Class III

Question 1

describe class III agents

Answer 1

AMIODARONE

• Multiple effects at K+, Ca2+, Na+ channels and Beta-receptors

–> Main effect: prolong phase 3 repolarization (INcrease QT

• useful for ventricular reentry/fibrillatory arrhythmia
• EFFECTIVE IN MANY TYPES OF ARRHYTHMIAS

Question 2

describe MoA of AMIODARONE

Answer 2

• Blocks K+ channels = prolongs refractoriness and APD
• Blocks Na+ channels that are in the inactivated state
• block Ca+ channels –> slows SA node phase 4
• Slows conduction through the AV node
• Noncompetitive blockade of alpha, beta and M receptors

**EXPLAINS DIVERSE ANTIARRHYTHMIC ACTIONS

Question 3

describe main clinical apps of amiodarone

Answer 3

- EFFECTIVE IN WIDE RANGE OF ARRHYTHMIAS, nOW VERY WIDELY USED

• conversion and slwoing of AF, maintaining sinus rhythm in AF
• AV nodal reentrant tachycardia
• tachycardias assocaited with the WPW syndrome
• PO for recurrent life-threatening VT or VF resistant to other Rx
• IV for ACute termination of VT or VF and is replacing LIDOCAIN as first-line therapy for out-of-hospital cardiac arrest

Question 4

describe the pharmacology of amidoarone

Answer 4

• HIGHLY LIPID-SOLUBLE COMPOUND
• causes extremely variable and complex pharmacokinetics
• extensively metabolized to DEA

- DEA has antiarrhythmic potency > amiodarone

• rapidly concentrated in some tissues, including myocardium, but it accumulates mroe slowly in others –> Very large Vd

- UNTIL ALL TISSUES ARE SATURATED, RAPID REDISTIRBUTION OUT OF MYOCARDIUM MAY BE RESPONSIBLE FOR EARLY RECURRENCE OF ARRHYTHMIAS AFTER DISCONTINUATION OR RAPID DOSE REDUCTION

• after IV admin: T1/2 = 5-68 hours
• As tissues become saturated T1/2 = 13-103 days

Question 5

describe adverse rx to amiodarone

Answer 5

- IV> 5mg/kg decreases cardiac contractility and PVR –> HYPOTENSION

–> usual dosages improve myocardial contracitlity

• MOST SERIOUS: LETHAL INTERSTITIAL PNEUMONITIS, (more frequent in patients with preexisting lung disease

- Hyperthyroidism or hypothyroidism (diverse effects)

• photosensitivity
• acumulation of corneal microdeposists
• elevated serum hepatic enzyme levels