Potassium channel blockers (Class 3 antiarrhythmic drugs)

Question 1

Class III antiarrhythmic drugs - 5 drugs

Answer 1

Amiodarone and dronedarone
Dofetilide
Ibutilide
Sotalol

Question 2

Class III antiarrhythmic drugs - general MOA and effects

Answer 2

Block K rectifier currents during phase 3. This causes prolongation of the ventricular action potential and refractory period.
Do not slow ventr conduction velocity or increase QRS duration significantly (except amiodarone).

Question 3

Amiodarone - Classification

Answer 3

Organic iodine compound, class III antiarrhythmic drug

Question 4

Amiodarone - onset and duration of action

Answer 4

Onset after 2 weeks (unless loading dose is given). Half-life is about 40 days (ranges between 26-107 days).

Question 5

Dronedarone - Classification

Answer 5

Nonionated analogue of amiodarone.

Question 6

Dronedarone - indications

Answer 6

Paroxysmal AF or AFL.

Question 7

Dronedarone - adverse effects

Answer 7

Liver injury and acute liver failure.

Increased mortality in pts with heart failure.

Question 8

Dronedarone - contraindications

Answer 8

Permanent A-fib. Heart failure.

Question 9

Amiodarone - MOA

Answer 9

Blocks K-channels, Ca channels, Na channels, β-adrenoceptors.

Question 10

Amiodarone - effects

Answer 10

Decrease SA node automaticity.
Decrease AV node conduction.
Prolong AV node and ventricular refractory periods.
Increase PR and QT intervals.
Slight QRS prolongation.
Powerful inhibition of ectopic pacemaker automaticity.

Question 11

Amiodarone - Adverse effects

Answer 11

Bradycardia, impaired AV conduction, QT prolongation, torsades de pointes.
Corneal microdeposits (90% of pts, usually benign).
Photosensitivity, blue-gray skin discoloration.
Hypo- and hyperthyroidism.
Tremor, ataxia, optic/peripheral neuropathy.
Hepatic dysfunction.
Pulmonary fibrosis.

Question 12

Amiodarone - interactions

Answer 12

Inhibits metabolism of e.g. digoxin, flecainide, phenytoin, procainamide, warfarin.
Increased incidence of bradycardia if given with inhalational anesthetics and CNS depressants.

Question 13

Amiodarone - indications + adm

Answer 13

Long-term: suppress supraventricular and ventricular arrhythmias - AF, AFL, SVT, VT (given orally).
Short-term: terminate VF and sustained VT, adjunct to cardioverter-defibrilators (given IV).

Question 14

Ibutilide - MOA

Answer 14

In addition to blocking the delayed rectifier K channels, it prolongs the action potential by promoting Na influx through slow inward Na channels.

Question 15

Ibutilide - indications and adm

Answer 15

AF or AFL. Adm IV infusion.

Question 16

Ibutilide and dofetilide - adverse effects

Answer 16

Torsades de pointes

Question 17

Ibutilide - contraindications

Answer 17

Prolonged QT interval, history of polymorphic VT.

Question 18

Dofetilide - indications and adm

Answer 18

AF (adm orally, for both short- and long-term treatment)

Question 19

Dofetilide - contraindications

Answer 19

Renal insufficiency (reduce doses)

Question 20

Sotalol - classifications

Answer 20

Nonselective β-blocker, Ca channel blocker. Class III antiarrhythmic drug with class II effects.

Question 21

Sotalol - indications

Answer 21

Ventr arrhythmias.
Atrial arrhythmias (AF)

Question 22

Sotalol - adverse effects

Answer 22

Dose-dependent incidence of torsades de pointes. Bronchospasm