1. A 54-year-old man with ischemic cardiomyopathy (EF 35%) is admitted to the ICU with hemodynamically stable sustained monomorphic ventricular tachycardia at 156 bpm refractory to overdrive pacing. IV amiodarone is ordered. The nurse asks where to place the IV and how to run the infusion. Which of the following correctly describes the administration protocol, the preferred access route, and the reason for the access preference?
A) Peripheral IV in the antecubital vein is preferred because central line placement introduces procedural risk that outweighs the minor irritant properties of amiodarone at standard infusion concentrations; the infusion runs at 1 mg/min throughout
B) Central line is mandatory, amiodarone cannot be administered peripherally under any circumstances because it causes immediate systemic phlebitis regardless of concentration or infusion rate
C) Peripheral IV is appropriate for the loading bolus only; a central line must be placed before the maintenance infusion begins because peripheral amiodarone causes ventricular fibrillation at sustained infusion rates above 0.5 mg/min
D) Central line access is preferred because amiodarone's high lipophilicity causes phlebitis and thrombophlebitis with prolonged peripheral IV infusion: the protocol is 150 mg over 10 minutes, then 1 mg/min for 6 hours, then 0.5 mg/min maintenance, with a maximum of 2.2 g in 24 hours
E) Central line is required only if the patient is on concurrent heparin infusion, amiodarone is compatible with all peripheral IV solutions and the infusion runs as a single 300 mg bolus followed by oral loading
ANSWER: D
Rationale:
Amiodarone IV is highly lipophilic and is formulated in a vehicle (polysorbate 80) that is irritating to peripheral vascular endothelium, causing phlebitis and thrombophlebitis with prolonged peripheral infusion. Central line access is therefore preferred whenever available. If only peripheral access is available, the most proximal large vein should be used and the site should be changed every 4 hours. The standard IV protocol is: 150 mg over 10 minutes (loading bolus), then 1 mg/min for 6 hours, then 0.5 mg/min as maintenance infusion, with a maximum cumulative dose of 2.2 g in 24 hours.
Option A: Option A incorrectly states that peripheral IV is preferred and that the infusion runs at a single rate of 1 mg/min throughout: the protocol uses a step-down rate and central access is preferred, not peripheral.
Option B: Option B overstates the restriction: amiodarone can be administered peripherally when central access is unavailable, but central line is preferred to minimize phlebitis risk; peripheral use is not absolutely prohibited.
Option C: Option C incorrectly states that peripheral amiodarone causes ventricular fibrillation at sustained infusion rates, phlebitis is the concern, not proarrhythmia from the peripheral route, and central line placement is not prohibited before the loading bolus.
Option E: Option E incorrectly conditions the central line requirement on concurrent heparin use and describes an incorrect dosing protocol: a single 300 mg bolus followed by oral loading is not the standard IV amiodarone regimen for VT.
2. A 68-year-old man on dofetilide 500 mcg twice daily for atrial fibrillation rhythm control is admitted for a gastrointestinal bleed. The gastroenterology team recommends cimetidine for stress ulcer prophylaxis. The cardiology fellow is asked to review. Which of the following correctly identifies the concern and proposes an appropriate alternative?
A) Cimetidine is acceptable with dofetilide because H2 receptor antagonists do not affect cardiac ion channels and the interaction risk is limited to drugs that directly block IKr: a proton pump inhibitor should not be substituted as PPIs are more potent IKr blockers than H2 antagonists
B) Cimetidine is contraindicated with dofetilide because it inhibits renal organic cation transporter 2 (OCT2), reducing dofetilide renal tubular secretion and substantially raising plasma dofetilide levels: an appropriate alternative for stress ulcer prophylaxis is a proton pump inhibitor such as pantoprazole, which does not interact with OCT2
C) Cimetidine reduces dofetilide absorption by chelating it in the gastrointestinal lumen, lowering plasma dofetilide levels and increasing the risk of atrial fibrillation recurrence, sucralfate is the preferred alternative as it does not affect dofetilide bioavailability
D) Cimetidine inhibits CYP3A4, reducing hepatic metabolism of dofetilide and raising plasma levels, famotidine is an acceptable alternative because it does not inhibit CYP3A4 and shares H2 receptor antagonism without the metabolic interaction
E) Cimetidine is safe with dofetilide at reduced doses of 200 mg twice daily, at this dose, CYP inhibition is insufficient to meaningfully affect dofetilide plasma levels and the combination can be managed with weekly outpatient QTc monitoring
ANSWER: B
Rationale:
Dofetilide is 80% renally eliminated via organic cation transporter 2 (OCT2)-mediated tubular secretion. Cimetidine is an OCT2 inhibitor: it reduces dofetilide renal clearance, causing drug accumulation, amplified QTc prolongation, and substantially elevated TdP risk. Cimetidine is explicitly listed as contraindicated in dofetilide prescribing guidelines, along with verapamil, trimethoprim, ketoconazole, and megestrol. For stress ulcer prophylaxis in this patient, a proton pump inhibitor (such as pantoprazole or esomeprazole) is an appropriate alternative, PPIs do not inhibit OCT2 and do not interact with dofetilide.
Option A: Option A incorrectly states that cimetidine is acceptable and that PPIs are more potent IKr blockers than H2 antagonists, PPIs do not meaningfully block IKr at therapeutic concentrations and do not carry the dofetilide interaction risk that cimetidine does.
