Amiodarone

Amiodarone is a complex drug, acting in many ways (Gonzalez et al. 1998). It works by increasing the duration of the action potential, though it also has antisympathetic and calcium channel-blocking properties (Taylor 2002). Amiodarone reduces membrane excitability and increases the refractory period, therefore making cardiac cells less susceptible to transmitting ectopic impulses.

A number of studies have shown the effectiveness of amiodarone during cardiac arrest. In the Amiodarone in Out-of-Hospital Resuscitation of Refractory Sustained Ventricular Tachycardia (ARREST) Trial (Kudenchuk et al. 1999), it proved better than placebo in terminating VF/VT. Similarly, the Amiodarone versus Lidocaine in Prehospital Ventricular Fibrillation Evaluation (ALIVE) (Dorian et al. 2002) reported improved results using amiodarone rather than lignocaine. Even if these trials did not demonstrate increased survival to discharge and beyond (Taylor 2002), there is sufficient evidence to recommend the use of amiodarone in VF/VT cardiac arrest if the initial three-shock sequence has been unsuccessful.

• Because of its unique pharmacological properties, amiodarone is effective in the management of both atrial and ventricular rhythms.

• The dosage given will depend on the situation and administration should preferably be via a central vein.

• After three unsuccessful defibrillator shocks for VF/VT cardiac arrest, 300mg diluted in 5% dextrose up to a volume of 20 ml should be administered after adrenaline/epinephrine. Pre-filled syringes are available.

• In the peri-arrest period, amiodarone is effective in both broad and narrow complex tachyarrhythmias. The dose is 150 mg delivered over ten minutes and repeated if necessary. Alternatively 300 mg can be given over one hour.

• The usual maximum daily dose of amiodarone is 1.2g (British National Formulary 2003), but this can be increased up to 2g (Resuscitation Council UK 2000).

• Intravenous infusion may be necessary and local policies should be consulted for these. It should be remembered that all antiarrhythmic drugs are also pro-arrhythmic.

• The major side-effects of amiodarone are hypotension and bradycardia.

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