FPGEE Pharmacokinetics 2 — Questions and Answers
Question 1: A drug has a volume of distribution (Vd) of 350 L in a 70 kg patient. What does this suggest about the drug's distribution?
- The drug is confined mainly to plasma
- The drug is extensively distributed into tissues (Correct answer)
- The drug has moderate protein binding in plasma
- The drug undergoes extensive first-pass metabolism
Correct answer: The drug is extensively distributed into tissues
A Vd of 350 L far exceeds total body water (~42 L), indicating extensive tissue distribution rather than plasma confinement.
Question 2: Which pharmacokinetic parameter best predicts drug accumulation during multiple dosing?
- Volume of distribution
- Half-life (Correct answer)
- Bioavailability
- Protein binding fraction
Correct answer: Half-life
Half-life determines accumulation because it dictates how much drug remains before each subsequent dose.
Question 3: A patient with renal failure has a creatinine clearance of 15 mL/min (normal ~120 mL/min). For a drug that is 80% renally excreted unchanged, how should dosing be adjusted?
- No adjustment needed
- Reduce dose or extend interval significantly (Correct answer)
- Increase dose to compensate for poor absorption
- Switch to IV route only
Correct answer: Reduce dose or extend interval significantly
An 87.5% reduction in renal clearance for a predominantly renally excreted drug requires substantial dose reduction or interval extension to avoid toxicity.
Question 4: Which of the following best describes zero-order kinetics?
- A constant fraction of drug is eliminated per unit time
- A constant amount of drug is eliminated per unit time (Correct answer)
- Elimination rate increases proportionally with concentration
- Half-life shortens as dose increases
Correct answer: A constant amount of drug is eliminated per unit time
Zero-order kinetics occurs when elimination mechanisms are saturated and a fixed amount (not fraction) is eliminated per unit time.
Question 5: The area under the curve (AUC) is most directly used to calculate which parameter?
- Volume of distribution
- Half-life
- Systemic clearance (Correct answer)
- Time to peak concentration
Correct answer: Systemic clearance
Systemic clearance (CL) = Dose / AUC for IV administration, making AUC the direct input for calculating clearance.
Question 6: A drug with a high extraction ratio is given orally. Which factor most significantly reduces its bioavailability?
- Gastrointestinal pH
- First-pass hepatic metabolism (Correct answer)
- Renal clearance
- Plasma protein binding
Correct answer: First-pass hepatic metabolism
High hepatic extraction ratio drugs undergo extensive first-pass metabolism, dramatically reducing oral bioavailability before reaching systemic circulation.
Question 7: What happens to the steady-state concentration (Css) if the dosing interval is halved while keeping the dose the same?
- Css doubles (Correct answer)
- Css is unchanged
- Css halves
- Css increases fourfold
Correct answer: Css doubles
Halving the dosing interval doubles the dosing rate (mg/hr), which doubles Css since Css = Dosing rate / Clearance.
FPGEE Pharmacokinetics 2
A drug has a volume of distribution (Vd) of 350 L in a 70 kg patient.
What does this suggest about the drug's distribution?