Drug interactions: protein and CYP MCQs With Answer

Introduction

This collection of MCQs on drug interactions focusing on plasma protein binding and cytochrome P450 (CYP) mediated interactions is tailored for M.Pharm students studying Advanced Biopharmaceutics & Pharmacokinetics. The questions probe conceptual understanding and clinical implications: how protein binding displacement influences free drug concentration, clearance and volume of distribution; differences between high- and low-extraction drugs; mechanisms and consequences of CYP inhibition and induction; isoform-specific interactions and pharmacogenetic variability. Each question includes plausible distractors and clear answers to reinforce learning and prepare for examinations. Use these for self-assessment, group discussions, or as a revision tool to deepen grasp of clinically relevant pharmacokinetic interactions.

Q1. Which plasma protein primarily binds acidic drugs and influences displacement interactions for many commonly used acidic medications?

• Alpha-1-acid glycoprotein
• Gamma globulin
• Albumin
• Lipoprotein

Correct Answer: Albumin

Q2. For a low hepatic extraction ratio drug, an increase in unbound fraction (fu) due to displacement will most likely cause which of the following immediate changes assuming intrinsic clearance (CLint) is unchanged?

• Unbound steady-state concentration decreases while total concentration remains constant
• Unbound steady-state concentration remains approximately unchanged while total concentration decreases
• Both unbound and total concentrations increase proportionally
• Clearance decreases and unbound concentration increases

Correct Answer: Unbound steady-state concentration remains approximately unchanged while total concentration decreases

Q3. Which plasma protein predominantly binds basic drugs and is acute-phase reactant increasing during inflammation?

• Albumin
• Alpha-1-acid glycoprotein (AAG)
• Transferrin
• Fibrinogen

Correct Answer: Alpha-1-acid glycoprotein (AAG)

Q4. Grapefruit juice interacts with many orally administered drugs mainly by which mechanism?

• Induction of hepatic CYP2D6
• Inhibition of intestinal CYP3A4, often mechanism-based
• Activation of P-glycoprotein transporter
• Enhancement of renal tubular secretion

Correct Answer: Inhibition of intestinal CYP3A4, often mechanism-based

Q5. Which statement best describes a mechanism-based inhibitor (MBI) of a CYP enzyme?

• Reversible competitive binding that is overcome by increasing substrate concentration
• Irreversible or quasi-irreversible inactivation after metabolism of the inhibitor by the enzyme
• Non-selective induction of multiple CYP isoforms via nuclear receptors
• Transient inhibition with effect lasting minutes after drug clearance

Correct Answer: Irreversible or quasi-irreversible inactivation after metabolism of the inhibitor by the enzyme

Q6. Rifampin (rifampicin) affects plasma levels of co-administered drugs mainly by which mechanism?

• Competitive inhibition of CYP3A4
• Mechanism-based inactivation of intestinal CYP3A4 only
• Potent induction of multiple CYP enzymes via pregnane X receptor (PXR)
• Direct displacement from albumin binding sites

Correct Answer: Potent induction of multiple CYP enzymes via pregnane X receptor (PXR)

Q7. Which CYP isoform is most commonly involved in metabolism of approximately one-third of marketed drugs and is a frequent site of drug–drug interactions?

• CYP1A2
• CYP2C9
• CYP2D6
• CYP3A4

Correct Answer: CYP3A4

Q8. A drug that is a high hepatic extraction ratio (EH > 0.7) will have hepatic clearance primarily determined by which factor?

• Free fraction in plasma (fu)
• Intrinsic metabolic capacity (CLint)
• Hepatic blood flow (QH)
• Plasma protein binding to lipoproteins

Correct Answer: Hepatic blood flow (QH)

Q9. Two highly protein-bound drugs are co-administered and one displaces the other from albumin. Which clinical scenario is most likely if the displaced drug is a low-extraction drug with a narrow therapeutic index?

• No change in pharmacological effect because unbound concentration is strictly maintained
• Potential transient increase in free concentration and toxicity unless clearance rapidly compensates
• Immediate and sustained decrease in unbound concentration leading to therapeutic failure
• Irreversible binding to plasma proteins increasing duration of action

Correct Answer: Potential transient increase in free concentration and toxicity unless clearance rapidly compensates

Q10. Which equation represents hepatic clearance for a low-extraction drug under the well-stirred model?

• CLH = QH
• CLH = fu × CLint
• CLH = CLint / (1 + fu)
• CLH = Vd × ke

Correct Answer: CLH = fu × CLint

Q11. Which clinical example best illustrates a CYP-mediated interaction that increases parent drug exposure and risk of adverse effects?

