Local Anesthetic

Lidocaine

An amide local anesthetic used by injection, gel, ointment or spray, and given IV as a class Ib antiarrhythmic.

Also called lignocaine (former UK name).

Drug card

Class: Local anesthetic
How it works: Blocking voltage-gated sodium channels so nerves cannot fire impulses
Used for: Local and regional anesthesia by injection
Numbing the mouth, throat and skin (gel, ointment)
Ventricular arrhythmias, such as in a heart attack (IV)
Pain of minor burns, grazes and insect bites
Known for: Seizures at high blood levels
Arrhythmias and cardiac arrest
Its name: -caine means a local anesthetic

Study it as a flashcard, and it comes back before you forget it.

Mechanism of action

How does lidocaine work?

Lidocaine binds voltage-gated sodium channels and stabilizes the nerve membrane, so impulses cannot start or spread. In the heart it raises the ventricle's diastolic threshold for electrical stimulation, suppressing ventricular arrhythmias. The liver clears it via CYP1A2 and CYP3A4 to weaker active metabolites (MEGX, GX); its IV half-life is about 1.5 to 2 hours.

Like other local anesthetics: Local anesthetics bind voltage-gated sodium channels in nerve membranes, so the action potential rises slowly or not at all and impulses stop. Fiber size and myelination set the order of block: pain goes first, then temperature, touch and position sense, and muscle tone last. Lidocaine and bupivacaine are amides, broken down by the liver; epinephrine is often added to slow absorption and lengthen the block.

Uses

What is lidocaine used for?

Local and regional anesthesia by injection
Numbing the mouth, throat and skin (gel, ointment)
Ventricular arrhythmias, such as in a heart attack (IV)
Pain of minor burns, grazes and insect bites

Side effects

Side effects of lidocaine

Seizures at high blood levelsKnown forSerious
Arrhythmias and cardiac arrestKnown forSerious
Lightheadedness, dizziness and drowsiness
Tinnitus and blurred or double vision
Tremor and twitching
Confusion and euphoria
Breathing depression and arrestSerious
Slow heart rateSerious
Low blood pressure
Nausea and vomiting
MethemoglobinemiaSerious
Allergic reactions, including anaphylaxis (rare)Serious

Known for marks what an exam expects you to know it for.

Watch for

Cautions and what sets it apart

Aspirate before injecting: an accidental intravascular dose can cause seizures and cardiac arrest.
IV use needs continuous ECG monitoring; it is contraindicated in WPW syndrome and severe SA, AV or intraventricular block.
Liver or kidney impairment raises the risk of toxicity.
Methemoglobinemia is likelier in G6PD deficiency, infants under 6 months and with other oxidizing drugs.

Good to know: One drug, two jobs: a local anesthetic, and, given IV, a class Ib antiarrhythmic for ventricular arrhythmias. The UK formerly called it lignocaine.

Remember it

A way to remember it

Pain leaves first, muscle power last.

Local anesthetics block nerve fibers in an order set by their size and myelination, so sensation goes in turn: pain, temperature, touch, position sense, and finally muscle tone.

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Its name

-caine means local anesthetic
Lidocaine and bupivacaine block sodium channels in nerves. Inside a name, -cain- marks class I antiarrhythmics such as flecainide and procainamide; lidocaine treats arrhythmias too.
Every drug name stem

Its class

Local anesthetics

Other local anesthetics with a card:

Bupivacaine

Easily mixed up with sodium channel-blocking antiepileptics, class III antiarrhythmics and intravenous anesthetics.

All about local anesthetics

Sources

Checked against

Written for biofideX in plain words, after checking these references:

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.

Practice it

Anesthesia and muscle relaxants

Lidocaine is one of 8 drugs practiced together here: their classes, how they work, what they treat and what they're known for.

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