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Pharmacology · single question

What is the mechanism of action of LOCAL ANESTHETICS (e.g., lidocaine)?

  1. Block voltage-gated sodium (Na⁺) channels, preventing depolarization
  2. Activate GABA receptors to inhibit neuronal firing
  3. Block potassium (K⁺) channels, hyperpolarizing the nerve
  4. Block calcium (Ca²⁺) channels in nerve membranes
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Correct answer: A. Block voltage-gated sodium (Na⁺) channels, preventing depolarization

Local anesthetics (amides: lidocaine, articaine, bupivacaine; esters: benzocaine, procaine) work by blocking voltage-gated sodium channels on the neuronal membrane. They enter the channel from the intracellular side (in their ionized form), physically occluding the channel and preventing Na⁺ influx. Without Na⁺ entry, the action potential cannot be generated or propagated — blocking nerve impulse transmission and causing anesthesia.
  • A. CORRECT. Local anesthetics block voltage-gated Na⁺ channels from the intracellular side, preventing action potential generation and propagation.
  • B. Incorrect. K⁺ channel blockade is the mechanism of some cardiac antiarrhythmics (amiodarone) — not local anesthetics.
  • C. Incorrect. GABA receptor activation is the mechanism of benzodiazepines and barbiturates (sedatives/hypnotics) — not local anesthetics.
  • D. Incorrect. Ca²⁺ channel blockade is the mechanism of calcium channel blockers (antihypertensives like nifedipine, verapamil) — not local anesthetics.

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