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 and 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 of 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
- Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
- Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.