Class 1 Antiarrhythmic Drugs
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Questions and Answers

What medications are included in Class 1a?

  • Flecainide
  • Lidocaine, Mexiletine, Phenytoin
  • Sotalol
  • Quinidine, Procainamide (correct)
  • Which of the following is in Class 1b?

  • Lidocaine (correct)
  • Procainamide
  • Flecainide
  • Quinidine
  • What is the mechanism of action of Class 1a antiarrhythmics?

  • Block K+ channels (correct)
  • Inhibit Ca2+ channels
  • Block Na+ channels (correct)
  • Agonize β-receptors
  • What is an example of a Class 1c antiarrhythmic drug?

    <p>Flecainide</p> Signup and view all the answers

    What are the cardiovascular actions of Quinidine?

    <p>Decreased cardiac contractility at high doses</p> Signup and view all the answers

    Which of the following is a side effect of Quinidine?

    <p>Cinchonism</p> Signup and view all the answers

    Procainamide is used for what purpose?

    <p>Acute treatment of certain arrhythmias</p> Signup and view all the answers

    Lidocaine has a significant effect on normal heart conduction.

    <p>False</p> Signup and view all the answers

    What is a contraindication for using Quinidine?

    <p>Cardiac failure</p> Signup and view all the answers

    What drug class does Liodocaine belong to?

    <p>Class Ib</p> Signup and view all the answers

    Study Notes

    Class 1 Antiarrhythmic Drugs

    • Class 1a includes Quinidine and Procainamide; they block Na+ channels and cause moderate decrease in slope of phase 0, prolonging repolarization and increasing action potential duration (APD) and effective refractory period (ERP).

    • Class 1b consists of Lidocaine, Mexiletine, and Phenytoin; these drugs block Na+ channels with minimal effect on the slope of phase 0 and shorten repolarization in normal fibers.

    • Class 1c is represented by Flecainide, which marks a significant increase in the slope of phase 0 with little impact on repolarization.

    Quinidine Mechanism of Action (MOA)

    • Quinidine primarily blocks activated Na+ channels, with less effect on inactivated channels, K+ channels, and Ca2+ channels at high doses.

    • It also interacts with α1 adrenoceptors and muscarinic acetylcholine receptors, leading to decreased conduction and increased refractoriness due to K+ channel blockade.

    Quinidine Cardiovascular Actions

    • Minimal change in heart rate due to balancing effects of direct action and antimuscarinic activity.

    • Variable impacts on atrioventricular (AV) conduction, with a reduction in intraventricular conduction and cardiac contractility at elevated doses due to Ca2+ channel blocking.

    • Causes vasodilation at high doses through α-blocking effects.

    Quinidine Indications

    • Rarely used now due to safer alternatives. Indicated as a second-line agent for ventricular ectopic beats, atrial flutter, atrial fibrillation, recurrent supraventricular tachycardias, and ventricular tachycardias.

    • Other applications include treating severe falciparum malaria and nocturnal leg muscle cramps.

    Quinidine Adverse Effects (AE)

    • Risk of various arrhythmias or asystole due to SA node depression and decreased conduction attributed to hyperkalemia.

    • Potential for Torsade de Pointes, syncope, or sudden death from asystole or ventricular tachycardia.

    • Digitalis toxicity in patients on digoxin, blurred vision, hallucinations, and gastrointestinal symptoms such as diarrhea can occur.

    • Sodium lactate is the preferred treatment for quinidine overdose, enhancing Na+ current and reducing drug receptor binding.

    Quinidine Contraindications (CI)

    • Should not be used in cardiac failure, digoxin-induced arrhythmias, myasthenia gravis, or thrombocytopenic purpura.

    Procainamide Properties

    • Oral bioavailability is about 75%, with 25% biotransformed into the active metabolite N-acetylprocainamide, which varies genetically among individuals.

    • About 75% of Procainamide is excreted unmodified by the kidneys, making renal function important in its use.

    Procainamide Mechanism of Action

    • Similar to Quinidine, blocking activated Na+ channels with less prominent antimuscarinic activity and no effects on Ca2+ channels or α-adrenoceptors.

    Procainamide Adverse Effects

    • Similar cardiac risks and gastrointestinal side effects as Quinidine, in addition to a lupus-like syndrome.

    Procainamide Indications

    • Used for acute treatment of specific arrhythmias such as those associated with Wolff-Parkinson-White syndrome, and when other arrhythmia treatments are ineffective or poorly tolerated.

    Lidocaine Properties

    • Class Ib antiarrhythmic focusing on the blockade of activated and inactivated Na+ channels.

    Lidocaine Electrophysiological Actions

    • Leads to slight decrease in conduction and reduced refractoriness in normal cells while increasing refractoriness in depolarized cells.

    • Particularly effective against arrhythmias linked to depolarization, but less effective in normally polarized tissues.

    Lidocaine Cardiovascular Effects

    • Causes mild decrease in contractility and heart rate at high doses, alongside vasodilation.

    Lidocaine Adverse Effects

    • Considered the least cardiotoxic antiarrhythmic, but can still lead to adverse cardiac outcomes and neurological symptoms.

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    Description

    Este quiz aborda las drogas antiarrítmicas de clase 1, incluyendo sus mecanismos de acción y efectos cardiovasculares. Se enfoca en las subclases 1a, 1b y 1c, así como en el funcionamiento de la Quinidina. Ideal para estudiantes de farmacología y cardiología.

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