Chapter 2 - Anti-arrythmic Drugs Flashcards
Anti-arrhythmics can be classified into 4 classes (the Vaughan Williams Classification) based on their effects on the electrical behaviour of myocardial cells. What are these four classes?
Class I- membrane stabilising drugs
1A - dysopyramide
1B - lidocaine HCL
1C - flecainide acetate; propafenone HCL
Class II - Beta blockers
Class III - amiodarone; dronedarone; sotalol (also class II)
Class IV - CCBs (includes verapamil NOT dihydropyridines
*Adenosine + Digoxin - other anti-arrhythmics but do not fall under the above category
What is the mechanism of action of amiodarone?
Amiodarone is a class III membrane stabilising drug.
MOA: effects are anti-adrenergic (partial α- and β-blockers). It has haemodynamic effects (increased blood flow and systemic/coronary vasodilation). Amiodarone inhibits the metabolic and biochemical effects of catecholamines on the heart and inhibits Na+ and K+ activated ATP-ase.
What is the dosing regimen for amiodarone for a person newly initiated on it?
Typically:
200mg TDS for one week
200mg BD for one week
200mg OD thereafter
When would you consider starting someone on amiodarone for the control of AF?
‘Rhythm control’ when a drug treatment is required to maintain sinus rhythm post cardioversiom and when a standard B-blocker is not appropriate/ ineffective.
In a patient with left ventricular impairment or heart failure, which anti-arrhythmic drug should be considered for the treatment of their AF to maintain sinus rhythm?
Amiodarone HCl
BLUE BOX: MHRA/CHM safety info
Concomitant use of amiodarone with the following meds should be avoided: sofosbuvir with daclatasvir Sofosbuvir Ledipasvir Simeorevir with sofosbuvir
Why?
Risk of severe bradycardia and heart block. Avoid giving together unless other antiarrythmics can not be given.
Why should amiodarone be given as an infusion instead of an plus injection?
With intravenous use common side effect is injection-site reactions
Why is there a potential for drug interactions to occur several weeks or even months after stopping treatment with amiodarone?
Amiodarone has a long half life (anything between 20-100 days) therefore has the potential to still interact with drugs and inhibit their activity.
What are the common and specific side effects which can occur with amiodarone use?
Common side effects:
Phototoxicity, persistent slate grey skin discolouration*, taste disturbances, nausea + vomiting, sleep disorders
*due to possibility of phototoxic reactions, patients should be advised to shield skin during and for several months after treatment with amiodarone. Sunscreen should also be worn.
Specific side effects:
1) corneal microdeposits - common and reversible on withdrawal. Rarely affects vision but drivers may be dazzled by headlights at night.
2) thyroid dysfunction - hypo or hyperthyroidism or more rarely thyrotoxicosis. Amiodarone contains iodine in its chemical structure which may interfere with thyroid hormone synthesis.
3) hepatotoxicity - Pathology is very similar to alcoholic liver disease. If serum AST and ALT is persistently more than double and amiodarone is thought to be the culprit, should be discontinued. Other symptoms: jaundice
4) pulmonary toxicity - if new or progressive SOB develops, discontinue amiodarone
5) cardio toxicity - bradycardia; ventricular arrhythmia
What are the monitoring requirements needed with amiodarone?
Before treatment:
TFTs
LFTs
U&Es - specifically K+ concentration
Chest X-ray
During treatment:
TFTs, LFTs and U&Es every 6 months
Is amiodarone an enzyme inhibitor or enzyme inducer?
Enzyme inhibitor
As of 2014 NICE guidelines advise starting amiodarone before electrical cardioversion and continuing for how long after?
A) 4 weeks before procedure and continue for 4 weeks after
B) 4 weeks before procedure and continue for 3 months after
C) 4 weeks before procedure and continue for 12months after
C) 4 weeks before procedure and continue for up to 12months after to maintain sinus rhythm
