Quick Reference Table

The Class I Concept: Sodium Channel Dissociation

Class I drugs are all Sodium Channel Blockers, but they vary based on how long they "stick" to the receptor:

• Class IA (Intermediate): They stick long enough to slow conduction and also block K+ channels (prolonging the refractory period). Think of them as the "middle ground."
• Class IB (Weak/Fast): These drugs hop on and off the receptor very quickly. They prefer channels that are "open" or "inactivated" for a long time—which is exactly what happens in Ischemic (dying) tissue. This is why Lidocaine is the king of Post-MI arrhythmias.
• Class IC (Strong/Slow): These are the "heavy hitters." They stick to the receptor for a long time. Because they block so strongly without changing the refractory period, they can cause new, deadly arrhythmias in damaged hearts (CAST trial). Only use them in structurally normal hearts!