- Amiodarone acts to relax smooth muscles that line the vascular walls, decrease vascular resistance and increases cardiac index.
- IV amiodarone prolongs the QRS and QT interval.
- Decreased sinoatrial node automatically occurs with a decrease in AV node conduction velocity.
- Ectopic pacemaker automaticity is inhibited.
- Hypothyroidism may also develop post administration as amiodarone contains high levels of iodine and interferes with thyroid function.
- The lethal dose of oral amiodarone exceeds 3000mg/kg.
- Signs and symptoms of an overdose can include:
- Hypotension
- Bradycardia
- AV block
- Liver toxicity
- Mild uncommon side effects are taste disturbances, facial flushing and dizziness.
- More uncommonly, but still reportable side effects of amiodarone include lung toxicity, neurotoxicity (causing sleep disturbances and ataxia) and hyper or hypothyroidism.
- When taking oral amiodarone on a regular basis blood tests are necessary to look at levels and watch out for negative side effects.
- Can cause QT prolongation so ECGs are necessary
- When infusing Amiodarone it should be mixed with a 5% Dextrose solution as it is incompatible with a saline solution and may precipitate (insignificant when giving a bolus dose in cardiac arrest.)
- Medications such as benzodiazepines, abatacept and acalabrutinib can interfere with the metabolism of amiodarone.
- Acarbose can risk or severity of hypoglycaemia when combined with amiodarone.
- Aceclofenac with amiodarone can increase the risk or severity of hypokalaemia.
- Amiodarone is known to have a severe interaction with oral anticoagulants (such as warfarin) causing dramatic changes to the patients INR.
- Increases digoxin levels significantly and can cause a severe bradycardic episode if used with beta blockers.
Pharmacokinetics
- Amiodarone is not water soluble (it is fat/lipid soluble); the commercial preparation uses a solvent to increase its efficacy in the human body.
- Unlike the intravenous form, oral amiodarone is incompletely absorbed with approximately between 30 and 70 percent is taken up very extensively by the tissues.
- Amiodarone is largely protein bound and accumulates in adipose tissue, skin, liver, lungs, heart and smooth muscle.
- Amiodarone is metabolised to the main metabolite desethylamiodarone by enzyme cytochrome P450 found in the liver and intestines.
- Thought to have a half- life of 2.5 to 10 days
Amiodarone is primarily eliminated primarily by hepatic metabolism and biliary excretion. A small amount of the metabolite is found in the urine (practically no elimination via the renal system).
Pharmacodynamics
- Amiodarone blocks potassium currents that cause repolarisation of the heart muscle during the third phase of the cardiac action potential. This increases the duration of the action-potential thus the effective refractory period for cardiac cells, resulting in the reduction of cardiac cell excitability, suppressing cardiac ventricular and supraventricular arrhythmias
- Amiodarone does not affect membrane potential but does decrease AV conduction rates resulting in slowing of the heartrate.
- Has mild negative inotropic effects and is a peripheral and coronary vasodilatory drug.
Intravenous onset is within minutes when used as a bolus in cardiac arrest
Peak action is within 10-15 minutes but can last for up to two hours in the acute setting
- The highest potency of amiodarone in the plasma is achieved 3-7 hours after administration. The onset of action of a dose of amiodarone IV is between 1 and 30 minutes, with effects lasting from 1-3 hours.
- The half-life of amiodarone varies however research has shown it can be 58 days on average. The terminal half-life is between 14-75 days for the active metabolite. The plasma half-life after one dose ranges from 3.2-79.7 hours.
- If used for rhythm control for other than arrest situations has a slow onset of action (one to two hours).
Clinical Resources Website
St John Ambulance Western Australia Ltd (ABN 55 028 468 715) (St John WA) operates ambulance and other pre-hospital clinical services. St John WA’s Clinical Resources, including its Clinical Practice Guidelines (Clinical Resources), are intended for use by credentialed St John WA staff and volunteers when providing clinical care to patients for or on behalf of St John WA, within the St John WA Clinical Governance Framework, and only to the extent of the clinician’s authority to practice.
Other users – Terms of Use
The content of the St John WA Clinical Resources is provided for information purposes only and is not intended to serve as health, medical or treatment advice. Any user of this website agrees to be bound by these Terms of Use in their use of the Clinical Resources.
St John WA does not represent or warrant (whether express, implied, statutory, or otherwise) that the content of the Clinical Resources is accurate, reliable, up-to-date, complete or that the information contained is suitable for your needs or for any particular purpose. You are responsible for assessing whether the information is accurate, reliable, up-to-date, authentic, relevant, or complete and where appropriate, seek independent professional advice.
St John WA expressly prohibits use of these Clinical Resources to guide clinical care of patients by organisations external to St John WA, except where these organisations have been directly engaged by St John WA to provide services. Any use of the Clinical Resources, with St John WA approval, must attribute St John WA as the creator of the Clinical Resources and include the copyright notice and (where reasonably practicable) provide a URL/hyperlink to the St John WA Clinical Resources website.
No permission or licence is granted to reproduce, make commercial use of, adapt, modify or create derivative works from these Clinical Resources. For permissions beyond the scope of these Terms of Use, including a commercial licence, please contact medservices@stjohnambulance.com.au
Where links are provided to resources on external websites, St John WA:
- Gives no assurances about the quality, accuracy or relevance of material on any linked site;
- Accepts no legal responsibility regarding the accuracy and reliability of external material; and
- Does not endorse any material, associated organisation, product or service on other sites.
Your use of any external website is governed by the terms of that website, including any authorisation, requirement or licence for use of the material on that website.
To the maximum extent permitted by law, St John WA excludes liability (including liability in negligence) for any direct, special, indirect, incidental, consequential, punitive, exemplary or other loss, cost, damage or expense arising out of, or in connection with, use or reliance on the Clinical Resources (including without limitation any interference with or damage to a user’s computer, device, software or data occurring in connection with such use).
Cookies
Please read this cookie policy carefully before using Clinical Resources from St John WA.
The cookies used on this site are small and completely anonymous pieces of information and are stored on your computer or mobile device. The data that the cookies contain identify your user preferences (such as your preferred text size, scope / skill level preference and Colour Assist mode, among other user settings) so that they can be recalled the next time that you visit a page within Clinical Resources. These cookies are necessary to offer you the best and most efficient possible experience when accessing and navigating through our website and using its features. These cookies do not collect or send analytical information back to St John WA.
Clinical Resources does integrate with Google Analytics and any cookies associated with this service enable us (and third-party services) to collect aggregated data for statistical purposes on how our visitors use this website. These cookies do not contain personal information such as names and email addresses and are used to help us improve your user experience of the website.
If you want to restrict or block the cookies that are set by our website, you can do so through your browser setting. Alternatively, you can visit www.internetcookies.com, which contains comprehensive information on how to do this on a wide variety of browsers and devices. You will find general information about cookies and details on how to delete cookies from your device. If you have any questions about this policy or our use of cookies, please contact us.