Option C: Option C incorrectly describes the mechanism as gastrointestinal chelation reducing dofetilide absorption, cimetidine's interaction with dofetilide is a pharmacokinetic interaction at the renal tubule via OCT2, not a GI absorption interaction.
Option D: Option D incorrectly attributes the mechanism to CYP3A4 inhibition of hepatic dofetilide metabolism, dofetilide is primarily renally eliminated via OCT2, not hepatically metabolized by CYP3A4; famotidine does not inhibit OCT2 and is an acceptable alternative, but the mechanism stated is incorrect.
Option E: Option E incorrectly proposes dose reduction as a way to make cimetidine safe: the OCT2 interaction raises dofetilide levels regardless of the cimetidine dose used, and the prescribing contraindication is not waived by dose reduction or monitoring.
3. A 61-year-old woman is being initiated on sotalol 80 mg twice daily for paroxysmal atrial fibrillation in a monitored inpatient setting. Her baseline QTc was 438 ms. Two hours after the second dose on day 1, her QTc is 512 ms. She is asymptomatic and her serum potassium is 4.2 mEq/L. Which of the following is the correct management?
A) Continue sotalol at 80 mg twice daily and recheck the QTc in 24 hours: a QTc of 512 ms is within the expected range of QT prolongation for sotalol at this dose and does not require dose adjustment in the absence of symptoms
B) Increase the sotalol dose to 120 mg twice daily to maximize antiarrhythmic efficacy before the patient is discharged: the QTc of 512 ms indicates that adequate IKr blockade has been achieved, confirming a therapeutic response
C) Reduce sotalol to 40 mg twice daily and continue in-hospital monitoring, at the lower dose the QTc will return to an acceptable range within 48 hours and the patient can be discharged with outpatient QTc monitoring
D) Discontinue sotalol, reassess the risk-benefit ratio, and consider an alternative antiarrhythmic agent: a QTc exceeding 500 ms during sotalol initiation is a threshold that mandates drug discontinuation per guideline criteria
E) Discontinue sotalol immediately: a QTc exceeding 500 ms at any point during sotalol initiation is a mandatory stopping criterion per prescribing guidelines; continuing at any dose would carry an unacceptable torsades de pointes risk
ANSWER: E
Rationale:
The mandatory in-hospital initiation protocol for sotalol requires QTc monitoring 2 to 3 hours after each dose throughout the initiation period. If QTc exceeds 500 ms at any measurement, the drug must be discontinued. A QTc of 512 ms after only the second dose represents a significant prolongation beyond the 500 ms stopping threshold, and continuing sotalol at any dose would carry an unacceptable TdP risk. After discontinuation, the patient's clinical situation should be reassessed and an alternative antiarrhythmic strategy considered, alternatives in a patient without structural heart disease might include flecainide or propafenone with a concurrent AV nodal blocking agent. Option D correctly identifies that sotalol should be discontinued and an alternative considered, but incompletely characterizes the criterion: it describes discontinuation as appropriate for "a QTc exceeding 500 ms" generally, while Option E correctly specifies that this is a mandatory stopping criterion at any point during initiation, not merely a consideration for reassessment.
Option A: Option A is incorrect: a QTc of 512 ms exceeds the 500 ms stopping criterion and requires action, not observation, continuing at the same dose is contraindicated.
Option B: Option B is incorrect: increasing the dose when QTc already exceeds 500 ms would further amplify QT prolongation and TdP risk: this represents a dangerous misapplication of the monitoring data.
Option C: Option C is incorrect: the prescribing guideline criterion for sotalol discontinuation is QTc exceeding 500 ms, and dose reduction does not satisfy this stopping criterion, once the threshold is crossed, the drug must be stopped, not continued at a lower dose.
4. The ANDROMEDA trial demonstrated excess mortality with dronedarone in patients with severe heart failure with reduced ejection fraction. Which of the following best explains the proposed mechanistic basis for this mortality signal and distinguishes it from the mechanism responsible for the PALLAS mortality signal?
A) In ANDROMEDA, dronedarone's negative inotropic effect combined with sodium-calcium exchanger (NCX) inhibition impaired the compensatory mechanisms sustaining cardiac output in severely failing hearts, in PALLAS, the mechanism was different: dronedarone increased thromboembolic risk in permanent AF by impairing AV nodal rate control, allowing faster ventricular rates that promoted atrial stasis
B) In ANDROMEDA, dronedarone caused excess mortality through thyroid toxicity identical to amiodarone: the non-iodinated structure of dronedarone was found to be insufficient to prevent iodine-mediated thyroid dysfunction in the HFrEF population; in PALLAS, the mechanism was arrhythmia from QT prolongation
C) Both ANDROMEDA and PALLAS demonstrated mortality through the same mechanism, dronedarone's IKr blockade produced excess TdP in both populations, with the higher rate in ANDROMEDA explained by the lower ejection fractions in that trial
D) In ANDROMEDA, dronedarone caused excess mortality through direct hepatotoxicity from its benzofuran metabolite, in PALLAS, excess mortality was due to CYP3A4-mediated drug interactions raising levels of concurrent antiarrhythmic agents to toxic concentrations
E) Both ANDROMEDA and PALLAS mortality signals remain mechanistically unexplained: the trials were stopped early before adequate mechanistic data could be collected, and the contraindications are purely empirical safety signals without a proposed pharmacological basis
ANSWER: A
Rationale:
Dronedarone shares amiodarone's multi-channel profile including Class I to IV actions. In the ANDROMEDA population (severe HFrEF or recently decompensated HF), dronedarone's negative inotropic effect from calcium channel blockade and its inhibition of the sodium-calcium exchanger (NCX) are proposed to impair the compensatory mechanisms that sustaining cardiac output in severely failing hearts, where the NCX plays an important role in calcium homeostasis and where any reduction in contractility is poorly tolerated. In the PALLAS population (permanent AF at cardiovascular risk), the excess stroke, cardiovascular death, and arrhythmia are proposed to reflect different mechanisms including possible increased thromboembolic risk and proarrhythmic effects in the context of permanently remodeled atria, not the same hemodynamic mechanism as ANDROMEDA. The two trials represent two distinct contraindications: cardiac substrate matters.
