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Class III Antidysrhythmic Drugs – NCLEX-Style
Questions on Potassium Channel Blockers (Amiodarone,
Sotalol, Dofetilide) with Answers & Rationales | A-Graded
Pharmacology Exam Prep
Class III antidysrhythmics, also known ✔✔✔answer✔✔✔as potassium channel blockers,
prolong the repolarization period, which prolongs the QT interval (the length of time it takes for the ventricles to depolarize and completely repolarize). These drugs are not a first-line treatment and are only prescribed when the patient has a life-threatening ventricular tachycardia or fibrillation. The various Class III antidysrhythmics are not interchangeable, as they have varying secondary effects. There are currently five Class III antidysrhythmic drugs available:
✔✔✔answer✔✔✔amiodarone, dronedarone, ibutilide, dofetilide, and sotalol (which is
also a beta blocker). This lesson will discuss amiodarone and dronedarone.
Amiodarone absorption ✔✔✔answer✔✔✔Absorbed by fat
Amiodarone distribution ✔✔✔answer✔✔✔Extensively bound to protein (more than 99%)
Amiodarone metabolism ✔✔✔answer✔✔✔Liver
Amiodarone excretion ✔✔✔answer✔✔✔Feces and urine
Dronedarone absorption ✔✔✔answer✔✔✔absorption is increased with high-fat meal
Dronedarone distribution ✔✔✔answer✔✔✔more than 98% protein bound
Dronedarone metabolism ✔✔✔answer✔✔✔liver
Dronedarone excretion ✔✔✔answer✔✔✔feces and urine
Amiodarone blocks ✔✔✔answer✔✔✔sodium channels, calcium channels, and beta
receptors, in addition to blocking potassium channels. Amiodarone has been found to slow atrioventricular (AV) conduction and prolong AV refractoriness. It also reduces automaticity in the sinoatrial (SA) node along with the ventricles and His-Purkinje system. The actual mechanism that causes the antidysrhythmic effect is unknown.
Effects on the heart amiodarone ✔✔✔answer✔✔✔Amiodarone delays repolarization,
which prolongs the effective refractory period. This causes prolongation of the QT interval, which puts the patient at risk for torsades de pointes. Amiodarone also promotes dilation of coronary and peripheral blood vessels. Amiodarone is a highly effective drug, but with that comes potential for serious side and adverse
drug effects that can ✔✔✔answer✔✔✔limit their approved use. Amiodarone should only
be used in patients for which fewer toxic drugs have failed. It is currently indicated for ventricular tachycardia and ventricular fibrillation. It is also used with atrial dysrhythmias that are resistant to safer drugs.
Pharmacodynamic Profile of amiodarone ✔✔✔answer✔✔✔Onset: 2 to 21 days
Peak: 2 to 10 hours Duration: 50 days Half-Life: 15 to 100 days
Dronedarone blocks ✔✔✔answer✔✔✔potassium channels, which delays repolarization.
The exact mechanism of action remains unknown. Similar to amiodarone, dronedarone can also block sodium channels, calcium channels, and beta-adrenergic receptors.
Dronedarone effects on the heart ✔✔✔answer✔✔✔Dronedarone causes prolonged PR
(the length of time from the onset of atrial depolarization to the onset of ventricular depolarization) and prolonged QT, along with a widened QRS.
Dronedarone therapeutic uses ✔✔✔answer✔✔✔It reduces hospitalization for atrial
fibrillation in patients currently in sinus rhythm with a history of paroxysmal or persistent atrial fibrillation.
who have a known hypersensitivity to the drug and iodine. Another contraindication is for patients with known severe sinus bradycardia or second- or third-degree heart block
- What is the primary mechanism of action of Class III antidysrhythmic drugs? A. Block calcium channels to slow AV node conduction B. Increase vagal tone to reduce heart rate C. Prolong repolarization by blocking potassium channels D. Inhibit sodium influx in Purkinje fibers
✔✔✔answer✔✔✔C
Rationale: Class III drugs block potassium channels, prolonging repolarization and the action potential duration.
