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Class I Anti-Arryhthmics - #PHARMFAX

Class I Antiarryhthmics from the Vaughan Williams classification are primarily voltage gated sodium channel blockers.

 


Class I Antiarrythmics from the Vaughan Williams classification are primarily voltage gated sodium channel blockers. They are then broken down into three subsets; 1a, b, and c, They work by blocking the rapid inward sodium current, slowing the rise of action potentials and reduces the phase 0 slope.


1a Antiarrythmics are Procainamide, Quinidine, and Disopyramide. As a subgroup, they have intermediate kinetics and contain both sodium and potassium channel blockade. This results in both QRS widening and QTc prolongation.

1b consists of lidocaine and mexilitine. These agents have rapid kinetics, weak sodium channel blockers, and are not associated with QTc prolongation


1c contains our pill-in-the-pockets flecainide and propafenone. Class 1c antiarrythmics have the most potent sodium channel blockade and widen the QRS interval most compared to the other classes. They significantly prolong the cardiac action potential.


You can recall them easier by keeping it simple and start with 4. Procainamide and lidocaine are the only IV formulations. Be lidocaine without QTc prolongation. C has pill-in-the-pockets flecanide and propafenone.


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References

  1. Lei M, Terrar D, Huang C. Modernized Classification of Cardiac Antiarrythmic Drugs. Circulation. 2018;138:1879–1896.

  2. Huang C, Wu L, Jeevaratam K, Lei M. Update on antiarrhythmic drug pharmacology. J Cardiovasc Electrophysiol. 2020 Feb;31(2):579-592.

  3. Kowey P. Pharmacological effects of antiarrhythmic drugs. Review and update. Arch Intern Med. 1998 Feb 23;158(4):325-32.









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