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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Local anesthetics

Drugs that block nerve sodium channels and numb an area without loss of consciousness: stitches, dentistry, nerve blocks and spinal anesthesia.

Updated 2026-11-01

## What they are

They reversibly block nerve conduction where they are applied. By their intermediate link they split into amides (lidocaine, bupivacaine) and esters (procaine, benzocaine).

## Mechanism of action

They are weak bases: the uncharged form crosses the axon membrane and, once inside, the charged form blocks the pore of the voltage-gated sodium channel from the inner side. They bind best to open or inactivated channels, so they block fibers that fire often more strongly. Without sodium entry no action potential is generated and the pain signal never reaches the brain.

Target: Voltage-gated sodium channels (Nav)

## Key points

- Amides are metabolized in the liver; esters by plasma cholinesterase, which yields PABA, the cause of most allergies.
- In acidic, infected tissue more drug stays ionized outside the nerve, less gets in and the block weakens.
- Thin fibers (pain and temperature) are blocked first and thick motor fibers last.
- Systemic toxicity starts with perioral numbness, tinnitus and a metallic taste, moves to seizures and ends in cardiovascular collapse; it is treated with lipid emulsion.
- Bupivacaine is the most cardiotoxic; prilocaine and benzocaine can cause methemoglobinemia.

## Drugs in this class

- [**Lidocaine** The most used local anesthetic: it numbs skin and nerves by blocking sodium channels. It is also a class Ib… Voltage-gated sodium channel (Nav; in the heart, Nav1.5)](https://durgical.com/en/pharmacology/lidocaine/)
- [**Bupivacaine** Long-acting amide local anaesthetic for epidurals, spinals and nerve blocks. It is the most cardiotoxic of its group. Voltage-gated sodium channels (Nav)](https://durgical.com/en/pharmacology/bupivacaine/)
- [**Ropivacaine** Long-acting amide local anaesthetic, related to bupivacaine but less cardiotoxic. Used for epidurals, nerve blocks and… Voltage-gated sodium channels (Nav)](https://durgical.com/en/pharmacology/ropivacaine/)
- [**Tetracaine** Potent, long-acting ester local anaesthetic: eye drops for ocular procedures and an option for spinal anaesthesia. Voltage-gated sodium channels (Nav)](https://durgical.com/en/pharmacology/tetracaine/)
- [**Cocaine** The only local anaesthetic that constricts vessels: a nasal solution for nose surgery. It raises blood pressure, can… Monoamine transporters (dopamine and noradrenaline transporters) and sodium channels](https://durgical.com/en/pharmacology/cocaine/)
- [**Benzocaine** Topical ester local anaesthetic in gels, sprays and lozenges for the mouth and throat. It can cause methaemoglobinaemia. Voltage-gated sodium channels (Nav)](https://durgical.com/en/pharmacology/benzocaine/)
- [**Procaine** The classic ester local anaesthetic: low potency and short-acting. Today it is used mainly as part of procaine… Voltage-gated sodium channels (Nav)](https://durgical.com/en/pharmacology/procaine/)

## Others in the class

- bupivacaine
- ropivacaine
- mepivacaine
- prilocaine
- procaine
- tetracaine
- benzocaine

## Test yourself

Think of the answer, then tap the question to see it.

## Why does a local anesthetic work poorly in an abscess?

The acidic pH raises the ionized fraction of the drug outside the nerve; that charged form crosses the axon membrane poorly, so less reaches its site of action.

## Which drug is used for severe local anesthetic systemic toxicity?

Intravenous lipid emulsion, alongside airway support, seizure control and resuscitation.

## Why is true allergy more common with ester-type local anesthetics?

Their hydrolysis by plasma cholinesterase produces para-aminobenzoic acid (PABA), a known allergen.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Anesthesia: MedlinePlus](https://medlineplus.gov/anesthesia.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [Lidocaine Transdermal Patch: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a603026.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

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