Option B: Option B incorrectly attributes the ANDROMEDA mortality to thyroid toxicity, dronedarone is explicitly non-iodinated to avoid thyroid toxicity, and this was not the mechanism identified in ANDROMEDA.
Option C: Option C incorrectly states that both trials demonstrated mortality through IKr-mediated TdP, dronedarone's TdP risk is described as low to moderate, and TdP was not the primary mechanism identified in either trial.
Option D: Option D incorrectly attributes ANDROMEDA mortality to direct hepatotoxicity, hepatotoxicity has been reported as a post-marketing concern for dronedarone but was not the mechanism of excess mortality in ANDROMEDA.
Option E: Option E incorrectly states that both mortality signals are mechanistically unexplained, while mechanistic certainty is limited, proposed mechanisms based on dronedarone's pharmacology are well-described in the literature and in product labeling.
5. A 67-year-old woman has been on amiodarone 200 mg daily for 5 years for recurrent ventricular tachycardia. She is asymptomatic at her routine cardiology follow-up. Which of the following correctly describes the complete organ toxicity monitoring schedule that should be in place for this patient, and explains why monitoring must continue even if amiodarone is eventually discontinued?
A) Annual liver biopsy and pulmonary function tests only, corneal deposits and thyroid abnormalities are sufficiently common that they will be detected by symptom-driven assessment without scheduled monitoring, and monitoring is unnecessary once amiodarone is discontinued as effects resolve within 4 weeks
B) Thyroid function tests, liver function tests, and chest X-ray annually only, pulmonary function tests and ophthalmology review are reserved for patients with symptoms and are not required as routine surveillance in asymptomatic patients on standard maintenance doses
C) Thyroid function tests every 6 months, liver function tests every 6 months, annual chest X-ray and pulmonary function tests, and annual ophthalmology review, monitoring must continue for at least 12 months after amiodarone discontinuation because its half-life of 40 to 55 days means tissue levels remain clinically significant for months after stopping
D) Thyroid function tests annually, renal function tests every 6 months, and annual echocardiogram to monitor for amiodarone-induced cardiomyopathy: this schedule is based on the organ systems most commonly affected by long-term amiodarone use
E) No scheduled monitoring is required in asymptomatic patients on doses of 200 mg daily or below, as organ toxicity at this maintenance dose is negligible, monitoring is reserved for patients on doses above 400 mg daily or with total cumulative exposure exceeding 100 g
ANSWER: C
Rationale:
Amiodarone's multi-organ toxicity requires systematic scheduled monitoring across all affected organ systems. Thyroid function tests (TSH, free T4, free T3) every 6 months throughout therapy, and for at least 12 months after discontinuation, because the iodine load and drug persist in tissues long after the last dose. Liver function tests every 6 months to detect hepatotoxicity before clinical signs appear. Annual chest X-ray and pulmonary function tests to screen for pulmonary toxicity: the most serious organ toxicity. Annual ophthalmology review to detect the rare but serious complication of optic neuropathy (corneal microdeposits alone are nearly universal and not an indication to stop). The 12-month post-discontinuation monitoring requirement reflects amiodarone's extraordinary tissue half-life of 40 to 55 days, tissue levels remain clinically significant for 6 to 12 months after stopping, and thyroid dysfunction in particular can develop or progress after discontinuation. Option B correctly identifies the main organ systems but uses an annual rather than 6-monthly frequency for TFTs and LFTs, and incorrectly relegates PFTs to symptomatic patients only, PFTs are part of the scheduled surveillance.
Option A: Option A incorrectly limits monitoring to annual liver biopsy and PFTs, omits thyroid monitoring, and incorrectly states that monitoring is unnecessary after discontinuation, liver biopsy is not routine (LFTs are the standard screen), and thyroid monitoring must continue for at least 12 months post-discontinuation.
Option D: Option D incorrectly substitutes renal function tests and echocardiogram for the established monitoring schedule, amiodarone does not cause cardiomyopathy and is not renally toxic; these are not part of its monitoring protocol.
Option E: Option E incorrectly states that monitoring is unnecessary at 200 mg daily, organ toxicity from amiodarone is dose- and duration-dependent and occurs at maintenance doses; the 200 mg daily dose reduces but does not eliminate toxicity risk over 5 years of therapy.
6. A 55-year-old man with no structural heart disease presents to the emergency department with symptomatic atrial flutter of 4 hours duration, ventricular rate 140 bpm, hemodynamically stable. His QTc is 418 ms, potassium 4.3 mEq/L, and magnesium 2.1 mg/dL. The emergency physician selects ibutilide for pharmacologic cardioversion. Which of the following correctly describes ibutilide's mechanism, expected efficacy for this specific arrhythmia, and the post-procedure monitoring plan?
