- Atrial tachycardia
- Atrial fibrillation
Pharmacology of Quinidine
All antiarrhythmics decrease automaticity and increase refractory period but also have other pharmacological effects that may not be therapeutic.
- Decrease automaticity
- Increase refractory period.
- Quinidine increases AV node conduction meaning it will allow the “gate” to stay open longer.
- Never administer intravenously: It will dilate the vessels and the person will go into hypotensive shock. So this is never to be administered intravenously. However, an injectable vial of this is found in your crash carts. Normally when you see a vial, don’t always think it’s for intravenous use. This is intended for intramuscular use only. Don’t automatically assume that something in a vial that it’s for IV use. Some drugs are dangerous and lethal if given by IV but not IM.
If a person is having atrial fibrillation there are a lot of ectopic foci present. If these abnormal points on the heart are firing, the atrium is contracting too quickly and fibrillating. The AV node is protecting this random abnormal firing (fibrillation) from passing onto the ventricles. If AV node conduction is increased due to the Quinidine, the “gate” will stay open longer, and atrial arrhythmia may become ventricular! This is not good! So we add another drug!
Remember how we said that cardiac glycosides are used for CHF and only as adjunct therapy for atrial fibrillation? This is where that adjunct therapy scenario comes into play. We add a cardiac glycoside because it increases the inotropic effect (contractility) and decreases chronotropic effect (AV node conduction). So we start the patient on the cardiac glycoside. And it’s going to be a slightly higher dose because the higher dose works on the AV node (the low dose works on contractility).
Hopefully this will help stabilize the ectopic foci (the random abnormal cells firing) and that would mean we don’t have atrial fibrillation. If we stop the drug, the fibrillation would usually come right back but sometimes the area may stabilize. If we reassess the patient weeks later and they’re in good shape, do we need a cardiac glycoside anymore? (Do we need to keep closing that AV node?) No, so cardiac glycosides may only need to be there for several weeks if the ectopic foci are stabilized.
Adverse Reactions of Quinidine
Arrhythmogenic: Each one of these cardiac antiarrhythmic drugs are used to treat an arrhythmia and they can cause other cardiac arrhythmias. There have been many of these drugs pulled from the market because they potentially caused fatal arrhythmia.
Toxicity of Quinidine
Cinchonism: Quinidine comes from a bark of a tree of the class Cinchona so that’s how it got the name. When someone gets toxic on this and experiences cinchonism, they will experience:
Quinine and quinidine are pharmacologically related and you could get cinchonism from quinine as well. Quinine has been around for malaria and by the elderly for leg cramps to make it easier for them to sleep. The FDA didn’t like the elderly people taking this drug because it had the potential to create arrhythmias. Quinine was a grandfathered drug and this one drug company submitted a study that showed it was effective against malaria and they got the patent and the generics were all pulled. Now quinine costs $300/mo instead of $5/mo.
Quinidine comes in two different salts
Quinidine Sulfate is 83% quinidine.
Quinidine Gluconate is 62% quinidine (less GI issues, maybe)
They both come in 200mg, can you substitute either one? No! Because the sulfate version has more quinidine in it!