Indications and protocol for TDM MCQs With Answer

Introduction

Therapeutic drug monitoring (TDM) is an essential clinical pharmacokinetic tool used to optimize drug therapy by measuring drug concentrations in biological fluids and adjusting doses to achieve therapeutic outcomes while minimizing toxicity. For M.Pharm students, mastering indications and protocols for TDM is crucial—covering when to monitor, ideal sampling times, analytical and preanalytical considerations, interpretation of levels in special populations, and integration of pharmacokinetic parameters into dosing decisions. This quiz set focuses on depth: clinical indications, sampling timing (peak/trough/AUC), steady-state concepts, assay limitations, and case-based decision triggers. These MCQs are aimed to reinforce applied knowledge for research, hospital pharmacy, and clinical practice.

Q1. Which of the following is the most appropriate primary indication for initiating therapeutic drug monitoring (TDM)?

• Routine monitoring of all antibiotics irrespective of toxicity
• Drugs with a narrow therapeutic index and high pharmacokinetic variability
• Drugs that are always safe and have predictable dose–response
• Monitoring only to document patient adherence without changing therapy

Correct Answer: Drugs with a narrow therapeutic index and high pharmacokinetic variability

Q2. For a drug predominantly cleared by the kidney and having a long half-life in chronic kidney disease, which timing strategy is most critical for TDM to guide dose adjustment?

• Random sampling at any clinic visit
• Peak level 1 hour post-dose only
• Trough concentration at steady state before the next dose
• Multiple hourly samples for 24 hours every week

Correct Answer: Trough concentration at steady state before the next dose

Q3. When measuring the peak concentration for an aminoglycoside to assess efficacy, the recommended sampling time after an intravenous bolus dose is approximately:

• Immediately before the next dose
• 30 minutes after the end of infusion (or 30–60 min after bolus)
• 12 hours post-dose
• At steady state without relation to dose timing

Correct Answer: 30 minutes after the end of infusion (or 30–60 min after bolus)

Q4. Which pharmacokinetic parameter is best estimated when performing multiple timed samples to calculate area under the concentration–time curve (AUC) for vancomycin?

• Apparent volume of distribution only
• Clearance, which relates dose to AUC (AUC = Dose/Cl)
• Bioavailability in oral dosing exclusively
• Protein binding percentage

Correct Answer: Clearance, which relates dose to AUC (AUC = Dose/Cl)

Q5. For a patient on phenytoin with hypoalbuminemia, which adjustment or interpretation consideration is most appropriate when interpreting total phenytoin concentration?

• Report unadjusted total concentration; no further action
• Use corrected (adjusted) phenytoin concentration or measure free phenytoin
• Assume lower toxicity risk due to low albumin
• Increase dose based solely on total concentration

Correct Answer: Use corrected (adjusted) phenytoin concentration or measure free phenytoin

Q6. Which preanalytical factor is most likely to cause falsely low drug concentration in a TDM sample?

• Collecting sample at true trough time
• Inappropriate sample handling with delayed centrifugation and storage at room temperature
• Using the correct anticoagulant and promptly freezing plasma
• Sampling during steady state with correct timing

Correct Answer: Inappropriate sample handling with delayed centrifugation and storage at room temperature

Q7. Which of the following drugs is least commonly monitored by routine TDM in clinical practice?

• Vancomycin
• Digoxin
• Warfarin
• Metformin

Correct Answer: Metformin

Q8. In a one-compartment model, steady state is generally achieved after approximately how many half-lives of the drug?

• About 1 half-life
• Approximately 3–4 half-lives
• Approximately 4–5 half-lives
• More than 10 half-lives

Correct Answer: Approximately 4–5 half-lives

Q9. When should trough sampling be scheduled for an outpatient receiving oral theophylline twice daily for TDM?

• 2 hours after taking the dose
• Immediately before the morning dose (just prior to dosing)
• Randomly at lunchtime
• Immediately after breakfast regardless of dose timing

Correct Answer: Immediately before the morning dose (just prior to dosing)

Q10. In interpreting TDM results, which situation most strongly suggests a compliance problem rather than altered pharmacokinetics?

• Unexpectedly low trough followed by subtherapeutic AUC with documented dosing times inconsistent with sampling
• Elevated trough with concomitant renal failure
• High peak after appropriate dosing with normal clearance
• Stable levels with no change in clinical effect

Correct Answer: Unexpectedly low trough followed by subtherapeutic AUC with documented dosing times inconsistent with sampling

Q11. Which assay characteristic is most critical for reliable TDM decision-making when drug concentrations are close to the therapeutic threshold?