A) Ibutilide blocks IKr only, producing QT prolongation equivalent to dofetilide; cardioversion rates are 30 to 40% for both atrial flutter and atrial fibrillation; the patient may be discharged 60 minutes after infusion once QTc has returned to within 20 ms of baseline
B) Ibutilide is an oral agent loaded over 24 hours before cardioversion, achieving flutter termination in approximately 80% of cases; monitoring is limited to symptom assessment as the drug's short half-life prevents QT-related complications after the loading period
C) Ibutilide blocks IKr and also activates a slow sustained inward sodium current: this dual mechanism produces potent APD prolongation effective for acute cardioversion; atrial flutter responds in approximately 65 to 70% of cases (more than AF at 40 to 60%) due to its organized re-entrant circuit; continuous cardiac monitoring for at least 4 hours post-infusion is mandatory given the 4 to 8% TdP risk
D) Ibutilide blocks IKr and activates a slow inward sodium current, producing potent APD prolongation; atrial flutter cardioversion rates are approximately 65 to 70%, higher than atrial fibrillation (40 to 60%) due to flutter's organized re-entrant circuit; mandatory continuous monitoring for at least 4 hours is required given its 4 to 8% TdP risk: the highest among Class III agents
E) Ibutilide activates L-type calcium channels in addition to blocking IKr, producing calcium-mediated triggered activity termination; it is equally effective for atrial flutter and atrial fibrillation (65% for both); 2-hour post-infusion monitoring is standard once QTc has normalized
ANSWER: D
Rationale:
Ibutilide has a dual mechanism: IKr blockade combined with activation of a slow, sustained inward sodium current. This produces rapid, potent APD prolongation effective for acute pharmacologic cardioversion. Atrial flutter cardioversion rates are approximately 65 to 70%, which is higher than for atrial fibrillation (40 to 60%) because flutter's organized macro-re-entrant circuit is more susceptible to termination by refractoriness prolongation than the multiple disorganized wavelets of AF. The TdP risk of 4 to 8% is the highest among Class III agents, making mandatory continuous cardiac monitoring for at least 4 hours post-infusion essential, with resuscitation equipment immediately available. This patient is well-prepared for ibutilide: his QTc is normal, electrolytes are adequate, he has no structural heart disease, and the arrhythmia is of short duration. Option C correctly describes ibutilide's mechanism, efficacy, and monitoring requirements and is a very close second option, but Option D is preferred as the more complete and precisely worded answer explicitly identifying the TdP risk as the highest among Class III agents, which is a key distinguishing clinical fact.
Option A: Option A incorrectly states that ibutilide blocks IKr only: its second mechanism is slow inward sodium current activation, not absent, and incorrectly states cardioversion rates of 30 to 40% for flutter; 60-minute monitoring is inadequate given the 4 to 8% TdP risk.
Option B: Option B incorrectly describes ibutilide as an oral agent loaded over 24 hours, ibutilide is IV only, administered acutely, and post-infusion monitoring is mandatory.
Option E: Option E incorrectly attributes L-type calcium channel activation to ibutilide, ibutilide activates a slow inward sodium current, not ICaL, and incorrectly states equal efficacy for flutter and AF with 2-hour monitoring.
7. A 74-year-old woman with dofetilide-treated atrial fibrillation develops recurrent torsades de pointes on telemetry. Each TdP episode is preceded by a short-long-short RR interval sequence, with a prolonged pause after each episode before sinus rhythm resumes. IV magnesium 2 g has been given twice in the past hour with only partial suppression. Dofetilide has been withheld and electrolytes are normal. Which of the following identifies the specific TdP mechanism operating here and the next correct management step?
A) This is pause-dependent TdP, in which the post-extrasystolic pause maximally prolongs APD at the slow effective rate and generates early afterdepolarizations: the next step is to eliminate the pauses by increasing heart rate with IV isoproterenol infusion or temporary transvenous overdrive pacing at 90 to 110 bpm
B) This is catecholamine-sensitive TdP driven by sympathetic surges generating delayed afterdepolarizations: the next step is IV beta-blockade with metoprolol 5 mg to suppress adrenergic triggering and reduce the DAD amplitude below the threshold for triggered activity
C) This is re-entrant TdP sustained by a fixed anatomical substrate of fibrosis: the next step is synchronized DC cardioversion at 200 J to interrupt the macro-re-entrant circuit and restore organized ventricular activation
D) This is automaticity-driven TdP originating from a focus of abnormal phase 4 depolarization in the His-Purkinje system: the next step is IV lidocaine 1 mg/kg to suppress phase 4 automaticity selectively in the His-Purkinje system without affecting ventricular myocardium
E) This is triggered TdP driven by delayed afterdepolarizations from calcium overload secondary to dofetilide's positive inotropic effect: the next step is IV verapamil 5 mg to reduce intracellular calcium loading and abolish DAD-mediated triggered activity
ANSWER: A
Rationale:
The short-long-short RR interval sequence with a prolonged pause preceding each TdP episode is the hallmark of pause-dependent (bradycardia-dependent) TdP. The pause following a premature beat creates a long RR interval that maximally prolongs APD at the slow effective rate, precisely the condition that most amplifies reverse use-dependence of IKr blockade and most favors early afterdepolarization (EAD) formation. When magnesium alone is insufficient to suppress recurrent pause-dependent TdP, the definitive management is to eliminate the pauses by increasing heart rate above the threshold at which EADs form. IV isoproterenol infusion or temporary transvenous overdrive pacing at 90 to 110 bpm achieves this, by preventing the pauses, APD shortens, EADs are suppressed, and TdP terminates.
