Therapeutic drug monitoring (TDM) is essential in optimizing pharmacotherapy by measuring drug concentrations and adjusting doses to achieve a safe and effective response. For B.Pharm students, understanding factors influencing TDM—such as pharmacokinetics, sampling time, renal and hepatic function, protein binding, drug interactions, genetic polymorphisms, and assay variability—is critical for rational dose adjustment. Practical considerations include free versus total drug measurement, steady‑state timing, stability and sample handling, and special populations like pediatrics, geriatrics, and pregnancy. Mastery of these concepts enables better interpretation of results for drugs with narrow therapeutic windows (e.g., phenytoin, lithium, digoxin, vancomycin). Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which factor most directly determines the timing of sampling for therapeutic drug monitoring?
- Therapeutic index of the drug
- Patient age
- Pharmacokinetic half‑life of the drug
- Analytical assay sensitivity
Correct Answer: Pharmacokinetic half‑life of the drug
Q2. For drugs that bind extensively to plasma proteins, which measurement gives the most clinically relevant information in hypoalbuminemia?
- Total plasma concentration
- Unbound (free) drug concentration
- Urinary drug concentration
- Salivary drug level
Correct Answer: Unbound (free) drug concentration
Q3. Which process most reduces drug concentration during extracorporeal dialysis?
- Hepatic metabolism
- Increased protein binding
- Drug removal across dialysis membrane
- Enhanced renal tubular reabsorption
Correct Answer: Drug removal across dialysis membrane
Q4. Which pharmacokinetic parameter is directly proportional to dose and inversely proportional to plasma concentration at steady state?
- Volume of distribution (Vd)
- Clearance (Cl)
- Bioavailability (F)
- Half‑life (t1/2)
Correct Answer: Clearance (Cl)
Q5. Which of the following drugs is classically monitored using TDM because of a narrow therapeutic window and variable kinetics?
- Amoxicillin
- Digoxin
- Paracetamol
- Metformin
Correct Answer: Digoxin
Q6. A potent CYP3A4 inducer will most likely cause which change in a CYP3A4‑metabolized drug’s plasma concentration?
- Increase due to inhibited metabolism
- Decrease due to increased metabolism
- No change in concentration
- Increase due to decreased clearance
Correct Answer: Decrease due to increased metabolism
Q7. Why is trough sampling commonly used for aminoglycoside monitoring?
- Trough levels reflect peak efficacy
- Trough levels correlate with toxicity risk and clearance
- It is easier to measure at night
- Peak levels are irrelevant for aminoglycosides
Correct Answer: Trough levels correlate with toxicity risk and clearance
Q8. Which genetic factor most commonly affects warfarin dosing and TDM interpretation?
- CYP2D6 polymorphism
- CYP2C9 and VKORC1 polymorphisms
- UGT1A1 polymorphism
- SLCO1B1 polymorphism
Correct Answer: CYP2C9 and VKORC1 polymorphisms
Q9. For a drug with a large volume of distribution, what is true about plasma concentrations after a single dose?
- Plasma concentration will be high and sustained
- Plasma concentration will be low due to tissue distribution
- Drug will be mostly eliminated renally
- Volume of distribution does not affect plasma concentration
Correct Answer: Plasma concentration will be low due to tissue distribution
Q10. Which sample handling issue can falsely lower measured drug concentration?
- Immediate centrifugation and freezing
- Delayed processing with high room temperature
- Using EDTA tubes for stable drugs
- Transport on ice for temperature‑sensitive drugs
Correct Answer: Delayed processing with high room temperature
Q11. When is it most appropriate to measure a drug level to assess peak concentration for an oral dose?
- Immediately before administration
- At expected Tmax after dosing
- 24 hours after dosing irrespective of half‑life
- During the elimination phase only
Correct Answer: At expected Tmax after dosing
Q12. In chronic renal failure, which adjustment improves TDM interpretation for renally cleared drugs?
- Ignore renal function and use standard ranges
- Estimate creatinine clearance and adjust dosing/targets
- Rely solely on patient symptoms
- Measure only urine drug levels
Correct Answer: Estimate creatinine clearance and adjust dosing/targets
Q13. Which factor can cause assay interference leading to falsely elevated drug levels?
- Cross‑reacting metabolites in immunoassays
- Proper calibration of the assay
- Use of mass spectrometry
- Low hemolysis in samples
Correct Answer: Cross‑reacting metabolites in immunoassays
Q14. For highly protein‑bound drugs, acute hypoalbuminemia typically results in:
- Decreased unbound concentration and decreased effect
- Increased free fraction and potential toxicity despite normal total level
- No change in free fraction
- Lower renal clearance of unbound drug
Correct Answer: Increased free fraction and potential toxicity despite normal total level
Q15. Which parameter indicates that steady state has been reached for a continuously dosed drug?