• High limit of detection only
• High analytical precision and low bias at the clinical decision range
• Long run time per sample with complex extraction
• Ability to test multiple drugs at once irrespective of accuracy

Correct Answer: High analytical precision and low bias at the clinical decision range

Q12. A clinician wants to personalize tacrolimus dosing in a renal transplant patient. Which TDM approach provides the most informative assessment to optimize dose with respect to drug exposure and nephrotoxicity risk?

• Single random concentration drawn without relation to dosing
• Pre-dose trough concentrations and, when needed, limited AUC sampling or population PK modeling
• Only measuring trough levels on day 1 post-transplant
• Monitoring liver enzymes instead of drug levels

Correct Answer: Pre-dose trough concentrations and, when needed, limited AUC sampling or population PK modeling

Q13. For drugs that exhibit non-linear (capacity-limited) kinetics such as phenytoin, which statement about dose–concentration relationship is accurate?

• Plasma concentration increases proportionally with dose across all ranges
• Small dose changes may produce disproportionate concentration changes due to saturable metabolism
• Clearance remains constant regardless of concentration
• Monitoring is unnecessary because kinetics are predictable

Correct Answer: Small dose changes may produce disproportionate concentration changes due to saturable metabolism

Q14. Which population is most likely to require more frequent TDM due to rapidly changing pharmacokinetics?

• Stable outpatient with normal renal function
• Critically ill ICU patient with fluctuating organ function and multiple drugs
• Young healthy volunteer in a single-dose study
• Patient on long-term stable monotherapy with no comorbidities

Correct Answer: Critically ill ICU patient with fluctuating organ function and multiple drugs

Q15. When should free (unbound) drug concentration measurement be preferred over total concentration in TDM?

• When the drug is minimally protein bound
• When alterations in protein binding (e.g., hypoalbuminemia) are present and free fraction changes impact pharmacologic effect
• When only total concentration correlates with toxicity
• When measuring oral bioavailability

Correct Answer: When alterations in protein binding (e.g., hypoalbuminemia) are present and free fraction changes impact pharmacologic effect

Q16. Which is a valid reason to perform trough-only monitoring instead of full AUC estimation for a drug like vancomycin in routine practice?

• Trough correlates poorly with exposure and always misleads dosing
• Resource limitations and validated trough-target strategies that approximate exposure for many patients
• Trough sampling eliminates need for clinical correlation
• Trough-only monitoring gives exact AUC values

Correct Answer: Resource limitations and validated trough-target strategies that approximate exposure for many patients

Q17. A patient on lithium presents with signs of toxicity. Which immediate TDM action is most appropriate?

• Obtain a random lithium level at any time
• Obtain a trough lithium concentration 12 hours after the last dose and correlate with clinical status and renal function
• Wait 5 days to allow levels to equilibrate
• Measure only urine lithium concentration

Correct Answer: Obtain a trough lithium concentration 12 hours after the last dose and correlate with clinical status and renal function

Q18. Which of the following best describes “reactive” versus “routine” TDM?

• “Reactive” TDM is scheduled at fixed intervals, “routine” TDM is done only for toxicity
• “Reactive” TDM is performed in response to clinical problems (toxicity or treatment failure); “routine” TDM is scheduled as part of regular monitoring
• Both terms are synonymous
• “Routine” TDM is only used in research settings while “reactive” is clinical

Correct Answer: “Reactive” TDM is performed in response to clinical problems (toxicity or treatment failure); “routine” TDM is scheduled as part of regular monitoring

Q19. Which drug–drug interaction scenario would most likely necessitate increased frequency of TDM?

• Co-administration of two drugs with entirely separate elimination pathways and no PK interaction
• Initiation of a strong CYP3A4 inhibitor in a patient stabilized on tacrolimus
• Administration of vitamin supplements with no known interactions
• Switching from oral to parenteral formulation with identical clearance

Correct Answer: Initiation of a strong CYP3A4 inhibitor in a patient stabilized on tacrolimus

Q20. Which documentation is essential for reliable interpretation of a TDM result?

• Only the laboratory assay used, nothing about dosing or timing
• Exact dose, time of last dose, sampling time relative to dose, formulation, renal/hepatic function, and co-medications
• Poorly recorded dosing history and uncertain sampling time
• Only patient age and gender without clinical context

Correct Answer: Exact dose, time of last dose, sampling time relative to dose, formulation, renal/hepatic function, and co-medications

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