Option B: Option B incorrectly identifies the mechanism as catecholamine-sensitive delayed afterdepolarization-driven TdP: the short-long-short pattern and pause-dependence identify EAD-driven pause-dependent TdP, not DAD-driven adrenergic TdP; beta-blockade would slow the heart rate and worsen pause-dependent TdP.
Option C: Option C incorrectly describes TdP as a fixed anatomical re-entrant circuit amenable to DC cardioversion, TdP is a triggered arrhythmia driven by EADs, not a fixed re-entrant substrate; cardioversion may terminate an individual episode but does not address the underlying EAD mechanism and the episodes will recur.
Option D: Option D incorrectly attributes TdP to phase 4 automaticity in the His-Purkinje system, TdP is EAD-mediated triggered activity, not abnormal automaticity; lidocaine may shorten APD modestly but is not the management for pause-dependent TdP.
Option E: Option E incorrectly attributes TdP to dofetilide's positive inotropic effect causing calcium overload and DADs, dofetilide is not a positive inotrope and does not cause calcium overload; verapamil is contraindicated with dofetilide through the OCT2 interaction.
8. A 69-year-old man with heart failure with reduced ejection fraction (EF 30%) and persistent atrial fibrillation has failed two electrical cardioversions. His cardiologist proposes dofetilide. His baseline QTc is 452 ms and creatinine clearance is 65 mL/min. Which of the following correctly assesses his eligibility for dofetilide initiation?
A) Dofetilide initiation is appropriate: a QTc of 452 ms is within the acceptable range for patients with HFrEF because the DIAMOND-CHF trial enrolled patients with baseline QTc values up to 480 ms, and the 440 ms threshold applies only to patients without structural heart disease
B) Dofetilide initiation is appropriate at the standard dose of 500 mcg twice daily, his CrCl of 65 mL/min places him in the standard dosing tier and his QTc, while mildly prolonged, does not contraindicate initiation in a patient with established HFrEF where the benefit-risk ratio favors treatment
C) Dofetilide initiation is not appropriate at this time: a baseline QTc of 452 ms exceeds the 440 ms threshold (or 500 ms in bundle branch block) required to initiate dofetilide; proceeding risks further QTc prolongation above 500 ms and an unacceptable torsades de pointes risk during the mandatory initiation monitoring period
D) Dofetilide initiation is appropriate provided that the QTc is rechecked after the first dose and the infusion is slowed if the QTc rises above 480 ms: the 440 ms threshold is a soft guideline recommendation rather than a mandatory criterion in patients with HFrEF
E) Dofetilide initiation is contraindicated in all patients with HFrEF and baseline QTc above 420 ms: the DIAMOND-CHF trial excluded patients with QTc above 420 ms and the trial results cannot be applied to patients with longer baseline QT intervals
ANSWER: C
Rationale:
Dofetilide prescribing guidelines specify that the baseline QTc must be below 440 ms in patients with normal intraventricular conduction (or below 500 ms in patients with bundle branch block) before initiation. This patient's baseline QTc of 452 ms exceeds the 440 ms threshold, making dofetilide initiation inappropriate at this time. The rationale is that starting dofetilide in a patient with an already prolonged QTc creates a higher risk of crossing the 500 ms stopping threshold during initiation and a greater absolute TdP risk. Correctable causes of QT prolongation should be addressed first, electrolyte abnormalities, concomitant QT-prolonging drugs, and other reversible factors. If the QTc normalizes below 440 ms after correction of contributing factors, dofetilide initiation can be reconsidered.
Option A: Option A incorrectly states that the 440 ms threshold does not apply to HFrEF patients: the QTc threshold is a universal prescribing requirement for dofetilide regardless of the underlying cardiac diagnosis.
Option B: Option B incorrectly states that the mildly prolonged QTc does not contraindicate initiation: the 440 ms threshold is a hard prescribing criterion, not a clinical judgment call adjusted by indication.
Option D: Option D incorrectly characterizes the 440 ms threshold as a soft recommendation: it is a mandatory prescribing criterion specified in dofetilide's approved labeling, not a guideline preference.
Option E: Option E incorrectly states the threshold as 420 ms and conflates trial enrollment criteria with prescribing thresholds: the approved QTc threshold for dofetilide initiation is 440 ms, not 420 ms, and this is based on prescribing guidelines rather than DIAMOND-CHF enrollment criteria.
9. A 72-year-old man with atrial fibrillation is anticoagulated with warfarin (INR 2.5, stable for 6 months) and is started on amiodarone 200 mg daily for rhythm control. His cardiologist asks the pharmacist to advise on warfarin management. Which of the following correctly describes the interaction management plan, including timing, monitoring schedule, and the implication if amiodarone is later discontinued?
