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amiodarone

amiodarone

introduction:

  • not compatible with NSaline or heparin

actions

  • primarily a class III antiarrhythmic agent but also:
    • sodium channel blockade (class I activity)
    • mild beta blocking action (class II activity)
    • some calcium channel blockade (class IV activity)
  • directly decreases sinus node and junctional automaticity
    • dose dependent atropine resistant bradycardia
  • slows atrioventricular (AV) conduction
  • slows abnormal bypass tract conduction
  • prolongs refractory period of myocardial tissues (atria, ventricles, AV node and bypass tracts)
  • but does not significantly depress the spontaneous diastolic depolarisation of Purkinje fibres
  • prolonged QRS and QTc
  • may cause U waves and changed T waves on ECG
  • strong anti-fibrillatory action
  • increases coronary blood flow
  • reduces myocardial oxygen consumption without altering cardiac output
  • antagonistic to catecholamines and sympathomimetic agents without causing ß-adrenergic blockade

C/I

  • cardiac conduction blocks unless functioning pacemaker in situ
  • bradycardia
  • hypotension
  • lactation
  • pregnancy - class C drug
  • care with use of other cardiac drugs such as digoxin, anti-arrhythmics
  • PH thyroid disorders is a precaution for ongoing Rx

dose and usage:

IV acute dosage:

  • 5mg/kg iv up to max. 300mg in a large vein to avoid tissue necrosis from extravasation
    • administer with 100ml 5% dextrose over 20-30min if time allows, or,
    • administer with 20ml 5% dextrose over 1-2min ivi if unstable life threatening rhythm such as sustained VT or VF (after 3rd defibrillation attempt) and if unhelpful a further dose of 150 mg IV over 1 -2 minutes may be given

IV maintenance dosing:

  • maintenance infusions must be administered using glass bottles and given with 5% dextrose
  • 15-20 mg/kg bodyweight (usually 900mg) given over 24 hours
  • max. 1200mg in 24hrs

oral dosing

  • load dose 200-400mg tds for 1wk, then
  • 200-400mg bd for 1wk, then
  • 100-200mg daily

acute adverse effects include:

adverse effects of long term maintenance dosing:

  • common & increase markedly after 1st yr of use when 75% will have adverse effects!
  • symptomatic pulmonary toxicity in 10-15% > 1yr use → death in 10% of those affected
  • hepatic injury common but rarely fatal
  • aggravation of arrhythmia in 2-5% pts
  • asymptomatic corneal microdeposits in all
  • cutaneous photosensitivity 10-15%
  • blue discoloration 5%
  • symptomatic hypothyroidism 5% & hyperthyroidism 2% (inhib. periph. T4 → T3);
    • NB. each amiodarone 200 mg tablet contains organic iodine approximately 75 mg and, in the steady state, metabolism of amiodarone 300 mg yields iodine 9 mg/day, well in excess of the highest normal dietary intake
  • substantial increased LDL-cholesterol occurs frequently

some drug interactions:

  • ⇒ increased plasma concentration of:
    • digoxin, warfarin, quinidine, procainamide, phenytoin, diltiazem, encainide, flecainide;
  • ⇒ increased risk of:
  • drug interactions may persist for weeks despite cessation of amiodarone;
amiodarone.txt · Last modified: 2015/12/31 14:19 (external edit)