Sodium Channel Blockers: Drug List, Examples, Mechanism of Action
Sodium Channel Blockers: Drug uses as class I antiarrhythmics, list of example medications, and mechanism of action explained! Includes memory tricks for nursing and pharmacology!
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Sodium Channel Blockers
What are Sodium Channel Blockers?
Sodium channel blockers are drugs used to treat conditions such as:
Cardiac arrhythmias
Seizures or epilepsy
Neuropathic (nerve) pain
Other uses: anesthetics
How do Sodium Channel Blockers work? (Mechanism of Action)
Sodium channel blockers are medications that block voltage-gated sodium channels in cell membranes
This slows the rapid influx of sodium ions into cells that cause an action potential
Electrical impulses (action potentials) in cells are slowed as a result
How are Sodium Channel Blockers Used?
Sodium channel blockers are primarily used as:
Antiarrhythmic drugs (class I)
Anesthetics
Antiseizure medications
Memory Trick!
This lecture focuses on sodium channel blockers used as antiarrhythmic drugs to treat abnormal heart rhythms.
You will learn several memory tricks to remember the:
Mechanism of Action
Subclasses
Example drugs
And more!
Comment below if this lecture was useful!
Sodium Channel Blockers: The mechanism of action involves blocking sodium channels in heart muscle cells (phase 0) to treat abnormal heart rhythms (antiarrhythmic).
Cardiac Action Potential (Sodium Channels)
Sodium channel blockers can be used as antiarrhythmic drugs (class I) to treat abnormal heart rhythms.
They function as antiarrhythmics by targeting the action potentials of cardiac cells.
Let’s briefly review cardiac action potentials, as this will help you understand sodium channel blockers and how they work.
We learned in the cardiac action potential lecture that sodium channels are present in non-pacemaker cardiac cells (i.e. atrial and ventricular myocytes).
As the voltage across the cell membrane becomes more positive from an external stimulus, sodium channels open once a threshold voltage is met.
Sodium ions enter the cell, resulting in a rapid increase in voltage across the cell membrane.
This is referred to as depolarization, which is phase 0 of the action potential.
Depolarization will ultimately lead to contraction of the atria and ventricles.
Recap: Phase 0 involves an influx of sodium ions across the cell membrane, leading to depolarization (the “summit” phase of the action potential).
We also learned that sodium channels are less involved in pacemaker cells, which primarily use calcium for depolarization and potassium for repolarization.
For more information and the memory tricks about cardiac action potentials, please visit our lecture below:
Cardiac Action Potentials: Phase 0 of non-pacemaker cells involves an influx of sodium, and is a primary target for sodium channel blockers (class I antiarrhythmics).
Sodium Channel Blocker - Mechanism of Action
Now that we understand the sodium channel involvement in generating an action potential, let’s discuss how sodium channel blockers work.
Sodium channel blockers are class I antiarrhythmic drugs.
The other classes of antiarrhythmics are:
Beta Blockers (class II)
Potassium Channel Blockers (class III)
Calcium Channel Blockers (class IV)
As the name suggests, sodium channel blockers block sodium channels.
What part of the action potential did we say sodium is involved? (see above)
Sodium channels are involved in the “summit” phase (phase 0) of non-pacemaker cells, in which an influx of sodium leads to depolarization of the cell.
Sodium channel blockers slow the entry of sodium into the cell.
As a result, the cell has a harder time becoming more positive and depolarizing.
This will decrease the slope of phase 0, and the depolarization rate and amplitude will be reduced resulting in:
Decreased cardiac conduction velocity
Decreased cardiac cell transmission
Decreased atrial and ventricular myocyte excitability
The above actions help to suppress abnormal conduction rhythms (antiarrhythmic).
Note: There are different subclasses of sodium channel blockers (see below).
The different subclasses of sodium channel blockers have varying effects on slowing the slope of phase 0:
Class IA - moderate
Class IB - weak
Class IC - strong
Since pacemaker cells use calcium ions to depolarize (see above), sodium channel blockers have little effect on the SA node and AV node (pacemaker cells).
For this reason, sodium channel blockers are useful in re-entry tachyarrhythmias where blocking the AV node could be detrimental.
Sodium Channel Blockers: The mechanism of action involves blocking sodium channels in heart muscle cells, which slows the influx of sodium and decreases the slope of phase 0 (red line).
Sodium Channel Blocker - Subclasses
As previously mentioned, sodium channel blockers are class I antiarrhythmics.
They can then be subdivided further into 3 subclasses:
Class IA
Class IB
Class IC
The subclasses are defined by their effects on repolarization.