A) No warfarin dose adjustment is needed at initiation, amiodarone's interaction with warfarin is a class effect seen only with IV amiodarone at loading doses above 600 mg; at the oral maintenance dose of 200 mg daily, CYP2C9 inhibition is insufficient to raise INR above the therapeutic range
B) The warfarin dose should be reduced by one-third to one-half at amiodarone initiation, with INR rechecked within 1 to 2 weeks and then monitored closely for 4 to 8 weeks as amiodarone accumulates, if amiodarone is later discontinued, INR must continue to be monitored for months because amiodarone's tissue half-life of 40 to 55 days means CYP2C9 inhibition persists long after the last dose
C) The warfarin dose should be increased by 25% to compensate for amiodarone's competitive displacement of warfarin from CYP2C9 binding sites, which transiently reduces warfarin efficacy during the first 4 weeks of amiodarone therapy before equilibrium is reached
D) The warfarin dose should be reduced once by 20% at amiodarone initiation, then left unchanged indefinitely, after the initial INR stabilizes on the combined regimen at 4 weeks, no further monitoring adjustments are required unless INR becomes supratherapeutic again
E) Amiodarone should be stopped and the patient switched to a direct oral anticoagulant before amiodarone is initiated: all oral amiodarone formulations are contraindicated with warfarin due to the risk of life-threatening bleeding from unpredictable INR elevation
ANSWER: B
Rationale:
Amiodarone inhibits CYP2C9 and displaces warfarin from albumin binding sites, raising INR by a clinically significant amount at all oral doses including 200 mg daily. The warfarin dose should be proactively reduced by one-third to one-half when amiodarone is started. INR should be rechecked within 1 to 2 weeks and monitored closely for 4 to 8 weeks, because the interaction builds gradually as amiodarone accumulates in tissues over its 40 to 55 day half-life. Critically, if amiodarone is later discontinued, the CYP2C9 inhibitory effect does not resolve immediately, amiodarone's prolonged tissue half-life means that CYP2C9 inhibition persists for weeks to months after the last dose, and INR must continue to be monitored during this washout period to detect the gradual reduction in anticoagulant effect as amiodarone clears.
Option A: Option A incorrectly states that oral amiodarone at 200 mg daily does not produce meaningful CYP2C9 inhibition: the interaction occurs at all oral maintenance doses and warfarin dose adjustment is always required.
Option C: Option C inverts the mechanism: amiodarone inhibits CYP2C9, reducing warfarin metabolism and raising INR; it does not competitively displace warfarin from CYP2C9, which would reduce anticoagulant effect.
Option D: Option D incorrectly states that a single 20% dose reduction and 4-week stabilization eliminates the need for ongoing monitoring: the interaction evolves over months as amiodarone accumulates and requires ongoing INR surveillance, not one-time dose adjustment.
Option E: Option E incorrectly states that amiodarone is contraindicated with warfarin: the combination is used clinically and managed with dose adjustment and monitoring; switching to a DOAC may be clinically appropriate but is not mandated by a prescribing contraindication.
10. A clinical pharmacist is asked to prepare a teaching summary on dronedarone contraindications for a cardiology nursing team. Which of the following correctly distinguishes the two major trial-based contraindications to dronedarone and explains why they represent separate clinical constraints that must each be evaluated independently?
A) Both contraindications derive from the same trial: ANDROMEDA enrolled patients with either permanent AF or HFrEF and demonstrated excess mortality in both subgroups; the two contraindications are therefore not independent but represent a single trial's findings applied to two patient subgroups
B) The PALLAS contraindication (permanent AF) was established first and subsumes the ANDROMEDA contraindication (HFrEF), any patient with permanent AF and HFrEF need only be assessed against the PALLAS contraindication, as the more restrictive criterion applies
C) Both contraindications are based on QT-prolongation-mediated TdP mortality: PALLAS showed TdP excess in permanent AF and ANDROMEDA showed TdP excess in HFrEF; they share the same mechanism and represent a single class effect of dronedarone's IKr blockade
D) The ANDROMEDA contraindication (HFrEF or recently decompensated HF) applies regardless of AF type, and the PALLAS contraindication (permanent AF) applies regardless of ejection fraction: a patient with permanent AF and preserved EF is contraindicated by PALLAS alone, while a patient with paroxysmal AF and HFrEF is contraindicated by ANDROMEDA alone; a patient with both conditions carries both contraindications
E) The ANDROMEDA trial demonstrated excess mortality in patients with severe HFrEF or recently decompensated HF (mechanism: negative inotropy and NCX inhibition in failing hearts), while PALLAS demonstrated excess stroke, cardiovascular death, and arrhythmia in patients with permanent AF (a distinct population and mechanism): these are two independent contraindications, each requiring evaluation regardless of the other
ANSWER: E
Rationale:
Dronedarone has two independent trial-based contraindications that must each be evaluated separately. ANDROMEDA (2008) enrolled patients with severe HFrEF or recently decompensated heart failure and was stopped early due to excess mortality: the proposed mechanism involves dronedarone's negative inotropic and NCX-inhibitory effects impairing the compensatory mechanisms that sustain cardiac output in severely failing hearts. PALLAS (2011) enrolled patients with permanent AF at cardiovascular risk and was stopped early due to excess rates of stroke, cardiovascular death, and arrhythmia: a different population with a different proposed mechanism involving thromboembolic and proarrhythmic effects in permanently remodeled atria. These are independent contraindications: a patient with preserved EF and permanent AF carries the PALLAS contraindication; a patient with paroxysmal AF and HFrEF carries the ANDROMEDA contraindication; a patient with both conditions carries both. Option D correctly identifies the independence of the two contraindications and gives accurate examples, but attributes an incorrect causal structure: it implies the contraindications are mutually exclusive ("alone" language), while Option E more clearly states they are independent and additive.