• Co-administration of warfarin with rifampin leading to increased INR
• Co-administration of simvastatin with strong CYP3A4 inhibitor leading to increased statin levels and myopathy risk
• Co-administration of codeine with a CYP2D6 inhibitor leading to increased morphine formation
• Co-administration of oral contraceptive with St. John’s wort resulting in decreased contraceptive failure risk

Correct Answer: Co-administration of simvastatin with strong CYP3A4 inhibitor leading to increased statin levels and myopathy risk

Q12. CYP2D6 polymorphism can significantly affect response to which type of drug?

• Prodrugs requiring CYP2D6 for activation (e.g., codeine)
• Drugs exclusively eliminated unchanged in urine
• Drugs metabolized only by CYP3A4
• Compounds exclusively bound to alpha-1-acid glycoprotein

Correct Answer: Prodrugs requiring CYP2D6 for activation (e.g., codeine)

Q13. Which of the following best explains why displacement from plasma proteins rarely causes clinically significant increases in unbound drug concentration for most drugs?

• Displacement always reduces absorption so net effect is negligible
• Most drugs have large volume of distribution making plasma binding changes irrelevant
• For low-extraction drugs, increased fu raises clearance so unbound concentration often returns toward baseline
• Protein binding is irreversible for most therapeutic agents

Correct Answer: For low-extraction drugs, increased fu raises clearance so unbound concentration often returns toward baseline

Q14. A potent competitive inhibitor of CYP3A4 is co-administered with a CYP3A4 substrate. Which of the following is expected?

• Increase in substrate metabolic clearance
• Decrease in substrate plasma concentration and effect
• Increase in substrate plasma concentration and potential toxicity
• Induction of CYP3A4 expression decreasing substrate levels

Correct Answer: Increase in substrate plasma concentration and potential toxicity

Q15. Which process best describes enzyme induction by drugs such as phenobarbital or rifampin?

• Direct irreversible inhibition of CYP active site
• Transcriptional upregulation via nuclear receptors increasing enzyme synthesis
• Immediate competitive blockade of substrate binding
• Enhanced renal excretion of the enzymes

Correct Answer: Transcriptional upregulation via nuclear receptors increasing enzyme synthesis

Q16. In a patient with severe hepatic impairment, which effect on plasma protein binding and free fraction is most likely for an albumin-bound acidic drug?

• Increased albumin, decreased free fraction
• Decreased albumin, increased free fraction
• No change in albumin or free fraction
• Increased synthesis of AAG, decreased free fraction of acidic drugs

Correct Answer: Decreased albumin, increased free fraction

Q17. Which experimental parameter is most useful in predicting the clinical significance of a reversible CYP inhibitor in vivo?

• Solubility of the inhibitor in water
• Ki (inhibition constant) relative to expected inhibitor concentration at the enzyme site
• Protein binding of substrate only
• Half-life of the substrate drug in the absence of inhibitor

Correct Answer: Ki (inhibition constant) relative to expected inhibitor concentration at the enzyme site

Q18. Which statement regarding P-glycoprotein (P-gp) and CYP3A4 interactions is correct?

• P-gp and CYP3A4 are unrelated and never influence the same drug
• Many drugs are substrates of both P-gp and intestinal CYP3A4, so inhibition/induction can have additive effects on oral bioavailability
• P-gp only affects renal clearance and not oral absorption
• Inhibition of P-gp always decreases drug absorption

Correct Answer: Many drugs are substrates of both P-gp and intestinal CYP3A4, so inhibition/induction can have additive effects on oral bioavailability

Q19. Which clinical management strategy is most appropriate when starting a patient on a known strong CYP3A4 inducer with a narrow-therapeutic-index CYP3A4 substrate?

• No change is needed because induction effects are minor
• Reduce substrate dose immediately without monitoring
• Monitor therapeutic effect/concentration and adjust dose as induction reaches steady state (several days to weeks)
• Stop the substrate because induction is irreversible

Correct Answer: Monitor therapeutic effect/concentration and adjust dose as induction reaches steady state (several days to weeks)

Q20. A new drug is highly protein bound (99%) and is displaced by another co-administered agent raising fu to 99.9%. Which of the following best describes the expected change in total and unbound drug concentrations immediately after displacement (before physiological compensation)?

• Total concentration falls by ~10-fold while unbound concentration remains unchanged
• Total concentration decreases modestly while unbound concentration increases proportional to displacement
• Total concentration remains unchanged while unbound concentration decreases
• Both total and unbound concentrations fall to zero

Correct Answer: Total concentration decreases modestly while unbound concentration increases proportional to displacement

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