FFICM Pharmacology Fundamentals 2 — Questions and Answers
Question 1: Which pharmacokinetic parameter describes the time for plasma concentration to fall by 50% after distribution equilibrium?
- Elimination half-life
- Distribution half-life
- Context-sensitive half-time (Correct answer)
- Mean residence time
Correct answer: Context-sensitive half-time
Context-sensitive half-time reflects the time for plasma concentration to halve after stopping an infusion, and varies with infusion duration unlike a simple elimination half-life.
Question 2: A patient on phenytoin requires an increased dose of vecuronium. The most likely pharmacokinetic explanation is:
- Increased renal excretion of vecuronium
- Induction of hepatic CYP450 enzymes increasing vecuronium metabolism (Correct answer)
- Reduced plasma protein binding
- Competitive antagonism at the neuromuscular junction
Correct answer: Induction of hepatic CYP450 enzymes increasing vecuronium metabolism
Phenytoin is a potent CYP450 inducer that accelerates hepatic metabolism of vecuronium, reducing its plasma concentration and duration of action.
Question 3: Which statement best describes zero-order kinetics?
- Elimination rate is proportional to drug concentration
- A constant amount of drug is eliminated per unit time regardless of concentration (Correct answer)
- Half-life remains constant across all plasma concentrations
- Drug clearance increases with rising plasma levels
Correct answer: A constant amount of drug is eliminated per unit time regardless of concentration
Zero-order kinetics occurs when elimination pathways are saturated, so a fixed amount (not fraction) of drug is cleared per unit time.
Question 4: The loading dose of a drug is primarily determined by:
- Clearance and desired effect duration
- Volume of distribution and target plasma concentration (Correct answer)
- Protein binding and renal function
- Bioavailability and first-pass metabolism
Correct answer: Volume of distribution and target plasma concentration
Loading dose = (Volume of distribution × Target plasma concentration) / Bioavailability, making Vd the dominant determinant.
Question 5: Which receptor type mediates the inotropic effects of dopamine at doses of 5–10 mcg/kg/min?
- Dopamine D1 receptors
- Alpha-1 adrenoceptors
- Beta-1 adrenoceptors (Correct answer)
- Beta-2 adrenoceptors
Correct answer: Beta-1 adrenoceptors
At intermediate doses (5–10 mcg/kg/min), dopamine predominantly stimulates beta-1 adrenoceptors, increasing heart rate and contractility.
Question 6: Which property of a drug most influences its ability to cross the blood-brain barrier?
- Molecular weight below 500 Da and high lipid solubility (Correct answer)
- High water solubility and low protein binding
- Large volume of distribution and long half-life
- Renal clearance and ionisation at physiological pH
Correct answer: Molecular weight below 500 Da and high lipid solubility
Drugs penetrate the BBB most readily when they are small, lipophilic, and largely unionised at physiological pH.
Question 7: A patient with hepatic failure is prescribed a drug with high hepatic extraction ratio (E > 0.7). What is the expected pharmacokinetic consequence?
- Reduced volume of distribution
- Markedly increased oral bioavailability due to reduced first-pass effect (Correct answer)
- Prolonged elimination half-life only
- No significant change as renal clearance compensates
Correct answer: Markedly increased oral bioavailability due to reduced first-pass effect
High extraction ratio drugs undergo extensive first-pass hepatic metabolism, so liver failure dramatically increases their systemic bioavailability after oral dosing.
FFICM Pharmacology Fundamentals 2
Which pharmacokinetic parameter describes the time for plasma concentration to fall by 50% after distribution equilibrium?