Option A: Option A incorrectly states that both contraindications derive from the same trial: ANDROMEDA and PALLAS are distinct trials with different patient populations, endpoints, and proposed mechanisms.
Option B: Option B incorrectly implies that the PALLAS contraindication subsumes ANDROMEDA: they are independent constraints that must be assessed separately.
Option C: Option C incorrectly attributes both mortality signals to QT-prolongation-mediated TdP: this is not the mechanism proposed for either trial; dronedarone's TdP risk is described as low to moderate, and TdP was not the primary cause of excess events in either ANDROMEDA or PALLAS.
11. A 65-year-old man with paroxysmal atrial fibrillation and stage 3a chronic kidney disease (creatinine clearance 52 mL/min) is a candidate for sotalol. His baseline QTc is 432 ms and he has no history of heart failure or prior myocardial infarction. Which of the following correctly applies sotalol's renal dosing requirements to this patient?
A) Sotalol can be used in this patient, but his CrCl of 52 mL/min (in the 40 to 60 mL/min range) requires extension of the dosing interval to every 36 to 48 hours rather than the standard twice-daily dosing, in-hospital initiation with 3 days of continuous telemetry and QTc monitoring remains mandatory at this dose interval
B) Sotalol can be used at standard twice-daily dosing of 80 mg because 52 mL/min is above the 40 mL/min contraindication threshold and no dose adjustment is required until CrCl falls below 40 mL/min
C) Sotalol is contraindicated in this patient because any creatinine clearance below 60 mL/min represents the renal dosing threshold, once CrCl falls below 60 mL/min, the drug accumulation risk is equivalent to patients with CrCl below 40 mL/min
D) Sotalol requires a 50% dose reduction to 40 mg twice daily rather than interval extension, reducing the dose rather than extending the interval provides equivalent plasma level control with a more favorable daily pharmacodynamic profile
E) Sotalol requires interval extension to every 36 to 48 hours in this patient, but in-hospital initiation is not required when the dose interval is extended: the 3-day monitoring requirement applies only to patients receiving standard twice-daily dosing
ANSWER: A
Rationale:
Sotalol's renal dose adjustment protocol is based on creatinine clearance tiers. For CrCl greater than 60 mL/min, standard dosing of 80 to 160 mg twice daily is used. For CrCl between 40 and 60 mL/min: this patient's range at 52 mL/min: the dosing interval is extended to every 36 to 48 hours to allow for adequate drug clearance between doses. For CrCl below 40 mL/min, sotalol is contraindicated. Critically, the mandatory 3-day in-hospital monitoring requirement applies regardless of the dose interval used: the TdP risk is present whether dosing is twice daily or at an extended interval, and telemetry monitoring is non-negotiable.
Option B: Option B incorrectly states that no dose adjustment is required above 40 mL/min: the interval extension requirement applies specifically to CrCl between 40 and 60 mL/min; using standard twice-daily dosing at 52 mL/min would cause drug accumulation and amplified QTc prolongation.
Option C: Option C incorrectly states the dosing threshold as 60 mL/min for contraindication, CrCl below 60 mL/min requires interval extension, not contraindication; the contraindication threshold is below 40 mL/min.
Option D: Option D incorrectly proposes dose reduction as an alternative to interval extension, sotalol's renal dose adjustment is by interval extension (every 36 to 48 hours), not by dose concentration reduction; the 40 mg twice daily approach is not the established adjustment method.
Option E: Option E incorrectly states that in-hospital initiation is not required with extended interval dosing: the mandatory 3-day telemetry requirement applies to all patients initiating sotalol regardless of dose interval.
12. A 68-year-old man with atrial fibrillation and hypercholesterolemia is started on amiodarone 200 mg daily. His current statin is simvastatin 40 mg nightly, which has been well tolerated for 3 years. Which of the following correctly identifies the concern with this combination and the appropriate management?
A) No adjustment is needed, amiodarone inhibits CYP2D6, which has no significant role in simvastatin metabolism; the combination is safe at all simvastatin doses and no monitoring beyond routine annual creatinine kinase measurement is required
B) Simvastatin should be increased to 80 mg nightly to compensate for amiodarone's induction of CYP3A4, which accelerates simvastatin metabolism and reduces plasma statin levels, without dose increase, cardiovascular risk reduction will be inadequate
C) Amiodarone inhibits CYP3A4, raising simvastatin plasma levels and increasing myopathy and rhabdomyolysis risk, simvastatin doses above 20 mg should be avoided with amiodarone; an appropriate switch is to pravastatin or rosuvastatin, which are not significantly metabolized by CYP3A4
D) Amiodarone inhibits CYP2C9, raising simvastatin levels by the same mechanism as its interaction with warfarin, simvastatin should be reduced to 10 mg nightly and CK levels monitored monthly
E) Simvastatin competitively inhibits amiodarone's CYP3A4 metabolism, raising amiodarone plasma levels and increasing organ toxicity risk, simvastatin should be discontinued and replaced with ezetimibe, which does not affect CYP3A4
ANSWER: C
Rationale:
Amiodarone inhibits CYP3A4, the primary enzyme responsible for simvastatin and lovastatin metabolism. This raises statin plasma levels, increasing the risk of statin-induced myopathy and rhabdomyolysis. The FDA label for simvastatin specifies that doses above 20 mg should be avoided in patients receiving amiodarone. The preferred management is to switch to a statin that is not significantly metabolized by CYP3A4, pravastatin is eliminated primarily by non-CYP mechanisms and rosuvastatin undergoes minimal CYP3A4 metabolism; both are appropriate alternatives that provide equivalent or superior LDL reduction without the interaction risk.