- A patient is started on amiodarone. Which of the following baseline assessments is most important before therapy begins? A. Visual acuity B. Serum sodium C. Pulmonary function tests D. Urinalysis
✔✔✔answer✔✔✔C
Rationale: Amiodarone can cause pulmonary fibrosis; pulmonary function testing is essential before and during therapy.
- Which ECG change is expected with therapeutic use of a Class III antidysrhythmic drug? A. Shortened QT interval B. Prolonged QT interval C. Inverted T waves D. ST elevation
✔✔✔answer✔✔✔B
Rationale: Class III drugs prolong the QT interval due to delayed repolarization.
- A nurse is caring for a patient on long-term amiodarone therapy. Which finding is most concerning? A. Slightly elevated liver enzymes B. Persistent dry cough and dyspnea C. Occasional nausea D. Mild photophobia
✔✔✔answer✔✔✔B
Rationale: Pulmonary toxicity is a serious adverse effect of amiodarone and may present as a dry cough and dyspnea.
- The nurse reviews a patient's lab results and notes a potassium level of 3.1 mEq/L. The patient is scheduled to receive sotalol. What should the nurse do? A. Administer the dose and encourage potassium-rich foods B. Hold the sotalol and notify the healthcare provider C. Double the next dose of sotalol D. Administer sodium bicarbonate
✔✔✔answer✔✔✔B
Rationale: Hypokalemia increases the risk of torsades de pointes with sotalol. The drug should be held until potassium is corrected.
- What adverse effect of amiodarone requires routine ophthalmologic monitoring? A. Glaucoma B. Cataracts C. Corneal microdeposits and vision changes D. Retinal detachment
✔✔✔answer✔✔✔C
Rationale: Amiodarone can cause corneal microdeposits and visual disturbances. Eye exams are part of long-term monitoring.
- Which electrolyte disturbances increase the risk of arrhythmias when using Class III drugs like dofetilide? A. Hypernatremia and hypermagnesemia B. Hypokalemia and hypomagnesemia C. Hyperkalemia and hypocalcemia D. Hyponatremia and hyperchloremia
✔✔✔answer✔✔✔B
Rationale: Low potassium and magnesium levels increase the risk of torsades de pointes when using potassium channel blockers.
- What teaching point is important for a patient prescribed oral amiodarone? A. “You can stop taking it once symptoms improve.” B. “Avoid direct sunlight and wear sunscreen.” C. “Take with grapefruit juice to improve absorption.” D. “Limit fluid intake to reduce edema.”
IV Dosage and Administration Reconstitution for amiodarone ✔✔✔answer✔✔✔Infusions
longer than 2 hours must be administered/diluted in glass or polyolefin bottles. Dilute loading dose (150 mg) in 100 mL D5W (1.5 mg/mL). Dilute maintenance dose (900 mg) in 500 mL D5W (1.8 mg/mL). Concentrations greater than 2 mg/mL cause peripheral vein phlebitis. IV Dosage and Administration rate of administration for amiodarone
✔✔✔answer✔✔✔Does not need protection from light during administration
Administer through central venous catheter (CVC) if possible, using inline filter Bolus over 10 min (15 mg/min) not to exceed 30 mg/min; then 1 mg/min over 6 hours; then 0. mg/min over 18 hours Infusions longer than 1 hour, concentration not to exceed 2 mg/mL unless CVC is used
PO Dosage and Administration for amiodarone ✔✔✔answer✔✔✔Initially, 800 to 1600
mg/day in 1 to 2 divided doses for 1 to 3 weeks. After arrhythmia is controlled or side effects occur, reduce to 600 to 800 mg/day for 4 weeks. PO Dosage and Administration for amiodarone maintenance
✔✔✔answer✔✔✔Maintenance: 400 mg/day
Because of the high risk for toxicities, amiodarone is indicated only for
✔✔✔answer✔✔✔for life-threatening dysrhythmias. Common side effects from
amiodarone include headache, peripheral neuropathy, fatigue, hypotension, bradycardia, nausea, vomiting, and constipation. Amiodarone can also cause the skin to be sensitive to sunlight, especially with higher doses. Long-term use may cause the skin to develop a blue-gray color. This is an infrequent side effect and may resolve with discontinuation of the drug. Avoidance of prolonged sun exposure can prevent this.
