Class 1A (Anti-Arrythmics)

Question 1

What seems to be the paradox of using the drug “quinidine?”

Answer 1

It blocks the open form of the fast Na channels, as it is a class 1A drug. This prolongs the AP of cardiac myocytes and therefore increases ERP. However it is both a muscurinic blocker (would increase HR) and alpha blocker (lower BP and have reflexive tachycardia). This would do the opposite of treating arrythmias where we want slow HR.

Question 2

For what primarily do we use “quinidine?”

Answer 2

We use it for Atrial Fibrillations, in conjunction with Digoxin to slow down AV conduction to prevent the arrythmia to progress down to ventricles.

Question 3

What are the 2 main fears of A-fib?

Answer 3

Blood stasis leading to a thrombi and an embolus, and the propagation of the arrythmia through the AV node to the ventricles.

Question 4

What is the main adverse effect of Quinidine?

Answer 4

Cinchonism, which is a shared side effect of anything derived from quinine. This means CNS effects (tinnitus, occular dysfunction, CNS excitation), GI effects (diarrhea/constipation), hypotension, QRS complex prolongation, QT interval prolongation (torsades).

Question 5

What is “torsades?”

Answer 5

“Twists” all you see in an EKG are the QRS complex and this will lead to ventricular fib and death. Classic of anti-muscurinic drugs.

Question 6

Drug interactions of Quinidine?

Answer 6

Anything that causes hyper K, because it would depolarize the heart cells further making ventricle arrythmia more likely. Also Quinidine displaces digoxin from tissue binding sites.

Question 7

What DDI’s should we think of between Quinidine, Verapamil and Digoxin?

Answer 7

Verapamil and Quinidine displaces digoxin from tissue binding sites.

Question 8

What is important in Procainamide, another Class 1A drug?

Answer 8

It is similarly anti-muscurinic as Quinidine, however it is metabolized via N-acetyltransferase. However, there exists slow/fast acetylators genetically. It can cause HS rxns, SLE like symptoms and hemotoxicity. Also causes torsades like other anti-muscurinics. SLE like symptoms is the key for procainamide.

Question 9

What is very specific for drug induced SLE like symptoms in terms of lab tests?

Answer 9

+ Antihistone lab test.