Lidocaine


Lidocaine, also known as lignocaine, is a medication used to numb tissue in a specific area. It is also used to treat ventricular tachycardia and to perform nerve blocks. Lidocaine mixed with a small amount of adrenaline is available to allow larger doses for numbing, to decrease bleeding, and to make the numbing effect last longer. When used as an injectable, lidocaine typically begins working within four minutes and lasts for half an hour to three hours. Lidocaine mixtures may also be applied directly to the skin or mucous membranes to numb the area.
Common side effects with intravenous use include sleepiness, muscle twitching, confusion, changes in vision, numbness, tingling, and vomiting. It can cause low blood pressure and an irregular heart rate. There are concerns that injecting it into a joint can cause problems with the cartilage. It appears to be generally safe for use in pregnancy. A lower dose may be required in those with liver problems. It is generally safe to use in those allergic to tetracaine or benzocaine. Lidocaine is an antiarrhythmic medication of the class Ib type. This means it works by blocking sodium channels and thus decreasing the rate of contractions of the heart. When it is used locally as a numbing agent, local neurons cannot signal the brain.
Lidocaine was discovered in 1946 and went on sale in 1948. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. It is sold under a number of brand names including Xylocaine. In 2017, it was the 208th most commonly prescribed medication in the United States, with more than two million prescriptions.

Medical uses

Local numbing agent

The efficacy profile of lidocaine as a local anaesthetic is characterized by a rapid onset of action and intermediate duration of efficacy. Therefore, lidocaine is suitable for infiltration, block, and surface anaesthesia. Longer-acting substances such as bupivacaine are sometimes given preference for spinal and epidural anaesthesias; lidocaine, though, has the advantage of a rapid onset of action. Adrenaline vasoconstricts arteries, reducing bleeding and also delaying the resorption of lidocaine, almost doubling the duration of anaesthesia.
Lidocaine is one of the most commonly used local anaesthetics in dentistry. It can be administered in multiple ways, most often as a nerve block or infiltration, depending on the type of treatment carried out and the area of the mouth worked on.
For surface anaesthesia, several formulations can be used for endoscopies, before intubations, etc. Buffering the pH of lidocaine makes local numbing less painful. Lidocaine drops can be used on the eyes for short ophthalmic procedures. There is tentative evidence for topical lidocaine for neuropathic pain and skin graft donor site pain. As a local numbing agent, it is used for the treatment of premature ejaculation.
An adhesive transdermal patch containing a 5% concentration of lidocaine in a hydrogel bandage, is approved by the US FDA for reducing nerve pain caused by shingles. The transdermal patch is also used for pain from other causes, such as compressed nerves and persistent nerve pain after some surgeries.

Heart arrhythmia

Lidocaine is also the most important class-1b antiarrhythmic drug; it is used intravenously for the treatment of ventricular arrhythmias if amiodarone is not available or contraindicated. Lidocaine should be given for this indication after defibrillation, CPR, and vasopressors have been initiated. A routine preventative dose is no longer recommended after a myocardial infarction as the overall benefit is not convincing.

Epilepsy

A 2013 review on treatment for neonatal seizures recommended intravenous lidocaine as a second-line treatment, if phenobarbital fails to stop seizures.

Other

Intravenous lidocaine infusions are also used to treat chronic pain and acute surgical pain as an opiate sparing technique. The quality of evidence for this use is poor so it is difficult to compare it to placebo or an epidural.
Inhaled lidocaine can be used as a cough suppressor acting peripherally to reduce the cough reflex. This application can be implemented as a safety and comfort measure for patients who have to be intubated, as it reduces the incidence of coughing and any tracheal damage it might cause when emerging from anaesthesia.
Lidocaine, along with ethanol, ammonia, and acetic acid, may also help in treating jellyfish stings, both numbing the affected area and preventing further nematocyst discharge.
For gastritis, drinking a viscous lidocaine formulation may help with the pain.

Adverse effects

s are rare when lidocaine is used as a local anesthetic and is administered correctly. Most ADRs associated with lidocaine for anesthesia relate to administration technique or pharmacological effects of anesthesia, and allergic reactions only rarely occur. Systemic exposure to excessive quantities of lidocaine mainly result in central nervous system and cardiovascular effects – CNS effects usually occur at lower blood plasma concentrations and additional cardiovascular effects present at higher concentrations, though cardiovascular collapse may also occur with low concentrations. ADRs by system are:
ADRs associated with the use of intravenous lidocaine are similar to toxic effects from systemic exposure above. These are dose-related and more frequent at high infusion rates. Common ADRs include: headache, dizziness, drowsiness, confusion, visual disturbances, tinnitus, tremor, and/or paraesthesia. Infrequent ADRs associated with the use of lidocaine include: hypotension, bradycardia, arrhythmias, cardiac arrest, muscle twitching, seizures, coma, and/or respiratory depression.
It is generally safe to use lidocaine with vasoconstrictor such as adrenaline, including in regions such as the nose, ears, fingers, and toes. While concerns of tissue death if used in these areas have been raised, evidence does not support these concerns.

