NAPLEX Question of the Week: Pacerone Puzzle

A widely used agent is the subject of our question of the week!
NAPLEX Question of the Week: Pacerone Puzzle
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PM is a 39 yo female recently discharged from the hospital who presents to the pharmacy with a new prescription for Pacerone 200 mg orally daily.
 
Current Medication List:
Jantoven 5 mg orally daily
Lipitor 40 mg orally daily
Lisinopril 40 mg orally daily
Metformin 500 mg orally BID
Zoloft 100 mg orally daily
 
PMH: HLD, T2DM, HTN, MDD, Atrial Fibrillation
 
Vitals and Lab Results:
HR: 78 BPM
RR: 18 BPM
Temp: 98.6 F
BP: 127/77 mm Hg
Na: 143 meq/L
ALT: 37 U/L
AST: 33 U/L
SCr: 1.8 mg/dL
K: 4.3 meq/L
BG: 122 mg/dL
TDL: 177 mg/dL
HDL: 37 mg/dL
LDL:122 mg/dL
Triglycerides: 144 mg/dL
 
While you evaluate this patient's new Pacerone prescription, you recall the medication's noticeable toxicities and interactions. Which of the following is true about Pacerone? Select all that apply.
 
A. Pacerone may decrease INR when taken with Jantoven.
B. Pacerone and Zoloft both have a potential risk of QTc prolongation.
C. Pacerone has a boxed warning for pulmonary toxicity and hepatotoxicity.
D. Pacerone would not be expected to be excreted in breastmilk. 
E. Pacerone as prescribed should be reduced to 100mg daily based on Clcr. 
 
Atrial fibrillation is a type of cardiac arrhythmia caused by electrical abnormalities in the atrium of the heart. It often leads to an increased heart rate and may produce symptoms including palpitations or fatigue. An electrocardiogram is used to diagnose atrial fibrillation and treatment strategies include rate control and rhythm control. Because blood is not pumped efficiently through the heart, blood clots may form which can lead to a stroke. CHA2DS2-VASc should be used to assess patient risk of thromboembolic events and aid in the choice to initiate anticoagulation.
 
Pacerone (amiodarone) is a Class III antiarrhythmic that may be used for rate or rhythm control in the treatment of atrial fibrillation. Although this medication is highly effective, it boasts a variety of side effects and drug interactions—a few of which we will discuss below.

Answers with rationale: 
 
Answer choice A is incorrect. Jantoven (Warfarin) is metabolized by CYP 2C9 and Pacerone is a CYP 2C9 inhibitor. Coadministration leads to decreased warfarin metabolism, increased INR levels, and increased bleeding risk. Patient INR should be monitored closely and a dose reduction of warfarin may be considered. 
 
Answer choice B is correct. Both Pacerone and Zoloft (sertraline) are QTc-prolonging agents and concomitant use may enhance their QTc-prolonging effects and subsequent risk of developing a dangerous arrhythmia known as Torsades de Pointes. When evaluating the risk of concomitant use, take into account other factors that may increase a patient’s risk for developing Torsades, such as older age, sex, electrolyte abnormalities (e.g. hypokalemia).
 
Answer choice C is correct. Pacerone can cause fatal pulmonary toxicity and hepatotoxicity. Patients should receive a baseline pulmonary function test and liver function test before treatment with follow up monitoring after initiating Pacerone. Consider alternative therapy if patient develops signs or symptoms of pulmonary toxicity or hepatotoxicity.
 
Answer choice D is incorrect. A relative infant dose (RID) of <10% is generally acceptable for medication use. Pacerone and one of its metabolites have a reported RID between 3.5% and 45% so in general amiodarone should be avoided in breastfeeding patients. A significant amount of iodine is provided by this medication which could affect the infant, even upon discontinuation, as the long half-life of the medication allows it to persist long after it is no longer being administered. 
 
Answer choice E is incorrect. Pacerone is known to decrease heart rate. This allows it to be useful for rate control in some patients, but it can cause unwanted symptomatic bradycardia in others. Monitor patient heart rate and watch for symptoms such as fatigue and syncope.

Medications: Pacerone (Amiodarone), Jantoven (Warfarin), Lipitor (Atorvastatin), Prinivil (Lisinopril), Glucophage (Metformin), Zoloft (Sertraline)
 
Competencies:
Area 2 - Identify Drug Characteristics
2.2 - Commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names; physical descriptions; or how supplied
2.3 - Boxed warnings or REMS
2.4 - Pregnancy or lactation
Area 3 - Develop or Manage Treatment Plans
3.7 - Adverse drug effects, toxicology, or overdose
3.8 - Drug Interactions

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