Introduction: Therapeutic Drug Monitoring (TDM) is a clinical tool used to measure drug concentrations in biological matrices to optimize dosing, improve efficacy, and minimize toxicity. For B.Pharm students, understanding TDM involves pharmacokinetics, therapeutic window, steady-state, peak and trough sampling, assay selection, and interpretation of results. TDM’s purpose and significance include dose individualization for drugs with narrow therapeutic indices, large interpatient variability, or important concentration–response relationships. Knowledge of pre-analytical factors, protein binding, clearance, volume of distribution, and pharmacogenomics is essential for correct clinical decisions. This concise, keyword-rich overview prepares you to apply TDM principles in practice. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary purpose of Therapeutic Drug Monitoring (TDM)?
- To determine drug purity in manufacturing
- To measure blood drug concentrations to guide dosage adjustments
- To monitor patient adherence only through questionnaires
- To replace clinical assessment of drug effect
Correct Answer: To measure blood drug concentrations to guide dosage adjustments
Q2. Which characteristic most strongly indicates a drug is a candidate for TDM?
- Wide therapeutic index and predictable response
- Low variability in pharmacokinetics between patients
- Narrow therapeutic index and high interpatient variability
- Primary renal excretion without active metabolites
Correct Answer: Narrow therapeutic index and high interpatient variability
Q3. When is the trough concentration typically sampled for TDM?
- At the time of anticipated maximum concentration (Tmax)
- Immediately after drug administration
- Just before the next scheduled dose
- At random during the dosing interval
Correct Answer: Just before the next scheduled dose
Q4. Why is steady-state important for interpreting TDM results?
- Steady-state ensures drug elimination is complete
- Concentrations at steady-state are independent of dosing history
- Steady-state concentrations reflect the balance between dosing rate and clearance
- Steady-state only matters for single-dose studies
Correct Answer: Steady-state concentrations reflect the balance between dosing rate and clearance
Q5. Which pharmacokinetic parameter most directly affects loading dose calculation?
- Clearance (CL)
- Volume of distribution (Vd)
- Bioavailability (F)
- Half-life (t1/2)
Correct Answer: Volume of distribution (Vd)
Q6. A drug shows high plasma protein binding. How can hypoalbuminemia influence measured total drug concentration?
- Total concentration will decrease and free concentration will proportionally decrease
- Total concentration will increase but free concentration may remain unchanged or increase
- Total concentration is unaffected by plasma proteins
- Free concentration always decreases with hypoalbuminemia
Correct Answer: Total concentration will increase but free concentration may remain unchanged or increase
Q7. Which assay method provides the highest specificity for TDM of complex drugs and metabolites?
- Immunoassay
- High-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS)
- Colorimetric assay
- Thin-layer chromatography (TLC)
Correct Answer: High-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS)
Q8. For a drug with a half-life of 12 hours, approximately how long to reach steady-state with regular dosing?
- About 12 hours
- About 24 hours
- About 48–60 hours (4–5 half-lives)
- About 7–10 days
Correct Answer: About 48–60 hours (4–5 half-lives)
Q9. Which clinical scenario best warrants immediate TDM?
- Routine monitoring of a short-acting analgesic with wide therapeutic index
- Initiating vancomycin in a critically ill patient with fluctuating renal function
- Starting a topical steroid
- Administering a single dose of an antihistamine
Correct Answer: Initiating vancomycin in a critically ill patient with fluctuating renal function
Q10. What is the main limitation of immunoassays in TDM?
- They are always slower than chromatographic methods
- Cross-reactivity with metabolites or structurally similar compounds can cause inaccuracies
- They cannot detect drugs in plasma
- They require mass spectrometers
Correct Answer: Cross-reactivity with metabolites or structurally similar compounds can cause inaccuracies
Q11. How does renal impairment commonly affect drug concentrations monitored by TDM?
- It always lowers both total and free drug concentrations
- It decreases clearance, leading to accumulation and higher concentrations
- It increases hepatic metabolism to compensate
- It has no effect on drug pharmacokinetics
Correct Answer: It decreases clearance, leading to accumulation and higher concentrations
Q12. Which sampling time is most appropriate to assess peak concentration for an IV infusion TDM?
- Immediately before infusion
- At the end of the infusion or shortly after completion
- 24 hours after infusion
- At any random time
Correct Answer: At the end of the infusion or shortly after completion
Q13. In TDM, Bayesian dosing uses which of the following to individualize therapy?
- Only the population mean concentration without patient data
- Population pharmacokinetic models combined with individual patient concentration data
- Randomized clinical trial results without concentrations
- Only genetic testing results
Correct Answer: Population pharmacokinetic models combined with individual patient concentration data
Q14. Which antibiotic traditionally requires TDM due to narrow therapeutic index and nephrotoxicity risk?
- Amoxicillin
- Vancomycin
- Cefazolin
- Azithromycin
Correct Answer: Vancomycin
Q15. What pre-analytical factor can falsely lower measured drug concentration?
