expressed per kg for a 70 kg adult, what is Vd (L/kg)?
- 0.071 L/kg
- 350 L/kg
- 5 L/kg
- 0.5 L/kg
Correct Answer: 0.071 L/kg
Q24. Which factor does NOT typically affect drug plasma protein binding?
- Concentration of binding proteins
- pH of plasma
- Presence of competing drugs
- Renal glomerular filtration rate directly
Correct Answer: Renal glomerular filtration rate directly
Q25. Why is Vd called an “apparent” volume?
- It measures actual anatomical volumes only
- Because it is a theoretical volume, not a real physiological space
- It is measured in molar units
- Because it equals total body water always
Correct Answer: Because it is a theoretical volume, not a real physiological space
Q26. Which clinical scenario can lead to increased free fraction and altered pharmacodynamics of a highly protein-bound drug?
- Hyperalbuminemia
- Hypoalbuminemia (e.g., liver disease)
- Increased hematocrit
- Dehydration only
Correct Answer: Hypoalbuminemia (e.g., liver disease)
Q27. Which is TRUE about the relationship between Vd and plasma concentration after a given dose?
- Higher Vd gives higher plasma concentration for the same dose
- Lower Vd gives lower plasma concentration for the same dose
- Higher Vd gives lower plasma concentration for the same dose
- Vd does not affect plasma concentration
Correct Answer: Higher Vd gives lower plasma concentration for the same dose
Q28. Which type of drug interaction involves competition for plasma protein binding sites?
- Metabolic induction
- Protein displacement interaction
- Renal secretion competition
- P-glycoprotein inhibition
Correct Answer: Protein displacement interaction
Q29. When might a clinician reduce the initial dose of a highly protein-bound drug?
- In a patient with elevated albumin
- In a patient with hypoalbuminemia and narrow therapeutic index
- In a patient with increased tissue binding only
- When Vd is extremely large but drug is inactive
Correct Answer: In a patient with hypoalbuminemia and narrow therapeutic index
Q30. Which best describes how tissue binding affects measurable plasma drug concentration?
- Strong tissue binding increases measured plasma concentration
- Strong tissue binding decreases measured plasma concentration for a given total dose
- Tissue binding has no effect on plasma concentrations
- Tissue binding converts drug to inactive metabolites
Correct Answer: Strong tissue binding decreases measured plasma concentration for a given total dose
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