Group: local anaesthetic agent
Injection (hydrochloride): 5 mg/ml (0.5%), 10 mg/ml (1%) in 20-ml ampoule; 10 mg/ml (1%) + epinephrine 5 micrograms/ml (1:200 000) in 20-ml ampoule; 20 mg/ml (2%) + epinephrine 12.5 micrograms/ml (1:80 000) in 2.2-ml cartridge for dental anaesthesia; 50 mg/ml (5%) in 2-ml ampoule to be mixed with 75 mg/ml (7.5%) glucose solution
Topical forms: 20-40 mg (hydrochloride)/ml (2-4%) as gel or solution
Lidocaine is a moderately long-acting local anaesthetic. It blocks initiation and transmission of nerve impulses at the site of application by stabilizing the neuronal membrane. The compound is ultimately metabolized in the liver. Anaesthesia, which persists for 1-3 hours, is induced within 1-5 minutes following mucosal application, infiltration and spinal or dental nerve block, and within 10-15 minutes following other methods of administration.
• Surface anaesthesia of mucous membranes.
• Infiltration anaesthesia.
• Peripheral and sympathetic nerve block.
• Dental anaesthesia.
• Spinal anaesthesia.
• Intravenous regional anaesthesia.
• Epidural and caudal anaesthesia (these techniques produce prolonged regional anaesthesia and should be attempted only by experienced specialist anesthetists).
Lidocaine is also the most important class-1b antiarrhythmic drug; it is used intravenously for the treatment of ventricular arrhythmias (for acute myocardial infarction, digoxin poisoning, cardioversion, or cardiac catheterization) 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.
A 2013 review on treatment for neonatal seizures recommended intravenous lidocaine as a second line treatment, if phenobarbital fails to stop seizures.
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.
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.
Dosage and administration
The aim is to administer the smallest effective dose. This varies with the procedure adopted, the degree of anaesthesia required, the rate of absorption from the injection site and the size and responsive-ness of the patient. Higher initial blood levels are attained with more concentrated solutions.
Solutions are available with or without epinephrine at 5 micrograms/ml (1:200000) or, for dental anaesthesia, 12.5 micrograms/ml (1:80 000). Epinephrine is contraindicated for ring block of digits or the penis and for other procedures associated with risk of ischaemia. The maximum cumulative safe doses of lidocaine for adults and children are:
|0.5%, 1 % lidocaine||4 mg/kg|
|0.5%, 1 % lidocaine + epinephrine 5 μg/ml (1:200 000)||7 mg/kg.|
|Anaesthetic procedure||Concentration (%)||Epinephrine||Dose|
|Local infiltration and peripheral nerve block||0.5||No||50||250|
|Pharynx, larynx, trachea||4||No||1-5||40-200|
(+ 7.5% glucose)
The table provides a general guide to dosage in adults. Smaller dosages should be administered to debilitated, elderly, epileptic and acutely ill patients. Solutions containing preservatives should not be used for spinal, epidural, caudal and intravenous regional anaesthesia.
Spinal anaesthesia should only be attempted by a person trained in the technique and competent to treat possible complications. A “heavy” solution (5% lidocaine in 7.5% glucose) will provide the muscular relaxation required for abdominal surgery. Full aseptic technique must be employed for the injection and the pa dent must be appropriately tilted to ensure safety and the required level of analgesia.
Spinal anaesthesia always causes hypotension as a result of sympathetic blockade. It should never be used in patients with any condition resulting in hypovolaemia. The hypotensive response may largely be averted by preliminary intravenous infusion of 500-1000 ml of physiological saline (9 mg/ml) but blood pressure should always be measured every 2 minutes for at least 10 minutes. Postoperative headache can be prevented by instructing the patient to remain supine for 24 hours.
Lumbar epidural block has largely replaced caudal epidural block for relief of pain in labour. It requires less local anaesthetic, carries less risk of infection and is readily extended should caesarean section become necessary. However, because of the risk to both the mother and the fetus, it should be attempted only by an experienced specialist anaesthetist.
Maternal blood pressure, fetal heart rate and uterine contractions should be monitored throughout the procedure. Paracervical block is no longer recommended during labour because it results in very high levels of the drug in fetal blood.
Use in pregnancy
Safe use in early pregnancy has not been established. However, there is no clinical evidence to suggest that exposure of the mother to lidocaine is harmful to the fetus.
Co-administration of oxytocic drugs postpartum may cause severe and prolonged hypertension. The use of lidocaine preparations containing epinephrine during or following the administration of halothane or trichloroethylene creates a risk of cardiac dysrhythmias.