Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia. When used for local anaesthesia or in nerve blocks, lidocaine typically begins working within several 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. It is often used mixed with a small amount of adrenaline (epinephrine) to prolong its local effects and to decrease bleeding.
If injected intravenously, it may cause cerebral effects such as 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 injected near nerves, the nerves cannot conduct signals to or from 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. In 2020, it was the 337th most commonly prescribed medication in the United States, with more than 700thousand prescriptions.
Molecular Structure and Conformational Flexibility
At the heart of lidocaine's molecular structure lies a lipophilic group featuring a 1,5-dimethylbenzene core, contributing to the molecule's hydrophobic characteristics. In addition to this aromatic unit, lidocaine incorporates an aliphatic section comprising amide, carbonyl, and enyl groups. This multifaceted arrangement endows the molecule with unique properties and a capacity to interact with biological systems.
Lidocaine exhibits a remarkable degree of conformational flexibility, resulting in more than 60 probable conformers. This adaptability arises from the high lability of the amide and ethyl groups within the molecule. These groups can undergo shifts in their positions, leading to significant variations in the overall molecular configuration.
Influence of Temperature and Pressure on conformational preference
The dynamic transformation of lidocaine conformers in supercritical carbon dioxide (scCO2) highly depends on external factors such as pressure and temperature. Alterations in these conditions can lead to distinct conformations, impacting the molecule's physicochemical properties. One notable consequence of these variations is the particle size of lidocaine when produced through micronization using scCO2. Changes in the position of the amide group within the molecule can trigger a redistribution of intra- and intermolecular hydrogen bonds, affecting the outcome of the micronization process and the resultant particle size/
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. 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.