- Prompt centrifugation and freezing
- Delayed sample processing allowing drug degradation
- Using matched anticoagulant tubes as recommended
- Proper labeling and storage at recommended temperature
Correct Answer: Delayed sample processing allowing drug degradation
Q16. Which statement about therapeutic range is correct?
- Therapeutic range is universal for all patients and needs no clinical correlation
- Therapeutic range represents concentrations where most patients have desired effects with acceptable toxicity
- Concentrations below the range are always toxic
- Therapeutic ranges are irrelevant for drugs with narrow therapeutic indices
Correct Answer: Therapeutic range represents concentrations where most patients have desired effects with acceptable toxicity
Q17. How can pharmacogenetic variability influence TDM results?
- Genetic differences do not affect drug metabolism
- They can alter metabolic enzyme activity leading to unexpected concentrations requiring dose adjustment
- They only affect drug absorption, not monitored concentrations
- Pharmacogenetics replaces the need for TDM entirely
Correct Answer: They can alter metabolic enzyme activity leading to unexpected concentrations requiring dose adjustment
Q18. Which parameter is calculated as Dose rate divided by plasma concentration at steady-state?
- Volume of distribution (Vd)
- Clearance (CL)
- Bioavailability (F)
- Half-life (t1/2)
Correct Answer: Clearance (CL)
Q19. Which matrix is most commonly used for routine TDM in clinical practice?
- Urine
- Plasma or serum
- Saliva exclusively
- Tissue biopsy
Correct Answer: Plasma or serum
Q20. What is the impact of drug–drug interactions on TDM interpretation?
- They always decrease monitored drug concentrations
- They can increase or decrease concentrations by altering metabolism, requiring reassessment of therapeutic range
- They have no clinical significance for TDM
- They only affect pharmacodynamics, not concentrations
Correct Answer: They can increase or decrease concentrations by altering metabolism, requiring reassessment of therapeutic range
Q21. For a once-daily oral drug, when is trough sampling typically performed?
- 2 hours after dose
- Just before the next morning dose
- Immediately after the dose
- Exactly at Tmax
Correct Answer: Just before the next morning dose
Q22. Which factor decreases apparent clearance and may necessitate dose reduction?
- Enhanced hepatic enzyme induction
- Renal failure reducing drug elimination
- Increased cardiac output improving perfusion
- Decreased protein binding leading to lower total drug levels
Correct Answer: Renal failure reducing drug elimination
Q23. When interpreting a low total drug concentration for a highly protein-bound drug, what additional measurement can improve interpretation?
- Urine drug level
- Free (unbound) drug concentration
- Only repeating the total concentration without context
- Creatinine clearance only
Correct Answer: Free (unbound) drug concentration
Q24. Which clinical outcome does TDM most directly help to prevent?
- Adverse drug reactions due to supratherapeutic levels
- Medication packaging errors
- Wrong drug selection at prescription
- Patient noncompliance in all cases
Correct Answer: Adverse drug reactions due to supratherapeutic levels
Q25. Which drug is an example where saliva TDM may be useful to measure unbound concentrations?
- Digoxin
- Phenytoin
- Warfarin
- Heparin
Correct Answer: Phenytoin
Q26. What does a single TDM concentration without clinical context risk leading to?
- Perfect dosing decisions in all patients
- Misinterpretation and inappropriate dose changes
- Elimination of the need for clinical assessment
- Immediate therapeutic success
Correct Answer: Misinterpretation and inappropriate dose changes
Q27. How can therapeutic range differ between populations?
- It never varies and is fixed globally
- Differences in age, comorbidities, genetics, and drug interactions can shift optimal ranges
- Only lab methods change the range, not population factors
- Therapeutic range is only dependent on drug cost
Correct Answer: Differences in age, comorbidities, genetics, and drug interactions can shift optimal ranges
Q28. Which is a key advantage of chromatographic methods (e.g., HPLC-MS/MS) over immunoassays for TDM?
- Lower specificity and more cross-reactivity
- Higher specificity and ability to separate parent drug from metabolites
- They require no sample preparation
- They are always less sensitive than immunoassays
Correct Answer: Higher specificity and ability to separate parent drug from metabolites
Q29. What role does clinical pharmacokinetics play in TDM-based dose adjustment?
- None; dosing is based only on standard fixed regimens
- It provides mathematical tools to predict concentration changes and guide individualized dosing
- It replaces laboratory measurements completely
- It is only theoretical and has no bedside application
Correct Answer: It provides mathematical tools to predict concentration changes and guide individualized dosing
Q30. When might repeat TDM sampling be necessary after an initial abnormal result?
- Never; one measurement is always sufficient
- After dose adjustment, change in organ function, or suspected nonadherence to confirm new steady-state
- Only when the drug is discontinued permanently
- Only if the assay method changes
Correct Answer: After dose adjustment, change in organ function, or suspected nonadherence to confirm new steady-state
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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