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
