PSA PSA Therapeutic Drug Monitoring 2 — Questions and Answers
Question 1: A patient on theophylline for COPD has a level of 22 mcg/mL (therapeutic 10–20 mcg/mL). Which symptom is most consistent with theophylline toxicity?
- Bradycardia
- Seizures (Correct answer)
- Hypotension
- Hypoglycemia
Correct answer: Seizures
Theophylline toxicity can cause seizures, tachycardia, and arrhythmias, with seizures being a serious manifestation at supratherapeutic levels.
Question 2: Which condition would most likely increase cyclosporine blood levels and require downward dose adjustment?
- Co-administration of rifampin
- Co-administration of fluconazole (Correct answer)
- High-fiber diet
- Increased physical activity
Correct answer: Co-administration of fluconazole
Fluconazole inhibits CYP3A4, reducing cyclosporine metabolism and increasing blood levels, necessitating dose reduction.
Question 3: For patients on warfarin, INR is used as a surrogate for TDM. A patient with atrial fibrillation has an INR of 4.8 (target 2.0–3.0). What is the most appropriate action if there is no active bleeding?
- Give IV vitamin K 10 mg
- Hold warfarin and recheck INR in 1–2 days (Correct answer)
- Give fresh frozen plasma immediately
- Increase warfarin dose
Correct answer: Hold warfarin and recheck INR in 1–2 days
For a supratherapeutic INR without active bleeding, holding warfarin and rechecking in 1–2 days is the standard approach.
Question 4: Which of the following best describes why TDM for tacrolimus uses whole blood rather than serum?
- Tacrolimus is unstable in serum at room temperature
- Tacrolimus concentrates extensively in red blood cells (Correct answer)
- Serum processing destroys tacrolimus
- Tacrolimus is not detectable in serum
Correct answer: Tacrolimus concentrates extensively in red blood cells
Tacrolimus binds extensively to erythrocytes, making whole blood the appropriate matrix for accurate TDM.
Question 5: A patient on methotrexate for rheumatoid arthritis has elevated liver enzymes. What monitoring parameter is specifically recommended to prevent methotrexate hepatotoxicity?
- Regular serum methotrexate levels
- Liver function tests and CBC at regular intervals (Correct answer)
- Daily urine drug screens
- Monthly echocardiograms
Correct answer: Liver function tests and CBC at regular intervals
Regular liver function tests and CBC are recommended for patients on methotrexate to detect hepatotoxicity and myelosuppression early.
Question 6: When interpreting a gentamicin peak level drawn 30 minutes after a 30-minute infusion ends, the result is 14 mcg/mL (therapeutic peak 5–10 mcg/mL for traditional dosing). What is the most appropriate action?
- Continue the same dose
- Extend the dosing interval (Correct answer)
- Reduce the dose and shorten the interval
- Discontinue gentamicin immediately
Correct answer: Extend the dosing interval
A supratherapeutic peak with traditional aminoglycoside dosing warrants extending the dosing interval to allow adequate drug elimination and prevent toxicity.
PSA PSA Therapeutic Drug Monitoring 2
A patient on theophylline for COPD has a level of 22 mcg/mL (therapeutic 10–20 mcg/mL).
Which symptom is most consistent with theophylline toxicity?