Review of Pharmacology - 9E (2015)

Review of Pharmacology
Class III Anti-arrhythmic drugs
B – Bretylium
I – Ibutilide
n
D – Dofetilide
A – Amiodarone
S – Sotalol
these are more efficacious at preventing a tachyarrhythmia than treating it. Because of this property
class III antiarrhythmic agents may paradoxically be more arrhythmogenic at low heart rates.
Drugs in this group are amiodarone, bretylium, sotalol, ibutilide and dofetilide.
• Amiodarone is longest acting (t 1/2
= 3-8 weeks) anti-arrhythmic drug. It possesses
action of all classes of antiarrhythmic drugs (Na + channel bloc kade, β blockade,
K + channel blockade and Ca 2+ channel blockade). Due to this property, it has
the widest anti-arrhythmic spectrum. It carries less chances of causing torsades
despite prolongation of QT interval. It contains iodine (approx. 37.5%) and can
result in hyperthyroidism (similar drug dronaderone do not contain iodine). It
Cardiovascular System
Amiodarone is longest acting
whereas adenosine is shotest
actinganti-arrhythmic drug.
can also cause hypothyroidism by inhibiting peripheral conversion of T 4
to T 3.
Other adverse effects include peripheral neuropathy, myocardial depression,
pulmonary fibrosis, hepatotoxicity, corneal microdeposits and photosensitivity.
Dronedarone is a similar drug but lacks iodine and thus adverse effects on
thyroid are not seen. Amiodarone is indicated for the treatment of refractory VT
or VF, particularly in the setting of acute ischemia. Amiodarone is also safe to
use in individuals with cardiomyopathy and atrial fibrillation, to maintain normal
sinus rhythm. It can be used for the prophylaxis of almost all arrhythmias except
torsades de’pointes.
• Bretylium is an adrenergic neuron blocking drug used only parenterally for
arrhythmias. Its major adverse effect is postural hypotension.
• Sotalol is a non-selective lipid insoluble beta blocker. It has actions of both class II
as well as class III antiarrhythmic agents. It is indicated for the treatment of atrial
or ventricular tachyarrhythmias, and AV re-entrant arrhythmias.
• Ibutilide is a structural analog of sotalol (but no beta blocking property) used for
the treatment of atrial fibrillation or atrial flutter by i.v. route only. Ibutilide is the
only antiarrhythmic agent currently approved by FDA for acute conversion of
atrial fibrillation to sinus rhythm (other drugs used in atrial fibrillation are for
controlling ventricular rate).
• Dronedarone is non-iodinated compound which has fewer adverse effects but
also less efficacy than amiodarone. It is indicated for atrial fibrillation and atrial
flutter. It has lesser incidence of pulmonary fibrosis, peripheral neuropathy and
hypothyroidism than amiodarone.
• Vernakalant is a multi-ion channel blocker that selectively prolongs atrial
refractory period without affecting ventricles. It is indicated for converting atrial
fibrillation of short duration (< 7 days) to sinus rhythm. It has little or no proarrythmic
action.
Class IV Agents
Class IV agents are the the blockers of L-type voltage gated calcium channels. They decrease the
rate of phase 4 depolarization in SA and AV nodes. This results in decreased automaticity of
SA node and decreased conduction through the AV node. Verapamil and diltiazem are mainly
indicated for PSVT and for control of ventricular rate in atrial fibrillation and flutter. Verapamil
is drug of choice for the treatment of supraventricular tachycardia (SVT) and for the
prophylaxis of PSVT.
Class V Agents
Class V agents include digoxin, adenosine, magnesium, atropine and potassium.
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