Sodium Channel Blockers

Sodium channel blockers include:

  • Class Ia:
    • Procainamide
    • Quinidine
    • Disopyramide
  • Class Ib:
    • Lignocaine
    • Mexiletine (lignocaine analogue)
  • Class Ic:
    • Flecainide

In general:

  • IV preparations are given for VT
  • Good PO bioavailability and low protein binding
  • Metabolites are renally cleared
Property Procainamide Lignocaine Flecainide
Class Class Ia amide Class Ib amide local anaesthetic Class Ic amide local anaesthetic
Uses SVT/VT VT SVT/VT
Presentation Clear solution at 10-20mg.ml-1 (1-2%)
Route of Administration PO/IV IV PO/IV
Dosing 100mg IV load, followed by infusion at 2-6mg.ml-1 Load at 1mg.kg-1 followed by infusion at 1-3mg.min-1 2mg.kg-1 (up to 150mg) load over 10-30 minutes, followed by infusion at 1.5mg.kg-1.hr-1, aiming for levels of <0.9mg/ml
Absorption 75% bioavailability IV only for arrhythmia 90% orally bioavailable
Distribution 33% unionised, 70% protein bound 50% protein bound
Metabolism Hepatic to active metabolites via acetylation - slow acetylators at increased risk of side effects Hepatic amidases to inactive metabolites Hepatic to active metabolites
Mechanism of Action Reduces the rate of rise of phase 0, raises the threshold potential, and prolongs the refractory period without prolonging the action potential Reduces the rate of rise of phase 0 of the action potential. Repolarisation phase is shortened. Reduces the rate of rise of phase 0 0of the action potential. Repolarisation is unchanged.
CVS HR, ↓SVR, ↓BP, ↓CO, heart block, may ↑HR when used for SVT, ↑QT with risk of TDP AV block, myocardial depression causing unresponsive ↓BP Precipitate pre-existing conduction disorders, ↓ inotropy, ↑ pacing and defibrillation threshold
CNS Circumoral tingling, dizziness, parasthesia, confusion, seizures, coma Dizziness, parasthesia, headache
Immune Lupoid syndrome in 20-30%, reduces antimicrobial effect of sulfonamides
Interactions Pharmacokinetic interactions with digoxin, propranolol, amiodarone

References

  1. Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
  2. Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.
Last updated 2017-10-08

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