TDM examples: Digoxin, Lidocaine, Amiodarone MCQs With Answer

TDM examples: Digoxin, Lidocaine, Amiodarone MCQs With Answer — Introduction

Therapeutic drug monitoring (TDM) is essential in optimizing efficacy and minimizing toxicity of narrow therapeutic index antiarrhythmics. This set of MCQs focuses on practical clinical pharmacokinetics and monitoring principles for digoxin, lidocaine and amiodarone — three commonly used agents with distinct pharmacokinetic profiles, interactions and monitoring needs. Questions cover therapeutic ranges, sampling timing, drug interactions, metabolism, toxicity signs, antidotes, effects of organ dysfunction and laboratory assay issues. Designed for M.Pharm students, these items aim to deepen understanding of when and how to apply TDM, interpret levels, and integrate pharmacokinetic reasoning into clinical decision-making for safe and effective therapy.

Q1. Which plasma concentration range is widely recommended for digoxin therapy in patients with heart failure to minimize toxicity while retaining benefit?

• 0.1–0.4 ng/mL
• 0.5–0.9 ng/mL
• 1.5–2.5 ng/mL
• 2.0–3.5 ng/mL

Correct Answer: 0.5–0.9 ng/mL

Q2. For accurate digoxin concentration measurement to avoid the distribution phase artifact after an oral dose, the blood sample should be drawn:

• Immediately after the dose
• 1–2 hours after the dose
• At least 6–8 hours after the dose (preferably trough)
• Only after 30 days of therapy

Correct Answer: At least 6–8 hours after the dose (preferably trough)

Q3. Amiodarone increases serum digoxin concentrations primarily by which mechanism?

• Induction of renal clearance of digoxin
• Inhibition of P-glycoprotein leading to decreased digoxin clearance
• Increasing hepatic metabolism of digoxin
• Enhancing digoxin protein binding

Correct Answer: Inhibition of P-glycoprotein leading to decreased digoxin clearance

Q4. The commonly accepted therapeutic plasma concentration range for lidocaine when used as an antiarrhythmic infusion is approximately:

• 0.1–0.6 µg/mL
• 1.5–5.0 µg/mL
• 10–20 µg/mL
• 25–50 µg/mL

Correct Answer: 1.5–5.0 µg/mL

Q5. The major active metabolite of lidocaine that can contribute to pharmacologic effects and toxicity is:

• Monoethylglycinexylidide (MEGX)
• Desethylamiodarone (DEA)
• Digibind
• Glyceryl trinitrate

Correct Answer: Monoethylglycinexylidide (MEGX)

Q6. Which antiarrhythmic is known to decrease the apparent volume of distribution of digoxin and thereby raise serum digoxin concentrations?

• Quinidine
• Amiodarone
• Propranolol
• Furosemide

Correct Answer: Quinidine

Q7. The elimination half-life of amiodarone is best described as:

• Very short: 1–3 hours
• Moderate: 6–12 hours
• Long: 25–100 days due to tissue accumulation
• Exactly 48 hours in all patients

Correct Answer: Long: 25–100 days due to tissue accumulation

Q8. Which of the following is least useful as routine monitoring during amiodarone therapy?

• Liver function tests (LFTs)
• Thyroid function tests (TFTs)
• Chest radiography or pulmonary assessment
• Frequent plasma amiodarone concentration measurement for dose titration

Correct Answer: Frequent plasma amiodarone concentration measurement for dose titration

Q9. In patients with end-stage renal disease receiving hemodialysis, digoxin is:

• Effectively removed and requires supplemental dosing after dialysis
• Not significantly removed by hemodialysis because of large tissue distribution
• Destroyed by dialysis filters leading to decreased toxicity
• Converted to inactive metabolites during dialysis

Correct Answer: Not significantly removed by hemodialysis because of large tissue distribution

Q10. Hypokalemia affects digoxin therapy by:

• Decreasing digoxin serum concentration without changing toxicity
• Increasing sensitivity of cardiac tissue to digoxin and raising risk of toxicity
• Enhancing digoxin renal clearance
• Binding digoxin to albumin and reducing free drug

Correct Answer: Increasing sensitivity of cardiac tissue to digoxin and raising risk of toxicity

Q11. Which laboratory issue can lead to falsely elevated digoxin concentrations on some immunoassays?

