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Difficulty: MediumMonitoring and Treatment Evaluation

A 68-year-old woman with highly symptomatic paroxysmal atrial fibrillation is admitted to the cardiology service for initiation of dofetilide therapy. Her past medical history is significant for hypertension and heart failure with preserved ejection fraction. Her home medications include metoprolol succinate, losartan, and apixaban. Which of the following parameters must be strictly monitored during the initial inpatient phase of therapy with this medication? (Select all that apply)

  1. Continuous electrocardiographyAnswer
  2. Serum creatinineAnswer
  3. Serum potassium and magnesiumAnswer
  4. D
    Thyroid-stimulating hormone (TSH)
  5. E
    Pulmonary function tests

Answer

The correct parameters to monitor are continuous electrocardiography, serum creatinine, and serum potassium and magnesium.
Dofetilide is a potent Class III antiarrhythmic with a narrow therapeutic index and a high risk of causing drug-induced Long QT syndrome and Torsades de Pointes. To mitigate this risk, strict regulatory and clinical protocols mandate that initiation occur in a monitored inpatient setting for at least 72 hours (or 5 doses). During this time, continuous electrocardiography (telemetry) is required to monitor the QT c_c interval after each dose. Because the drug is primarily cleared by the kidneys, serum creatinine must be drawn to calculate creatinine clearance, as dosing is highly dependent on renal function. Furthermore, serum potassium and magnesium must be monitored and aggressively repleted, as hypokalemia and hypomagnesemia independently prolong the QT interval and synergistically increase the risk of fatal arrhythmias.

Step-by-Step Solution

1
Identify the pharmacologic properties of the newly initiated medication.
Dofetilide is a Class III antiarrhythmic agent that prolongs the cardiac action potential and the QT interval by blocking IKrI_{Kr} potassium channels.
Understanding the drug's mechanism highlights its primary adverse effect: dose-dependent QT prolongation leading to Torsades de Pointes.
2
Determine the clearance mechanism of the drug.
Dofetilide is primarily excreted unchanged by the kidneys.
Small fluctuations in renal function can cause drug accumulation and dangerous toxicity, necessitating strict dose adjustments based on creatinine clearance.
3
Apply standard safety guidelines for drug initiation.
Guidelines mandate a 72-hour inpatient admission for continuous ECG telemetry, serial renal function checks (serum creatinine), and electrolyte monitoring (potassium and magnesium).
This highly controlled environment ensures the QT interval remains within safe limits and arrhythmias are immediately treated if they occur.

Key Concept

Initiation of dofetilide requires mandatory inpatient admission for continuous electrocardiographic monitoring, renal function assessment, and electrolyte optimization due to the high risk of life-threatening QT prolongation.
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Topics

Monitoring and Treatment Evaluation

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