Drug Interactions & PK-PD Modeling MCQs With Answer

Drug Interactions & PK-PD Modeling MCQs With Answer

This MCQ collection is designed for M.Pharm students enrolled in Advanced Biopharmaceutics & Pharmacokinetics (MIP 201T). The questions emphasize mechanistic understanding of pharmacokinetic drug–drug interactions (absorption, distribution, metabolism, excretion), enzyme inhibition and induction kinetics, transporter-mediated interactions, and their impact on exposure. The PK-PD section covers compartmental and non-compartmental concepts, concentration–effect relationships (Emax, EC50, Hill coefficient), target-mediated drug disposition, population PK/PD, model evaluation, and PK/PD indices for antimicrobials. Each item includes plausible distractors and a clear correct answer to aid revision, self-assessment, and preparation for advanced examinations and research applications.

Q1. Which feature best characterizes mechanism-based (time-dependent) inhibition of a metabolic enzyme?

• Rapid reversible inhibition that dissipates as inhibitor concentration falls
• Formation of a stable inhibitor-enzyme complex that requires enzyme resynthesis for recovery
• Competitive displacement of substrate at the active site with immediate recovery
• Induction of enzyme gene expression increasing metabolic capacity over days

Correct Answer: Formation of a stable inhibitor-enzyme complex that requires enzyme resynthesis for recovery

Q2. A reversible competitive inhibitor of CYP3A4 is coadministered with an oral substrate. Which PK change is most likely for the substrate?

• Decrease in absorption rate constant (Ka) with unchanged clearance
• Increase in volume of distribution (Vd) with unchanged clearance
• Increase in apparent oral clearance (CL/F)
• Increase in systemic exposure (AUC) due to reduced metabolic clearance

Correct Answer: Increase in systemic exposure (AUC) due to reduced metabolic clearance

Q3. In a two-compartment IV bolus model, which parameter primarily determines the initial rapid decline phase?

• Peripheral compartment volume (V2)
• Intercompartmental clearance (Q) and distribution into peripheral compartment
• Elimination clearance (CL) from the central compartment only
• Bioavailability (F)

Correct Answer: Intercompartmental clearance (Q) and distribution into peripheral compartment

Q4. In Michaelis–Menten (nonlinear) elimination, which statement is true when Css approaches Km at typical dosing?

• Clearance becomes constant and independent of concentration
• Elimination rate is first-order and directly proportional to concentration
• Small increases in dose produce less-than-proportional increases in AUC
• Elimination rate begins to saturate and AUC increases more than proportionally with dose

Correct Answer: Elimination rate begins to saturate and AUC increases more than proportionally with dose

Q5. Which PK/PD index best correlates with efficacy for time-dependent beta-lactam antibiotics?

• Peak concentration to MIC ratio (Cmax/MIC)
• Area under the concentration–time curve to MIC ratio (AUC/MIC)
• Time that free drug concentration remains above MIC (fT>MIC)
• Time to maximum concentration (Tmax)

Correct Answer: Time that free drug concentration remains above MIC (fT>MIC)

Q6. In population (NLME) modelling, which component accounts for systematic differences between subjects explained by covariates?

• Interindividual variability (IIV) after including covariates
• Random residual unexplained variability (RUV)
• Fixed effects (typical population parameter values and covariate relationships)
• Between-occasion variability (BOV)

Correct Answer: Fixed effects (typical population parameter values and covariate relationships)

Q7. Which parameter is estimated directly in a noncompartmental analysis (NCA) using trapezoidal AUC and terminal slope?

• Intercompartmental clearance (Q)
• Terminal elimination half-life (t1/2)
• Absorption rate constant (Ka) in extravascular dosing
• Central compartment volume (V1)

Correct Answer: Terminal elimination half-life (t1/2)

Q8. A drug is a substrate for P-glycoprotein (P-gp) in the gut. Co-administration of a P-gp inhibitor would most likely cause which effect?

• Decrease in oral bioavailability due to increased efflux
• Increase in oral bioavailability due to reduced efflux from enterocytes
• Increase in renal clearance by enhanced tubular secretion
• Decrease in plasma protein binding

Correct Answer: Increase in oral bioavailability due to reduced efflux from enterocytes

Q9. Which modeling approach is most appropriate to describe target-mediated drug disposition (TMDD) for a high-affinity monoclonal antibody?

• Linear one-compartment model with first-order elimination
• Michaelis–Menten empiric model without target binding terms
• Mechanistic TMDD model incorporating target binding, internalization, and nonlinear clearance
• Noncompartmental analysis using trapezoidal AUC only

Correct Answer: Mechanistic TMDD model incorporating target binding, internalization, and nonlinear clearance

Q10. In enzyme induction mediated by a nuclear receptor, which kinetic characteristic is typical?

