Friday, 26 January 2007

Amiodarone and Cardiac Dysrhythmias

Today's Blog is based on my own experiences in the treatment of cardiac dysrhythmias with Amiodarone.

My being one of the few physicians in Japan who has had experience of the use of Amiodarone (in UK patients) I hope the following will provide you with some 'hands-on' information about this drug.

When I have talked of Amiodarone in Japan I am always met with the same answer and that is Japanese patients do not want to take Amiodarone because of its side effects.

However, from my own experience, in treating many hundreds of patients with intravenous and oral preparations of Amiodarone in the UK, I have always found it to be a safe drug to use and occasionally there is the patient with amiodarone-induced side effects, but its benefits frequently outweigh its risks.

Amiodarone is usually prescribed for atrial fibrillation, but it is also used in the treatment of flutter, WPW, VT and VF.

The side effect profile includes asymptomatic corneal deposits, skin photosensitivity, slate grey discoloration of the skin (rare and with chronic use), thyroid dysfunction, liver dysfunction, pulmonary alveolitis and fibrosis, long QT/Torsade de Pointes, amongst others. However, it is a bit like reading the side effects of almost any major drug-- not all patients get all side effects and most patients get none of the serious listed side effects.

I have seen the occasional patient with thyrotoxicosis, pulmonary fibrosis and skin changes, but they are the exception rather than the rule.

I have seen many patients very effectively treated with this drug including a family relative who had Woolf Parkinson White Syndrome.

The other treatments for AF such as beta blockers, calcium channel blockers e.g. verapamil, are still effective drugs although they are not true chemical cardiovertors but rate limiting agents and both these class of drugs can reduce cardiac muscle contractility and function, which Amiodarone does not appear to do. Other drugs such as flecainide or propafenone (Class 1c) can be used in the setting of Acute AF treatment but flecainide cannot be used in patients with underlying ischaemic heart disease, unlike amiodarone, and both drugs used long term may increase mortality. Some Class 1a agents can also be used, but if toxicity occurs there can be pro-arrhythmic effects.

In the UK, in a patient with fast AF without cardiovascular compromise, unless contraindicated, in my opinion, most physicians would tend to use IV amiodarone infusion to rapidly slow the AF with an aim to chemically cardiovert the rhythm and oral therapy would then be instituted. Of course most physicians have their own personal preferences and sometimes use other drugs instead. If that fails, they would consider DC cardioversion if AF had occurred within 48 hours.

Amiodarone is usually continued in patients who do not initially cardiovert with concomittant anti-coagulation, and after 4 weeks, if there are no contraindications such as cardiac thrombosis on echocardiography, they would be electrically cardioverted. Amiodarone in conjuction with electrical cardioversion improves the cardioversion rate and patients can stay in sinus rhythm for longer.

In the UK Resuscitiation Council Guidelines over the past several years, Amiodarone has been included as the main anti-arrythmic agents to be used in VT or VF treatment rather than lignocaine/lidocaine. I have personally treated VT with Amiodarone and cardioverted patients without the need of electrical cardioversion.

The use of amiodarone can also coarsen VF from a situation of 'fine' VF making the rhythm more treatable by defibrillation.

As I am informed, at the present time, Japan has only just licensed the oral formulation of amiodarone last year but IV is still not available.

However, now that oral amiodarone is available, you now have a very effective drug at hand for the treatment of the very common cardiac problem of AF. From my own experience, and from reading the literature, this drug is regarded as safe when used correctly, and at a minimum maintenance dose of 200mg/day there should be minimal side effects.

Bear in mind that Amiodarone has a very long half life as it is very liposoluble and even on stopping such medication, the literature suggests that it may continue working for up to a year.

Always refer to your Japanese drug guides for directions when considering prescribing any new drug

There are new agents that may be available in the next few years and these include purer Class III agents such as ibutilide, dofetilide and dronedarone, the latter being a deiodinated derivative of amiodarone which has no organ toxicity and a better side effect profile.

If you would like further information about my experiences with this drug then please write including your email.

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