Amiodarone has many adverse drug effects; ✔✔✔answer✔✔✔reactions are more
common in patients with higher doses and prolonged therapy. Amiodarone has great benefits, but the potential for adverse drug effects needs to be monitored very closely because permanent injury or death can occur.
Pulmonary toxicity with amiodarone may be ✔✔✔answer✔✔✔dose related. Toxicity
manifests as hypersensitivity pneumonitis, interstitial/alveolar pneumonitis, or pulmonary fibrosis. About 10% of the cases are fatal. Baseline chest x-ray and pulmonary function tests should be obtained before the patient starts amiodarone and should be closely monitored throughout
treatment. Patients need to be monitored for symptoms (dyspnea, cough, chest pain), and the drug should be discontinued at the first sign of pulmonary dysfunction.
Cardiotoxicity ✔✔✔answer✔✔✔Amiodarone is a proarrhythmic drug that can
exacerbate current dysrhythmias and/or cause the occurrence of new dysrhythmias. It can also decrease the heart rate, leading to bradycardia and AV blocks, and it can cause hypotension and exacerbate heart failure. Patients should be closely monitored for any evidence of heart failure, such as dyspnea, edema, weight gain, and fatigue
Thyroid Toxicity ✔✔✔answer✔✔✔Long-term amiodarone therapy can cause thyroid
dysfunction. Higher doses increase the risk. Dysfunction can manifest as either hypothyroidism or hyperthyroidism. Thyroid function tests should be obtained before therapy and periodically during treatment.
Hepatotoxicity ✔✔✔answer✔✔✔Liver injury is a potential, although rarely fatal, adverse
effect of amiodarone therapy. Asymptomatic elevation of liver enzymes occurs frequently. Baseline liver function tests should be obtained and periodically during treatment. Amiodarone should be discontinued when the enzymes exceed three times the normal level.
Ophthalmic Effects ✔✔✔answer✔✔✔Rarely, amiodarone has been associated with optic
neuropathy and optic neuritis, sometimes progressing to blindness. However, a causal relationship has not been established. Patients who develop changes in visual acuity or peripheral vision should undergo ophthalmologic evaluation. If optic neuropathy or neuritis is diagnosed, discontinuation of amiodarone should be considered. Nearly all patients develop corneal micro deposits, but they do not interfere with vision.
Toxicity in Pregnancy and Breastfeeding ✔✔✔answer✔✔✔Amiodarone crosses the
placental barrier and enters breast milk and can harm the developing fetus and breastfeeding infant. Accordingly, pregnancy and breastfeeding should be avoided while using the drug and for several months after stopping it.
Dronedarone has the following contraindications: ✔✔✔answer✔✔✔Liver or lung toxicity
related to previous amiodarone use Severe hepatic impairment Pregnancy or breastfeeding Cardiac conditions
Renal impairment and/or acute kidney injury New or worsening heart failure Torsades de pointes Vasculitis Anaphylactic reactions including angioedema
Interventions for Class III Antidysrhythmic Drugs ✔✔✔answer✔✔✔Nurses must monitor
for signs and symptoms related to decompensation of the cardiac system, renal system, and/or liver dysfunction. Key items to assess for include decreased urine output (less than 1200 mL in 24 hours), edema, dyspnea, and prolonged capillary refill (greater than 3 seconds). The patient should be on a continuous cardiac monitor when antidysrhythmic drugs are administered in acute settings. It is important to note any changes in what for class III antidysrhythmic drugs
✔✔✔answer✔✔✔level of consciousness, pulse rate, cardiac rhythm, blood pressure, and
QT interval. These changes must be reported to the health care provider immediately because the regimen may need to be stopped or changed.