• Presence of digoxin-like immunoreactive substances (DLIS) or cross-reacting endogenous factors
• Low serum potassium
• Hyperglycemia above 200 mg/dL
• Concurrent use of lidocaine infusion

Correct Answer: Presence of digoxin-like immunoreactive substances (DLIS) or cross-reacting endogenous factors

Q12. The primary hepatic metabolite of amiodarone that is also pharmacologically active is:

• Monoethylglycinexylidide (MEGX)
• Desethylamiodarone (DEA)
• Digoxin-specific Fab
• Glycylxylidide (GX)

Correct Answer: Desethylamiodarone (DEA)

Q13. Lidocaine toxicity typically presents first with which clinical features?

• Renal failure and hyperkalemia
• CNS excitatory symptoms such as perioral numbness, tinnitus and seizures
• Severe hypothyroidism
• Thrombocytopenia and anemia

Correct Answer: CNS excitatory symptoms such as perioral numbness, tinnitus and seizures

Q14. When monitoring a continuous lidocaine infusion for ventricular arrhythmia, an appropriate time to obtain a steady‑state plasma concentration is:

• After 10–20 minutes of infusion
• After 6–12 hours of continuous infusion
• Only after 7 days of therapy
• Immediately after stopping the infusion

Correct Answer: After 6–12 hours of continuous infusion

Q15. Co-administration of amiodarone with warfarin commonly requires which adjustment or monitoring?

• No change; amiodarone has no effect on warfarin
• Decreased warfarin dose and closer INR monitoring due to CYP inhibition
• Increased warfarin dose because amiodarone induces warfarin metabolism
• Switch to low molecular weight heparin immediately

Correct Answer: Decreased warfarin dose and closer INR monitoring due to CYP inhibition

Q16. The recommended antidote for life-threatening digoxin toxicity (severe arrhythmias or hyperkalemia) is:

• Activated charcoal only
• Digoxin-specific antibody fragments (Digibind/DigiFab)
• Intravenous lidocaine
• High-dose potassium supplementation

Correct Answer: Digoxin-specific antibody fragments (Digibind/DigiFab)

Q17. Which clinical condition will most prolong lidocaine elimination half-life and increase risk of accumulation?

• Acute gastroenteritis
• Hepatic impairment with reduced metabolic capacity
• Hyperthyroidism
• Use of topical benzocaine

Correct Answer: Hepatic impairment with reduced metabolic capacity

Q18. Amiodarone therapy is most characteristically associated with which thyroid effect?

• Only hypothyroidism due to iodine deficiency
• Only hyperthyroidism due to excess iodine
• Either hypothyroidism or hyperthyroidism (both are possible)
• No effect on thyroid function

Correct Answer: Either hypothyroidism or hyperthyroidism (both are possible)

Q19. Which statement about therapeutic drug monitoring in these three drugs is most accurate?

• Amiodarone plasma concentration tightly correlates with clinical effect and is the primary monitoring tool
• Lidocaine requires no monitoring because it has a wide therapeutic index
• Digoxin has well-established plasma ranges used clinically, while amiodarone plasma levels correlate poorly with effect
• All three drugs are equally amenable to simple routine TDM with rapid steady-state sampling

Correct Answer: Digoxin has well-established plasma ranges used clinically, while amiodarone plasma levels correlate poorly with effect

Q20. Which interaction would most likely raise digoxin plasma concentration and necessitate dose reduction or close monitoring?

• Co-administration of rifampicin (a strong enzyme inducer)
• Co-administration of amiodarone
• Administration of activated charcoal once daily
• Starting an oral laxative regimen

Correct Answer: Co-administration of amiodarone

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