Note: The above subclasses primarily apply to class I antiarrhythmic drugs targeting cardiac sodium channels.
The subclasses do not apply to other sodium channel blockers such as local anesthetics, antiseizure medications, etc.
Memory Trick
Each subclass of sodium channel blockers, and their effect on repolarization, can be remembered using the following memory trick:
Class IA = After
Repolarization occurs after the normal repolarization phase
Class IB = Before
Repolarization occurs before the normal repolarization phase
Class IC = Correct
Repolarization occurs correctly with the normal repolarization phase
Let’s discuss each subclass below.
Sodium Channel Blockers: The classes of sodium channel blockers and their mechanism of action can be remembered using the memory trick: A = After; B = Before; C = Correct
Class IA Sodium Channel Blockers
Class IA sodium channel blockers prolong the repolarization phase leading to an increase in action potential duration and effective refractory period.
Class IA sodium channel blockers have a moderate effect on slowing the slope of phase 0.
Memory Trick:
The way to remember Class IA sodium channel blockers is:
A = After
Meaning class IA repolarization occurs after the normal repolarization phase.
Example Class IA medications include:
Procainamide
Quinidine
Disopyramide
Class IA Sodium Channel Blockers: List of example medications and mechanism of action on depolarization (phase 0 - red) and repolarization (phase 3 - purple) of action potential.
Class IB Sodium Channel Blockers
Class IB sodium channel blockers shorten the repolarization phase leading to a decrease in action potential duration and effective refractory period.
Class IB sodium channel blockers have a weak effect on slowing the slope of phase 0.
Memory Trick:
The way to remember Class IB sodium channel blockers is:
B = Before
Meaning class IB repolarization occurs before the normal repolarization phase.
Example Class IB medications include:
Lidocaine
Tocainide
Phenytoin
Mexiletine
Class IB Sodium Channel Blockers: Example drug list and mechanism of action on depolarization (phase 0 - red) and repolarization (phase 3 - purple) of action potential.
Class IC Sodium Channel Blockers
Class IC sodium channel blockers have no effect on repolarization, action potential duration, or effective refractory period.
Class IC sodium channel blockers have a strong effect on slowing the slope of phase 0.
Memory Trick:
The way to remember Class IC sodium channel blockers is:
C = Correct
Meaning class IC repolarization occurs correctly with the normal repolarization phase (repolarization occurs as normal).
Example Class IC medications include:
Flecainide
Propafenone
Class IC Sodium Channel Blockers: Example medication list and mechanism of action on depolarization (phase 0 - red) and repolarization (phase 3 - purple) of action potential.
Sodium Channel Blockers - Examples
Below is a quick and fun memory trick to remember the different sodium channel blockers and their classes!
Memory Trick!
Use the mnemonic “Double Quarter Pounder, Lettuce Tomato Pickle May, Fries Please”
Class 1A = “Double Quarter Pounder”
Disopyramide
Quinidine
Procainamide
Bonus: Procainamide commonly appears on medical tests and licensure exams, especially for the treatment of Wolff-Parkinson-White syndrome (WPW).
Class IB = “Lettuce Tomato Pickle Mayo”
Lidocaine
Tocainide
Phenytoin
Mexiletine
Bonus: Lidocaine and phenytoin are more common, and they are typically the class IB medications tested on exams.
Class IC = “Fries Please”
Flecainide
Propafenone
Bonus: Flecainide is more common and is typically the Class IC medication tested on exams.
The above mnemonic is widely used and found in various resources.
Sodium Channel Blockers: List of example medications for each subclass with a memory trick to remember the drug names.
Practical Applications
EKG
As discussed above, sodium channel blockers decrease the slope of phase 0 of non-pacemaker cell action potentials (i.e. atrial and ventricular myocytes).
This will decrease the depolarization rate and amplitude.
Let’s now correlate this with an EKG.
The QRS interval reflects ventricular depolarization
Therefore, sodium channel blockers can prolong or widen the QRS interval.
Sodium Channel Blocker Toxicity
The above EKG findings are important in cases of sodium channel blocker toxicity or overdose, in which the QRS can widen and lead to dysrhythmias.
Summary
Hopefully this lecture helped you understand sodium channel blockers and their mechanism of action on action potentials.
Using the above memory tricks can help you remember the different subclasses of medications and their effects on repolarization.
A, B, C = After, Before, Correct in relation to the repolarization phase.
The above memory tricks can also help with the different medications in each sodium channel blocker subclass.
“Double Quarter Pounder, Lettuce Tomato Pickle Mayo, Fries Please”
Last updated 12/12/2025