EMmedonline

• Amiodarone is a class III antiarrythmi agent but exhibits properties of class I, II & IV antiarrythmic properties.

Action

• Amiodarone slows heart rate by impairing SA node function, depressing AV nodal conduction, modifying automaticity of spontaneously firing fibres in the purkinje system.

• Prolongs refractory period in the an accessory pathway.

• Amiodarone prolongs atrial and ventricular repolarisation via inhibition of potassium channels.

• Amiodarone has a weak sodium channel blocker effect . It slows upstroke velocity of phase 0 which reduces the rate of membrane depolarisation and impulse conduction.

• Amiodarone non competitively inhibits alpha and adrenergic receptor and posses both vagolytic and calcium channel blocking properties.

• The relaxses both smooth and cardiac muscle causing decrease in coronary and peripheral vascular resistance , left ventricular end diastolic pressure and systolic pressure.

Pharmacokinetics

• Amiodarone is 96 % protein bound.

• It is metabolised in liver and eliminated by biliary excretion.

• Terminal half life is 25 days after IV therapy. Chronic oral therapy half life increases upto 40 – 55 days

Indication

• VF/ Pulse less VT

• VT

• Wide complex tachyarrythmia

• Cardioversion of AF

Dose

• ACLS dose for VF/pulse less VT : 300 mg IV bolus ; 2^nd after 3 – 5 min 150 mg IV

• VT : Amiodarone : 150mg IV over 10min, 1mg/min for 6hrs then 0.5mg/min ; Max dose over 24hrs: 2.2gm

• Alternatively oral loading dose of 800 -1600mg/day for 1-3 weeks until a therapeutic response occurs and then oral maintenance dose of 200 – 600 mg/day

• Maintence of sinus rhythm in AF :

  • Oral : 400 – 600 mg daily in divided doses for 2 – 4 weeks; maintence typically 100 – 200mg OD

  • IV : 150 mg over 10 min; then 1 mg/min for 6hrs; then 0.5 mg/min for 18 hr or change to oral dosing; after 24h consider decreasing dose to 0.25 mg/min.

Availability

• Inj Cordarone 150 mg

• T. cordarone 100mg, 200 mg

Adverse Effect

• CVS : Hypotension, cardiac arrest, asystole, CCF

• Pulmonary : Pulmonary fibrosis, interstial pneumonitis or alvelolitis ,

• CNS : Peripheral neuropathy, tremors, involuntary movement

• GI: Hepatitis, elevated liver enzymes

• Ocular: corneal microdeposits, optic neuropathy and or neuritis, blurring of vision, blindness

• Metabolic: Hypothyroidism, hyperthyroidism

• Dermatologic: Photosensitivity

Warnings

• Contraindicated in patients with shelfish allergy or with an iodine.

• Amiodarone can decrease warfarin metabolism by 50% and a subsequent risk of bleeding.

• Amiodarone increase serum concentration of digoxin, procainamide, quinidine, theophylline.

• Concurrent use of amiodarone with calcium channel blocker or beta blocker may potemtiate sinus bradycardia, sinus arrest and AV block.

• CO administration of simvastatin is associated with an increased risk of rhabdomyolysis.

Note :

Inj amiodarone is compatible only in 5% dextrose.

Typically for an infusion 900mg (6amp) is added to 450 ml of 5% dextrose at infued at 30 ml/hr (1mg/min) for 6 hrs and then 15 ml/hr (0.5mg/min) .