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9780521704632c14 CUFX213A/Peck 9780521618168 December 28, 2007 12:32
14 Anti-arrhythmicsBoth: supraventricular and ventricular tachyarrhythmias
Amiodarone
Amiodarone is a benzofuran derivative.Presentation
Itis presented as tablets containing 100–200 mg and as a solution containing 150 mg
per ampoule. It should be diluted in 5% dextrose before administration.Uses
Amiodarone is used in the treatment of SVT, VT and WPW syndrome. It is a complex
drug with many actions and side effects.
Aloading dose of 5 mg.kg−^1 over 1 hour followed by 15 mg.kg−^1 over 24 hours
provides a starting point for its intravenous use, which should be adjusted according
to response. When used orally treatment commences with 200 mg tds for 1 week,
followed by 200 mg bd for a further week and thereafter 200 mg od.Mechanism of action
While it has been traditionally designated a class III anti-arrhythmic, amiodarone
also demonstrates class I, II and IV activity. By blocking K+channels it slows the
rate of repolarization thereby increasing the duration of the action potential. The
refractory period is also increased.Side effects
The side effects of amiodarone will affect most patients if given for long enough
although most are reversible if treatment is stopped.
Pulmonary – patients may develop a pneumonitis, fibrosis or pleuritis. The
reported incidence is 10% at 3 years with a 10% mortality rate. However, if treatment
is stopped early enough the process may be reversed. There is some evidence to
suggest that a high FiO 2 may be a risk factor in the development of acute pulmonary
toxicity when amiodarone is used in critically ill patients.
Thyroid – both hyperthyroidism (in 0.9%) and hypothyroidism (in 6%) have been
observed and both are usually reversible. It prevents the peripheral conversion of
T4 to T3.
Hepatic – cirrhosis, hepatitis and jaundice have all been observed. Liver function
tests should be performed before and during long-term treatment.
Cardiac – when large doses are given rapidly it may cause bradycardia and
hypotension. It has a low arrhythmic potential. The QT interval may be
prolonged.
Ophthalmic – corneal microdeposits occur commonly but have little clinical signif-
icance, causing visual haloes and some mild blurring of vision. They are reversible.