Amiodarone

Side effects can be severe so long term treatment is specialist initiated for life-threatening arrhythmias or where there is no alternative. Amiodarone is a very useful antiarrhythmic that possesses class III properties. It is irritant and extravasation can be serious. Patients should be fully counselled regarding the risks of long term Amiodarone therapy.

About : Always check the BNF link here

• Very useful drug but side effects are significant
• Initiation on long term therapy should be by a specialist only

Mode of action

• Potassium channel blocker primarily (Class III effect)
• Sodium and Calcium channel blocker
• Prolongs action potential duration and prolongs the effective refractory period
• Has some alpha and beta blocking activity
• Vagolytic properties, Slows conduction in the His-Purkinje system
• Slows conduction in the accessory pathway of patients with Wolff-Parkinson-White syndrome
• Also a potent vasodilator

Pharmacokinetics

• Structure similar to thyroxine - contains Iodine
• Vasodilator effects and was initially marketed as an antianginal
• Accumulates in fat and muscle
• Is liver metabolised to active form desethylAmiodarone
• Half life is long 20-100 days and more in the elderly

Indications

• Ventricular arrhythmias, Atrial fibrillation
• Emergency treatment of wide complex tachycardia

Contraindications

• Thyroid dysfunction, AV block, Sinus bradycardia

Side effects

• Bradycardia, sinus node or AV node conduction block
• Negative inotrope but less so than most other AAR
• Thyroid disease - Hypothyroidism, Hyperthyroidism
• Torsade de Pointes and long QT
• Pulmonary interstitial pneumonitis, alveolitis,
• Pulmonary fibrosis, Retroperitoneal fibrosis
• Tremor and ataxia, Cutaneous photosensitive rash
• Skin pigmentation - slate grey appearance, photosensitive
• Orchitis, Hepatitis, Reversible Corneal micro-deposits - harmless
• Peripheral neuropathy, Hypotension if given too rapidly iv

Interactions

• Amiodarone interacts with Warfarin to increase the INR
• Digoxin and Phenytoin toxicity
• Multiple others - see BNF

Dose range:You must check with BNF or drug datasheet

Dose

• Cardiac Arrest (VF / Pulseless VT): Amiodarone 300 mg IV in 20 - 30 ml of NS or D5W usually after 3rd shock. It is irritant and extravasation can be serious, so use central access where possible with 20 ml flush (G5) preferably via central line or large Venflon and flush.
• Arrhythmias: Acute use Amiodarone 300 mg IV in 250 ml 5% dextrose over 30-60 mins into a large proximal vein with a good cannulae with an additional 900 mg over 24 hours iv in 500 ml 5% Dextrose by central line or initial dose in largest cannula possible. If there is arrhythmia induced angina, hypotension or angina and compromise then administer the initial dose more rapidly. Always be ready to defibrillate.
• Long term treatment Amiodarone 200 mg PO TDS for one week, then 200 mg bd for one week and then 200 mg od
• Monitor U&E, TFTs at baseline and 6 monthly. Watch for SOB and get CXR
• Skin sensitivity can be prevented by using a sunblock

References

• Amiodarone in BNF