LIDOCAINE: MECHANISM OF ACTION, WHAT IT IS FOR - MEDICINE - 2025

The lidocaine is a drug used to produce local anesthesia or nerve blocks truncal. Its main effect is the reduction or blocking of pain sensitivity, in addition to having an effect on the contractile activity of the myocardium. The drug is useful for surgical procedures, an adjunct to analgesia, and an antiarrhythmic drug.

In the early nineteenth century, cocaine was used as an anesthetic. In 1904, the first cocaine derivative appeared - procaine - used in the first decades of the century. Lidocaine is a derivative of procaine that was used for the first time during World War II, in 1943. That same year it had been synthesized by the Swiss chemist Nils Lofgren.

Chemically, lidocaine is an amino-amide, a small molecule, and its presentation is as lidocaine hydrochloride. The effect of lidocaine is short compared to other anesthetics such as bupivacaine and mepivacaine. Its action begins before 2 minutes and its effect lasts from 30 to 60 minutes.

Today, lidocaine is considered a necessary, effective and safe drug. It is included in the WHO essential medicines list, it is widely used and accessible.

Anesthetics are an essential tool to reduce patient discomfort and pain when performing surgical procedures.

Mechanism of action

The pain receptors -nociceptors- are located in practically the entire body; They are sensory endings that transmit pain sensitivity to the afferent nerve fibers responsible for carrying information to the central nervous system. The nerve impulse occurs due to changes in the action potential of the sensory fibers.

Depolarization at the level of nerve fibers is dependent on ion exchange at the membrane level. Sodium, the main extracellular cation, must enter the nerve cell to trigger the nerve impulse. This passage of sodium is carried out through specialized membrane ion channels, producing a change in potential.

The mechanism of action of lidocaine is relatively simple. The anesthetic diffuses and reaches the neuronal axons, stabilizing the membrane and preventing depolarization; This occurs by inhibiting the entry of sodium into the cell by blocking ion channels. Depolarization and transmission of pain to the nervous system does not occur in this case.

As for the heart, lidocaine causes a decrease in heart rate; myocardial muscle contraction occurs due to sodium entry into the myocyte, which promotes muscle fiber contractility. The blockage of ion channels produces a decrease in the frequency of contractions as sodium does not enter the cell.

The combination of adrenaline with the anesthetic is frequent. Epinephrine causes closure of the capillaries, preventing the passage of lidocaine into the bloodstream.

Consequently, the anesthetic effect is prolonged by the permanence of the drug at the injection site. Its utility is in infiltrative anesthesia for extensive surgical procedures.

What is it for?

The uses of lidocaine are multiple due to its characteristics. A rapid onset of action, relatively short effect, and few adverse effects allow it to be used in a large number of medical procedures. It is used in local anesthesia -topic and infiltrative-, regional blockade and as an antiarrhythmic, among other uses.

Local anesthesia

Lidocaine may come as a solution for injection, a spray, topical gel or cream preparations, and as patches. These presentations allow it to be used on mucosa, skin and local infiltration for minor surgery.

Local anesthesia does not require combination with other drugs, except for adrenaline for dental use. Its common uses are:

- Minor surgery.

- Surgical techniques such as placement of urinary or nasogastric tubes.

- Infiltration to place central line catheters.

- Relief of pain caused by trauma and wounds.

- Dental procedures such as dental extraction or repair.

- Endoscopic procedures: gastroscopy, colonoscopy, bronchofibroscopy.

- Intra-articular infiltration is used in inflammatory processes at this level. It is usually combined with long-acting anesthetics and steroidal anti-inflammatory drugs. In some countries, intra-articular use is contraindicated.

- In obstetrics it is applied to perform the episiotomy and widen the birth canal.

Regional blockade

Regional anesthesia involves the use of anesthetic drugs on nerve trunks. The goal of this technique is to block pain over a large area.

Combination with other anesthetics, such as bupivacaine, in addition to adrenaline is usually necessary. It is often used in brachial plexus block.

Spinal and epiridural anesthesia

It is a type of regional anesthesia that involves the injection of lidocaine and bupivacaine, either outside the membranes that line the spinal cord or directly inside the spinal canal. It must be performed by an anesthesiologist and its use is intended for elective or uncomplicated surgeries:

- Appendectomy.

- Caesarean section.

- Varicocele cure.

- Inguinal hernioplasty.

- Lower limb surgery.

- Prostatectomy.

Antiarrhythmic

The inhibitory effect of ventricular excitability makes lidocaine a useful drug as an antiarrhythmic. In adequate doses, it acts by blocking sodium channels - without affecting the activity of the atrial node - thereby reducing the heart rate without other effects. Lidocaine in high doses can cause depression of the circulatory system.

Lidocaine is a class 1b antiarrhythmic. It is a substitute for other antiarrhythmics, such as amiodarone, when they are not available. Its indication intravenously is the treatment of ventricular tachycardia or fibrillation due to multiple causes:

- Cardio-pulmonary resuscitation.

- Arrhythmia after acute myocardial infarction.

- Tachycardia after electrical cardioversion.

- Digitalis intoxication.

- Procedures in hemodynamics, such as catheterization.

Other uses

- Symptomatic relief of reactive or irritative cough. For this, lidocaine is aerosolized with saline for inhalation.

- Its use has been described for recurrent seizures of epilepsy.

Contraindications

Despite the effectiveness and safety that lidocaine provides, some conditions in patients limit or prevent its use. There are both absolute and relative contraindications to the use of this drug.

Absolute contraindications

- Demonstrated hypersensitivity or allergy to lidocaine or its vehicle.

- Heart rhythm disorders that present with blockages, such as sino-atrial block, or 2nd and 3rd atrioventricular blocks.

- Wolf-Parkinson-White and Adam-Stokes syndromes.

- Use of class 1 antiarrhythmics, such as procainamide or quinidine.

- Previous administration of amiodarone.

- Treatments with other drugs such as phenytoin sodium or acetaminophen.

Relative contraindications

- Liver disease or liver failure.

- Hypotension that is not related to arrhythmias.

- Bradycardia.

- Pseudocholinesterase deficiency.

- Porphyria.

- Seniors.

References

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