Interactions

Any drugs that are also ligands of CYP3A4 and CYP1A2 can potentially increase serum levels and potential for toxicity or decrease serum levels and the efficacy, depending on whether they induce or inhibit the enzymes, respectively. Drugs that may increase the chance of methemoglobinemia should also be considered carefully. Dronedarone and liposomal morphine are both absolutely a contraindication, as they may increase the serum levels, but hundreds of other drugs require monitoring for interaction.

Contraindications

Absolute contraindications for the use of lidocaine include:
Exercise caution in patients with any of these:
Overdoses of lidocaine may result from excessive administration by topical or parenteral routes, accidental oral ingestion of topical preparations by children, accidental intravenous injection, or from prolonged use of subcutaneous infiltration anesthesia during cosmetic surgery.
Such overdoses have often led to severe toxicity or death in both children and adults. Lidocaine and its two major metabolites may be quantified in blood, plasma, or serum to confirm the diagnosis in potential poisoning victims or to assist forensic investigation in a case of fatal overdose.
Lidocaine is often given intravenously as an antiarrhythmic agent in critical cardiac-care situations. Treatment with intravenous lipid emulsions to reverse the effects of local anaesthetic toxicity is becoming more common.

Postarthroscopic glenohumeral chondrolysis

Lidocaine in large amounts may be toxic to cartilage and intra-articular infusions can lead to postarthroscopic glenohumeral chondrolysis.

Pharmacology

Mechanism of action

Lidocaine alters signal conduction in neurons by prolonging the inactivation of the fast voltage-gated Na+ channels in the neuronal cell membrane responsible for action potential propagation. With sufficient blockage, the voltage-gated sodium channels will not open and an action potential will not be generated. Careful titration allows for a high degree of selectivity in the blockage of sensory neurons, whereas higher concentrations also affect other types of neurons.
The same principle applies for this drug's actions in the heart. Blocking sodium channels in the conduction system, as well as the muscle cells of the heart, raises the depolarization threshold, making the heart less likely to initiate or conduct early action potentials that may cause an arrhythmia.

Pharmacokinetics

When used as an injectable it typically begins working within four minutes and lasts for half an hour to three hours. Lidocaine is about 95% metabolized in the liver mainly by CYP3A4 to the pharmacologically active metabolites monoethylglycinexylidide and then subsequently to the inactive glycine xylidide. MEGX has a longer half-life than lidocaine, but also is a less potent sodium channel blocker. The volume of distribution is 1.1 L/kg to 2.1 L/kg, but congestive heart failure can decrease it. About 60% to 80% circulates bound to the protein alpha1 acid glycoprotein. The oral bioavailability is 35% and the topical bioavailability is 3%.
The elimination half-life of lidocaine is biphasic and around 90 min to 120 min in most patients. This may be prolonged in patients with hepatic impairment or congestive heart failure. Lidocaine is excreted in the urine.

History

Lidocaine, the first amino amide–type local anesthetic, was first synthesized under the name 'xylocaine' by Swedish chemist Nils Löfgren in 1943. His colleague Bengt Lundqvist performed the first injection anesthesia experiments on himself. It was first marketed in 1949.

Society and culture

Dosage forms

Lidocaine, usually in the form of its hydrochloride salt, is available in various forms including many topical formulations and solutions for injection or infusion. It is also available as a transdermal patch, which is applied directly to the skin.

Cost

The wholesale cost in the developing world in 2014 was to $1.05 wholesale per 20 ml vial of medication.

Names

Lidocaine is the International Nonproprietary Name, British Approved Name, and Australian Approved Name, while lignocaine is the former BAN and AAN. Both the old and new names will be displayed on the product label in Australia until at least 2023.
Xylocaine is a brand name.

Recreational use

Lidocaine is not currently listed by the World Anti-Doping Agency as an illegal substance. It is used as an adjuvant, adulterant, and diluent to street drugs such as cocaine and heroin. It is one of the three common ingredients in site enhancement oil used by bodybuilders.

Adulterant in cocaine

Lidocaine is often added to cocaine as a diluent. Cocaine and lidocaine both numb the gums when applied. This gives the user the impression of high-quality cocaine, when in actuality the user is receiving a diluted product.

Compendial status

It is a component of the veterinary drug Tributame along with embutramide and chloroquine used to carry out euthanasia on horses and dogs.