Antidysrhythmic drugs Flashcards
What is the mechanism of action for the Class 1 drugs?
Block voltage-sensitive Na channels and reduce depolarization rise
What is the mechanism of action for the Class 2 drugs?
Beta adrenoceptor antagonists
What is the mechanism of action for the Class 3 drugs?
Prolong the refractory period of the myocardium
What is the mechanism of action for the Class 4 drugs?
Calcium antagonists; impair impulse propagation in damaged areas of the myocardium
When do Class 1 drugs bind most strongly?
When the Na channels are open or in the refractory state
What happens to Class 1 drugs when the Na channels are closed?
It gradually dissociates, so the block resides
T/F Class 1b drugs associate and dissociate rapidly
TRUE; within the time of a normal heart beat
What is a class 1b drug/
Lidocaine
T/F Lidocaine (1B) selectively binds to refractory channels during depolarized ischemic muscle
TRUE
What is Lidocaine (1B) useful for?
Control of ventricular dysrhythmias from any reason
T/F Class 1C drugs associate/dissociate more quickly than 1B drugs
FALSE; they are slow which means they achieve a steady state block that does not vary with the stage of the cycle
What is an example of a 1C drug?
Flecainide
What is Flecanide used to treat?
Ventricular tachycardias
What are some examples of class 1A drugs?
Quinidine (Horses)
Procainamide (Dog)
What species is Quinidine used in? Whats it used for?
Horses
Reverse atrial fibrillation
Indications: supra-ventricular arrhythmias esp atrial fibrillation
Procainamide is preferred in what species to do what?
Dogs
Maintenance of ventricular arrhythmias or ventricular tachycardia
When would you NOT use Procainamide?
If the patient had a conduction block
What is the mechanism of action of the 1A drugs?
Block the Na channels, just like the 1B and 1C drugs
What effects do Beta-1 receptos have on the heart?
Increase rate and excitability
What mechanism of action do class 2 drugs have?
Beta-1 antagonists
Reduce excitability due to sympathetic overactivity and reduce AV conduction in atrial tachycardias
What are examples of Class 2 drugs?
Propranolol
Atenolol
T/F PRopranolol is the most common class 2 drug
TRUE
What special considerations come with Propranolol?
Bronchial muscle spasm is a possible SE; raise to full level over 3 days
What does Propranolol do?
HR decreased
Prevent reflex tachycardia
Lowers blood pressure and reduces ventricular hypertrophy in cardiomyopathy and hyperthyroidism
What is Atenolol used for? How is it different than Propranolol?
Used for supraventricular arrhythmias and excessive cardiac hypertrophy
May be longer acting
What is the special feature of Class 3 drugs? What do these do?
Prolongs the cardiac action potential and icnreases the refractory period
Produces pronounces ventricular and supra-ventricular anti-dysrhythmic effects
What would you use Class 3 drugs to treat?
Tachycardia
What is an example of a Class 3 drug? When would you not want to use this?
Amiodarone
Contra-indicated for used with bradycardia
What is the mechanism of action for Class 4 drugs?
Block voltage sensitive Ca channels
Shorten the plateu phase of the AP and reduce force of contraction
Inhibition of Ca suppresses ectopic beats
What are some examples of the Class 4 drugs?
Verapamil and Diltiazem
What Class 4 drug is preferred for IV administration? Long-term oral administration?
Verapamil for IV
Diltiazem: Long-term oral
What would you use Class 4 drugs to treat?
Atrial tachycardias
How do type 1A drugs differ from Class 1B and 1C drugs?
1A: can be used to treat atrial AND ventricular tachycardias
1b & 1C: Can only be used for ventricular tachycardias
All three work by blocking Na channels
What could you use to treat an atrial tachycardia?
Qunidine (1A) Horses
Propranolol and Atenolol (2)
Verapamil and Diltiazem (4)
What could you use to treat ventricular tachycardias/
Lidocaine (1B)
Flecainaide (1C; vet use probably unlikely)
Amiodarone (3)
Procainamide (1A) Dogs
