PSA PSA Therapeutic Drug Monitoring 1 — Questions and Answers
Question 1: Which of the following drugs requires routine therapeutic drug monitoring (TDM) due to its narrow therapeutic index?
- Amoxicillin
- Vancomycin (Correct answer)
- Azithromycin
- Metformin
Correct answer: Vancomycin
Vancomycin has a narrow therapeutic index and requires routine TDM to ensure efficacy and prevent nephrotoxicity.
Question 2: A patient on digoxin has a serum level of 2.8 ng/mL. The therapeutic range is 0.5–2.0 ng/mL. What is the most appropriate next step?
- Increase the digoxin dose
- Hold digoxin and reassess (Correct answer)
- Continue the current dose
- Switch to a different cardiac glycoside
Correct answer: Hold digoxin and reassess
A digoxin level above the therapeutic range indicates toxicity risk; the dose should be held and the patient reassessed for signs of toxicity.
Question 3: When should a trough level for vancomycin be drawn to accurately reflect steady-state concentrations?
- 30 minutes after the infusion ends
- Immediately before the next dose (Correct answer)
- 2 hours after the infusion starts
- At any random time during therapy
Correct answer: Immediately before the next dose
Vancomycin trough levels should be drawn immediately before the next scheduled dose to reflect the lowest steady-state concentration.
Question 4: Which pharmacokinetic parameter is most important when interpreting TDM results for aminoglycosides?
- Half-life only
- Peak and trough levels (Correct answer)
- Volume of distribution only
- Protein binding percentage
Correct answer: Peak and trough levels
For aminoglycosides, both peak (efficacy) and trough (toxicity avoidance) levels are monitored to optimize dosing.
Question 5: A patient on phenytoin has a total level of 8 mcg/mL (therapeutic 10–20 mcg/mL) but appears clinically stable. Their albumin is 2.0 g/dL. What should you consider?
- Increase phenytoin dose immediately
- Check free phenytoin level before adjusting (Correct answer)
- Discontinue phenytoin
- Switch to levetiracetam without further testing
Correct answer: Check free phenytoin level before adjusting
Phenytoin is highly protein-bound; low albumin increases the free fraction, so a corrected or free phenytoin level is needed before adjusting the dose.
Question 6: Which of the following is the primary reason for performing TDM for lithium?
- Lithium has poor oral bioavailability
- Lithium toxicity can be life-threatening and its therapeutic window is narrow (Correct answer)
- Lithium is rapidly metabolized by the liver
- Lithium causes severe allergic reactions
Correct answer: Lithium toxicity can be life-threatening and its therapeutic window is narrow
Lithium has a narrow therapeutic index and toxicity—manifesting as tremors, confusion, and cardiac arrhythmias—can be severe, making TDM essential.
PSA PSA Therapeutic Drug Monitoring 1
Which of the following drugs requires routine therapeutic drug monitoring (TDM) due to its narrow therapeutic index?