Amiodarone

Amiodarone - has a broad spectrum of activity on the heart. In addition to having an anti-arrhythmic activity, it also has anti-anginal effects. This may result from its a- and b-adrenoceptor-blocking properties as well as from its calcium channel-blocking effect in the coronary vessels. It causes minimal myocardial depression. It is therefore often a first-line drug in critical care situations. It has an extremely long half-life (15–105 days). Unlike oral amiodarone, IV administration usually acts relatively rapidly (20–30 min). Oral bioavailability is 50%, therefore 600 mg PO/NG is equivalent to 300 mg IV.Overlap the initial oral and IV therapy for 16 to 24 hours. An oral loading dose regimen is necessary even when the patient has been adequately ‘loaded’ intravenously. This is because amiodarone has a large volume of distribution (4000 l) and a long half-life. The high initial plasma levels quickly dissipate as the drug binds to the peripheral lipophilic tissues. Thus a prolonged loading regimen is required.When the cause of the arrhythmia has resolved, e.g. sepsis, then amiodarone treatment can be stopped abruptly.

Uses:
Good results with both ventricular and supraventricular arrhythmias, including those associated with WPW syndrome.

Contraindications:
Iodine sensitivity (amiodarone contains iodine)
Sinus bradycardia (risk of asystole)
Heart block (unless pacemaker fitted)

Administration:
• Loading: 300 mg in 25–250 ml glucose 5% IV over 20–120 min, followed by 900 mg in 50–500 ml glucose 5% over 24 hours. If fluidrestricted, up to 900 mg can be diluted in 50 ml glucose 5% and administered centrally
• Maintenance: 600 mg IV daily for 7 days, then 400 mg IV daily for 7 days, then 200 mg IV daily Administer IV via central line. A volumetric pump should be used as
the droplet size of amiodarone may be reduced. Continuous cardiac monitoring
• Oral: 200 mg 8 hourly for 7 days, then 200 mg 12 hourly for 7 days, then 200 mg daily

How not to use amiodarone:
Incompatible with sodium chloride 0.9%
Do not use via peripheral vein (thrombophlebitis)

Adverse effects Short-term:
Skin reactions common
Vasodilation and hypotension or bradycardia after rapid infusion
Corneal microdeposits (reversible on stopping)

Long-term
Pulmonary fibrosis, alveolitis and pneumonitis (usually reversible on stopping)
Liver dysfunction (asymptomatic UP in LFT common)
Hypo- or hyperthyroidism (check TFT before starting drug)
Peripheral neuropathy,myopathy and cerebellar dysfunction (reversible on stopping)

Cautions:
Increased risk of bradycardia, AV block and myocardial depression with
b-blockers and calcium-channel antagonists
Potentiates the effect of digoxin,theophylline and warfarin – reduce dose

Organ failure:
Hepatic:worsens
Renal: accumulation of iodine may UP risk of thyroid dysfunction