- Time equal to one half‑life
- Plasma concentrations fluctuate but mean concentration is stable after ~4–5 half‑lives
- Immediate after first dose
- Only after dose doubling
Correct Answer: Plasma concentrations fluctuate but mean concentration is stable after ~4–5 half‑lives
Q16. Which monitoring strategy is most appropriate for phenytoin in a patient with low albumin?
- Measure total phenytoin only
- Measure free phenytoin or correct total concentration for albumin
- Measure urine phenytoin instead of plasma
- No monitoring required
Correct Answer: Measure free phenytoin or correct total concentration for albumin
Q17. Which drug characteristic makes it less likely to be removed by hemodialysis?
- Low protein binding and small molecular weight
- High water solubility and low Vd
- High volume of distribution and high protein binding
- Low lipophilicity
Correct Answer: High volume of distribution and high protein binding
Q18. Which clinical factor commonly necessitates more frequent TDM?
- Stable renal and hepatic function
- Concomitant initiation of interacting drugs
- Long duration of therapy with no changes
- Use of non‑narrow therapeutic index drugs
Correct Answer: Concomitant initiation of interacting drugs
Q19. Why might trough concentrations for vancomycin be a less optimal surrogate than AUC:MIC?
- Troughs are easier to calculate than AUC
- Troughs always perfectly predict efficacy
- AUC:MIC better correlates with efficacy and toxicity than trough alone
- Troughs are not measurable
Correct Answer: AUC:MIC better correlates with efficacy and toxicity than trough alone
Q20. Which preanalytic factor can cause falsely elevated lithium levels?
- Patient fasting before sample
- Use of lithium‑heparin tube for blood collection
- Hemolysis of sample
- Delayed centrifugation at cold temperature
Correct Answer: Hemolysis of sample
Q21. Which statement best describes impact of age on pharmacokinetics relevant to TDM?
- Elderly have increased renal clearance compared to young adults
- Neonates and elderly often have reduced clearance and altered Vd requiring dose adjustments
- Age has no effect on drug levels
- Pediatric patients always require lower mg/kg doses for all drugs
Correct Answer: Neonates and elderly often have reduced clearance and altered Vd requiring dose adjustments
Q22. What is the main reason free drug monitoring may be preferred for highly protein‑bound antimicrobials?
- Total drug level always reflects activity
- Free drug is pharmacologically active and better predicts efficacy/toxicity
- Free drug assays are cheaper and faster
- Protein binding does not change in disease states
Correct Answer: Free drug is pharmacologically active and better predicts efficacy/toxicity
Q23. Which environmental factor can alter oral drug bioavailability and affect TDM interpretation?
- Food intake delaying absorption
- Ambient humidity during storage
- Patient weight only
- Room lighting during sampling
Correct Answer: Food intake delaying absorption
Q24. For a drug with first‑order kinetics, how does clearance change with increasing dose?
- Clearance remains constant regardless of dose
- Clearance increases exponentially with dose
- Clearance decreases as dose increases
- Clearance becomes unpredictable at higher doses
Correct Answer: Clearance remains constant regardless of dose
Q25. Which monitoring consideration is crucial for drugs metabolized by polymorphic enzymes like CYP2C9?
- Genotype has no clinical relevance
- Consider genotyping or closer monitoring because of variable metabolism
- Only measure urinary metabolites
- Use fixed dosing without monitoring
Correct Answer: Consider genotyping or closer monitoring because of variable metabolism
Q26. What effect does acute inflammation (e.g., sepsis) commonly have on drug protein binding?
- Increases albumin leading to increased binding
- Decreases albumin and increases free fraction of highly bound drugs
- No effect on protein binding
- Causes irreversible drug binding to fibrinogen
Correct Answer: Decreases albumin and increases free fraction of highly bound drugs
Q27. Which is the best rationale for therapeutic drug monitoring of antiepileptics like carbamazepine?
- Carbamazepine has no drug‑drug interactions
- It has predictable kinetics in all patients
- Variable metabolism, autoinduction, and narrow therapeutic range justify TDM
- TDM is only needed for antibiotics
Correct Answer: Variable metabolism, autoinduction, and narrow therapeutic range justify TDM
Q28. Which factor most complicates interpretation of single drug level measurements?
- Consistent dosing schedule
- Uncertain sampling time relative to last dose
- Use of validated assay methods
- Stable organ function
Correct Answer: Uncertain sampling time relative to last dose
Q29. In pregnancy, which pharmacokinetic change commonly affects drug concentrations and TDM?
- Decreased renal blood flow and clearance
- Increased plasma albumin increasing protein binding
- Increased volume of distribution and increased renal clearance can lower plasma concentrations
- No physiologic changes impact drug levels
Correct Answer: Increased volume of distribution and increased renal clearance can lower plasma concentrations
Q30. Which is the most appropriate action when TDM shows a drug level within the therapeutic range but the patient has toxicity symptoms?
- Ignore symptoms since level is therapeutic
- Assess free drug level, consider metabolites, drug interactions, and clinical context
- Immediately discontinue all medications
- Repeat the same dose without changes
Correct Answer: Assess free drug level, consider metabolites, drug interactions, and clinical context
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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