Lidocaine is a drug in the local anesthetic class that also acts as an antiarrhythmic agent. It belongs to the sodium channel blocker group.
What is lidocaine?
Lidocaine is a drug in the local anesthetic class that also acts as an antiarrhythmic agent. The drug lidocaine was the first amino-amide local anesthetic. It was synthesized in 1943 by Swedish chemists Bengt Lundqvist and Nils Löfgren. They sold their patent rights to the pharmaceutical company Astra AB. The basis of lidocaine is 2,6-xylidine. Lidocaine is produced from this in several synthesis steps. The drug is available as a monopreparation or as a combination preparation in the form of gels, pastes, ointments, suppositories and injection solutions. Injection solutions can be 0.25% or 5%. Lidocaine belongs to the local anesthetics and to the class of sodium channel blockers. However, it is used not only as a local anesthetic but also as an antiarrhythmic agent in medicine. Lidocaine acts very quickly. It is metabolized in the so-called cytochrome 450 system of the liver. Its bioavailability is very good. Less than 10 percent of the original dose is excreted in the urine.
Pharmacologic effects
Lidocaine is a sodium channel blocker. The drug blocks voltage-gated channels for sodium. These are located in the cell membranes of nerve cells. When a nerve cell is excited, sodium flows into the cells. An action potential is generated and the excitation is transmitted from one nerve cell to the next or from one nerve cell to the target cell by depolarization processes. When the sensitive receptors of the skin perceive sensations such as pressure, pain, heat or cold, they transmit these sensations to the brain. This requires excitation propagation and thus also an opening of the sodium channels in the cell membranes. Lidocaine blocks the sodium channels so that no sodium can flow into the cells. The formation of an action potential is impeded, and the stimulus is not transmitted. At the same time, lidocaine has only a local effect. Only the nerve cells located at the site of application of the drug are affected. Thin nerve fibers are blocked more quickly in their transmission function than thick nerve fibers. After application, the sensation of pain is initially reduced. Subsequently, temperatures are no longer perceived. Then touch and pressure sensations deteriorate. Finally, the efferents fail. Efferents are nerve fibers that run from the central nervous system to the muscles. When the efferents fail, motor function also fails in the affected area.
Medical application and use
The main use of lidocaine is regional anesthesia. Local anesthesia eliminates the sensation of pain in a limited area of the body. The advantage over general anesthesia is that lung and brain function, metabolism, and even acid-base balance are hardly affected. Lidocaine is frequently administered as a local anesthetic in dental and medical treatment. It is used for surface anesthesia, conduction anesthesia, and infiltration anesthesia. In infiltration anesthesia, lidocaine is injected into tissue to numb a small area. This may be necessary, for example, when suturing a laceration or similar minor procedures. Alternatively, lidocaine may be injected near a nerve. This numbs the area supplying the nerve. This procedure is also known as conduction anesthesia. After a contact time of one to three minutes, the local anesthesia lasts for one to three hours. Lidocaine is also well absorbed through the mucous membranes. In the form of sprays or ointments, the active ingredient is therefore used for surface anesthesia. Surface anesthesia guarantees freedom from pain, for example, in the treatment of hemorrhoids or during endoscopies. Lidocaine is also available in the form of so-called delay creams or delay spray solutions. These are applied thinly to the glans of the penis when the foreskin is retracted to suppress premature ejaculation. Lidocaine is also used as an active ingredient in teething aids as a local anesthetic. The second major area of application for the drug is cardiac arrhythmias. Lidocaine slows down the spread of excitation in the cardiac conduction system. The drug thus has a stabilizing effect on the heart rhythm and suppresses cardiac arrhythmias originating in the ventricles.Thus, lidocaine is predominantly used for the treatment of tachycardic arrhythmias. In the past, lidocaine was used very frequently as an emergency medication. However, its use has now declined because lidocaine can not only prevent cardiac arrhythmias but also produce them in individual cases. In its function as an antiarrhythmic agent, lidocaine must be administered intravenously. Indications for intravenous administration of lidocaine are cardiac arrhythmias of any etiology. This also includes cardiac arrhythmias caused by poisoning with antidepressants or cardiac glycosides. Lidocaine can be administered as a preventive measure before interventions that may irritate the heart muscle. It reduces the risk of ventricular arrhythmias.
Risks and side effects
Side effects are uncommon with low doses of lidocaine. If the dosage is too high, cardiac adverse effects and systemic adverse effects may occur. These include symptoms such as drowsiness, restlessness, convulsions, and negative inotropy of the heart. In negative inotropy, the contractile force of the heart is reduced. In individual cases, a drop in blood pressure or allergic reactions may also occur. Very rarely, patients fall into a coma after high doses of lidocaine.
