What is the primary mechanism of lidocaine?

• A. Blocks potassium channels
• B. Inhibits calcium channels
• C. Enhances sodium channel activity
• D. Blocks sodium channels to stop action potentials

Answer: (D)

Lidocaine works by blocking voltage-gated sodium channels. By binding to these channels from inside the cell when they are open or inactivated, it prevents the sodium influx that drives the rapid depolarization phase of action potentials. Without this inward current, neurons can’t reach threshold as readily and the upstroke of the action potential slows or stops, so nerve conduction is diminished. This use-dependent block means tissues with higher firing rates or in inflamed/ischemic states are more affected, which is why lidocaine is effective as a local anesthetic and can help suppress certain cardiac arrhythmias. It does not block potassium or calcium channels, nor does it enhance sodium channel activity; it specifically dampens sodium channel function to stop action potentials.