Class III Antidysrhythmic Drugs general teachings ✔✔✔answer✔✔✔Teach the patient to
take the prescribed drug as ordered, because drug adherence is essential. Emphasize to the patient the interaction with grapefruit juice, because it can increase blood levels of the drug, leading to toxicity. Recommend consumption of a high-fiber diet and forcing of fluids to minimize the constipation that is a common adverse effect of antidysrhythmic drugs. Teach the patient to not stop the drug abruptly.
Class III Antidysrhythmic Drugs side effects ✔✔✔answer✔✔✔Instruct the patient to
report side effects and adverse drug effects to the health care provider, including dizziness, faintness, nausea, and vomiting. Instruct the patient to report symptoms of difficulty breathing, chest pain, racing heart, weight gain, swelling, changes in baseline blood glucose levels, excess fatigue, and reduced vision. Advise the patient to avoid sunlamps and to wear sunscreen and protective clothing when out in the sun. Advise the patient to avoid alcohol, caffeine, and tobacco. Alcohol can intensify hypotensive reaction, caffeine increases catecholamine level, and tobacco promotes vasoconstriction. Teach the patient to change positions slowly because blood pressure can drop.
Patient Teaching Specific to Amiodarone ✔✔✔answer✔✔✔Advise the patient to take the
drug with food or a snack to prevent or decrease GI upset. Warn the patient that photosensitivity (sunburn and other exaggerated skin reactions to the sunlight) and photophobia (light sensitivity) can occur with use of this drug. They should use sunscreen and wear protective clothing/hat to avoid sunburn. Emphasize protection of the eyes, with wearing of sunglasses and/or tinted contact lenses. Instruct the patient to immediately report any blue-gray discoloration of the skin (often after 1 year, and especially on the face, neck, and arms), as well as any jaundice (yellow skin or eyes), unusual rash or skin reactions, nausea, vomiting, or dizziness.
Patient Teaching Specific to Dronedarone ✔✔✔answer✔✔✔Instruct the patient to take
dronedarone with food to decrease the risk of GI distress. Inform the patient that film-coated tablets should not be broken, crushed, dissolved, or divided. Instruct the patient to report common side effects, including slow heart rate, diarrhea, weakness, nausea, and skin reactions, if they persist or become severe. Advise the patient to avoid concurrent use of inhibitors of hepatic CYP3A4 (e.g., ketoconazole, clarithromycin, ritonavir), because these can make dronedarone accumulate to dangerous levels. Evaluate the therapeutic effects of Class III antidysrhythmic drugs
✔✔✔answer✔✔✔(potassium channel blockers) while minimizing adverse drug effects
such as pneumonitis, heart failure, ventricular arrhythmias, and liver failure. Ask patients about any symptoms related to decreased cardiac output caused by atrial fibrillation. With each patient encounter, reiterate the need to avoid sunlight and sunlamps and to use sunscreen and/or protective clothing. Monitoring hepatic functions is necessary because of the risk of hepatic toxicity. Amiodarone is contraindicated in a patient with which hypersensitivity?
✔✔✔answer✔✔✔Iodine allergy
Which drug can further decrease heart rate when taken with amiodarone?
✔✔✔answer✔✔✔Beta blockers
Drug-drug interactions with beta blockers can further decrease heart rate when taken with amiodarone. The use of dronedarone is contraindicated in patients with which condition?
✔✔✔answer✔✔✔Permanent atrial fibrillation
Dronedarone is contraindicated in patients who have permanent atrial fibrillation and severe, decompensated heart failure.
swelling difficulty breathing A patient is prescribed to receive an initial dose of amiodarone 800 mg and a maintenance dose of warfarin 8 mg. Which action would the nurse expect when notifying the health care provider about
the order? ✔✔✔answer✔✔✔decrease the dose of warfarin
Which statements made by the patient indicate a need for more teaching about dronedarone?
✔✔✔answer✔✔✔"I can take this without regard to food."
"If I forget to take a dose, I can double it." "It is normal to develop swelling to the feet." A patient is receiving amiodarone. During patient teaching, the nurse will explain the importance of
drug toxicity knowing amiodarone accumulates in which organs? ✔✔✔answer✔✔✔lungs
liver