Option A: Option A incorrectly identifies CYP2D6 as the relevant enzyme, simvastatin is metabolized by CYP3A4, not CYP2D6, and the interaction with amiodarone operates through CYP3A4 inhibition; the combination at 40 mg simvastatin is not safe.
Option B: Option B inverts the mechanism: amiodarone inhibits CYP3A4, it does not induce it, inhibition raises statin levels; induction would lower them. Increasing simvastatin would amplify the toxicity risk.
Option D: Option D incorrectly identifies CYP2C9 as the relevant enzyme for the statin interaction: the warfarin interaction operates through CYP2C9, but the simvastatin interaction operates through CYP3A4; these are distinct metabolic pathways.
Option E: Option E incorrectly attributes CYP3A4 inhibition to simvastatin acting on amiodarone: it is amiodarone that inhibits CYP3A4, not simvastatin; simvastatin is a CYP3A4 substrate, not an inhibitor of that enzyme.
13. Three patients with symptomatic paroxysmal atrial fibrillation present for rhythm control. Patient 1: 48-year-old woman, no structural heart disease, EF 62%, QTc 408 ms, CrCl 90 mL/min. Patient 2: 61-year-old man, prior MI 2 years ago, EF 52%, QTc 438 ms, CrCl 72 mL/min. Patient 3: 69-year-old woman, ischemic cardiomyopathy, EF 28%, QTc 430 ms, CrCl 58 mL/min. Which of the following correctly matches each patient to their available antiarrhythmic options based on structural substrate constraints?
A) Patient 1: amiodarone only (safest agent across all populations); Patient 2: amiodarone or dronedarone (CAD with preserved EF); Patient 3: amiodarone, dofetilide, or sotalol (all Class III agents acceptable in HFrEF provided QTc is below 440 ms)
B) Patient 1: flecainide, propafenone, sotalol, dronedarone, or amiodarone (no structural constraint); Patient 2: sotalol, dofetilide, dronedarone (EF preserved, no recent decompensation), or amiodarone (Class Ic contraindicated by CAST); Patient 3: amiodarone or dofetilide only (HFrEF, flecainide, propafenone, sotalol, and dronedarone all contraindicated or carry mortality signals)
C) Patient 1: flecainide or propafenone only (Class Ic preferred in young patients without structural disease); Patient 2: amiodarone only (the only agent safe across all structural substrates); Patient 3: sotalol or dofetilide (Class III agents without the organ toxicity burden of amiodarone)
D) Patient 1: any antiarrhythmic agent including Class Ic, Class III, and dronedarone; Patient 2: amiodarone only (all other agents contraindicated in CAD regardless of ejection fraction); Patient 3: dofetilide only (amiodarone is contraindicated in HFrEF due to negative inotropic effects at oral maintenance doses)
E) Patient 1: sotalol or amiodarone only (Class Ic agents are avoided in all women of childbearing age regardless of cardiac substrate); Patient 2: dofetilide or amiodarone (sotalol contraindicated in all patients with prior MI); Patient 3: amiodarone only (dofetilide requires CrCl above 60 mL/min for initiation and her CrCl of 58 mL/min is below this threshold)
ANSWER: B
Rationale:
Patient 1 has no structural heart disease, making all antiarrhythmic classes pharmacologically available, Class Ic agents (flecainide, propafenone), sotalol, dronedarone, and amiodarone are all options, with the choice guided by side effect profile, QTc, and patient preference. Patient 2 has prior MI with preserved EF, Class Ic agents (flecainide, propafenone) are contraindicated by CAST in structural heart disease including post-MI regardless of current EF. Sotalol, dofetilide, dronedarone (with preserved EF and no recent decompensation), and amiodarone are all available options. Patient 3 has HFrEF (EF 28%), only amiodarone and dofetilide are appropriate. Flecainide and propafenone are contraindicated (CAST), sotalol should be avoided with EF below 40% (SWORD signal), and dronedarone is contraindicated (ANDROMEDA). Dofetilide requires dose adjustment for CrCl 40 to 60 mL/min (250 mcg twice daily), her CrCl of 58 mL/min is within the adjustable range, not below the contraindication threshold of 20 mL/min.
Option A: Option A incorrectly restricts Patient 1 to amiodarone only and incorrectly includes sotalol for Patient 3, sotalol is avoided in HFrEF.
Option C: Option C incorrectly restricts Patient 1 to Class Ic agents only and incorrectly restricts Patient 2 to amiodarone only, multiple agents are available in CAD with preserved EF.
Option D: Option D incorrectly restricts Patient 2 to amiodarone only, sotalol, dofetilide, and dronedarone (with preserved EF) are all appropriate in CAD with preserved EF, and incorrectly states amiodarone is contraindicated in HFrEF.
Option E: Option E incorrectly restricts Class Ic agents based on sex rather than cardiac substrate, incorrectly states sotalol is contraindicated in all patients with prior MI regardless of EF, and incorrectly sets the dofetilide CrCl threshold at 60 mL/min: the contraindication threshold is CrCl below 20 mL/min.
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