• Immediate increase in enzyme activity within minutes of exposure
• Slow onset over days and gradual return to baseline after inducer withdrawal
• Irreversible inhibition of enzyme catalytic site
• Direct competitive inhibition reversible with high substrate concentration

Correct Answer: Slow onset over days and gradual return to baseline after inducer withdrawal

Q11. In concentration–response (Emax) modeling, increasing the Hill coefficient (gamma) primarily affects which characteristic of the curve?

• Maximum effect achievable (Emax)
• Potency (EC50) but not slope
• Slope (steepness) of the concentration–effect relationship around EC50
• Baseline (E0) response

Correct Answer: Slope (steepness) of the concentration–effect relationship around EC50

Q12. A perpetrator drug causes time-dependent inhibition of CYP2D6 via metabolite intermediate complex formation. Which parameter is most useful to quantify potency of this mechanism-based inhibition?

• Ki (reversible inhibition constant)
• kinact and KI (inactivation rate constant and concentration for half-max inactivation)
• EC50 for pharmacodynamic effect
• Volume of distribution at steady state (Vss)

Correct Answer: kinact and KI (inactivation rate constant and concentration for half-max inactivation)

Q13. For an orally dosed drug with significant first-pass hepatic extraction, inhibition of hepatic metabolism will most likely change which parameters?

• Increase oral bioavailability (F) and increase systemic exposure (AUC)
• Decrease central volume of distribution (V1)
• Alter absorption rate constant (Ka) without affecting AUC
• Reduce renal clearance but not hepatic clearance

Correct Answer: Increase oral bioavailability (F) and increase systemic exposure (AUC)

Q14. In PK model evaluation, which diagnostic is most informative for assessing predictive performance across the studied population?

• Conditional weighted residuals (CWRES) vs time plots only
• Visual predictive check (VPC) or prediction-corrected VPC to compare simulated percentiles with observed data
• Simple observation versus individual prediction scatter without variability bands
• Parameter standard errors alone

Correct Answer: Visual predictive check (VPC) or prediction-corrected VPC to compare simulated percentiles with observed data

Q15. Which PK/PD index is most predictive of efficacy for concentration-dependent antibiotics like aminoglycosides?

• Time above MIC (T>MIC)
• AUC/MIC
• Cmax/MIC
• Trough concentration only

Correct Answer: Cmax/MIC

Q16. In a drug–drug interaction where one drug displaces another from plasma proteins, which statement is correct for a low-extraction drug with unchanged clearance?

• Total plasma concentration decreases but free concentration increases significantly
• Free (unbound) concentration transiently increases but clearance of free drug may increase, restoring free concentration to baseline
• Volume of distribution becomes negligible
• Hepatic intrinsic clearance is always reduced

Correct Answer: Free (unbound) concentration transiently increases but clearance of free drug may increase, restoring free concentration to baseline

Q17. Which experimental approach best differentiates between competitive and noncompetitive inhibition in vitro?

• Measuring time to enzyme resynthesis only
• Lineweaver–Burk or Michaelis–Menten plots to assess changes in Km and Vmax
• Measuring urinary excretion over 24 hours
• Comparing AUC after oral and IV dosing without inhibitor

Correct Answer: Lineweaver–Burk or Michaelis–Menten plots to assess changes in Km and Vmax

Q18. In nonlinear mixed-effects modeling, which method is commonly used to assess parameter uncertainty when the likelihood is complex or non-normal?

• Using only asymptotic standard errors from the Fisher information matrix
• Bootstrap resampling to obtain empirical confidence intervals
• Ignoring uncertainty and reporting point estimates
• Calculating simple standard deviation of observations

Correct Answer: Bootstrap resampling to obtain empirical confidence intervals

Q19. Which phenomenon explains increased systemic exposure when two drugs compete for the same hepatic uptake transporter?

• Reduced renal filtration leading to increased plasma protein binding
• Inhibition of hepatic uptake reduces intracellular metabolism, decreasing hepatic clearance and increasing systemic exposure
• Induction of transporter expression increasing clearance
• Increased first-pass metabolism due to transporter competition

Correct Answer: Inhibition of hepatic uptake reduces intracellular metabolism, decreasing hepatic clearance and increasing systemic exposure

Q20. When designing a PK/PD study to estimate EC50 and Emax precisely, which design principle is most important?

• Collect samples only at a single high concentration
• Include a wide range of concentrations that span below and above the expected EC50
• Measure only baseline and one post-dose time point
• Use extremely sparse sampling with many subjects and no concentration variability

Correct Answer: Include a wide range of concentrations that span below and above the expected EC50

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