Chemical nature and pharmacological advantages
From a chemical standpoint, lidocaine is a substituted amide derived from acetanilide. The drug is readily soluble in both water and alcohol.
Belonging to the amide group determines its metabolic features: it is broken down in the body significantly slower than local anesthetics with an ester structure (e.g., procaine). This provides a longer duration of action.
Compared to classical ester anesthetic agents, lidocaine has a number of distinct advantages:
- High potency: its local anesthetic effect is approximately 2.5 times superior to that of procaine.
- Speed: the anesthetic effect develops much faster.
- Duration: the duration of anesthesia is doubled.
- Hypoallergenicity: lidocaine is the drug of choice for patients with diagnosed intolerance to procaine and other esters.
Indications for use
The drug is considered a universal anesthetic because it is effective for all types of local anesthesia. The specific route of administration (local or parenteral), as well as the volume and concentration of the solution, are always selected individually based on the nature of the surgical intervention.
Main areas of use:
- Infiltration anesthesia: widely used in various surgical operations for layer-by-layer tissue infiltration.
- Nerve block anesthesia: in demand in dental practice, limb surgery, and for performing major nerve plexus blocks.
- Epidural and spinal anesthesia: used for surgical interventions on the pelvic organs and lower extremities.
- Surface (topical) anesthesia: used for anesthesia of mucous membranes in urology, ophthalmology, dentistry, during bronchoscopy, and to relieve symptoms in burns.
Side effects and signs of intoxication
The toxicity of lidocaine directly correlates with the concentration used. When using weak solutions (0.5%), the safety profile is comparable to procaine. However, when the concentration is increased to 1–2%, the risk of adverse reactions increases significantly.
In case of overdose or systemic intoxication, the following symptoms develop:
- Central nervous system: patients may complain of headache, dizziness, tinnitus, and visual disturbances. Numbness of the tongue and oral mucosa frequently occurs. Drowsiness or, conversely, marked agitation is possible.
- Motor sphere: extremity tremor and convulsive muscle twitching are observed.
- Cardiovascular system: development of bradycardia (decreased heart rate) is characteristic.
- Severe cases: with severe intoxication, there is a risk of dangerous respiratory depression.
Drug interactions
Lidocaine is frequently used in combinations, which allows modifying its effects and safety profile.
- With vasoconstrictors: To prolong the anesthetic effect, epinephrine (as a 0.1% solution) is added to the lidocaine solution. This causes vasoconstriction at the injection site, which slows down the absorption of the anesthetic into the systemic circulation and reduces the risk of resorptive toxic reactions.
- With sulfonamides: Unlike procaine, the metabolism of lidocaine is not accompanied by the formation of para-aminobenzoic acid (PABA). Due to this, lidocaine does not reduce the antimicrobial activity of sulfonamide drugs at all, making their combined use completely safe.
Briefly: answers to topical questions
What is the mechanism of the local anesthetic action of lidocaine?
The mechanism of the local anesthetic action of lidocaine consists in the blockade of sodium channels. The drug prevents the influx of sodium ions, which disrupts the depolarization of the cell membrane. Lidocaine belongs to local anesthetics for which sodium channel blockade is the primary mechanism of action.
In what types of cardiac arrhythmias is lidocaine indicated?
Lidocaine is indicated for the treatment of various ventricular arrhythmias. The drug is used in the following conditions:
- Ventricular tachycardia and extrasystoles.
- Ventricular arrhythmias in the acute period of myocardial infarction (is the drug of choice).
- Ventricular tachycardias due to cardiac glycoside intoxication.
- Ventricular tachycardias after cardiac surgery.
- Polymorphic ventricular tachycardia (Torsades de pointes) as part of combination therapy.
What are the contraindications for the use of lidocaine?
Contraindications to the use of lidocaine are severe cardiac conduction disorders and individual intolerance. The drug must not be used in the following conditions:
- Hypersensitivity to lidocaine itself, as well as to other components of the drug (e.g., epinephrine or sulfates).
- Sick sinus syndrome (especially in elderly patients).
- Atrioventricular block.
- Pronounced bradycardia.
- Cardiogenic shock.
Where and with the participation of which enzymes does the metabolism of lidocaine occur?
The metabolism of lidocaine occurs predominantly in the liver with the participation of microsomal enzymes. The drug belongs to the amide group, therefore its biotransformation is carried out by the hydrolysis of microsomal liver enzymes. Lidocaine is characterized by high presystemic metabolism (first-pass effect through the liver), due to which it is almost completely inactivated during passage through the portal circulation.
What is the maximum allowable dose of lidocaine for infiltration anesthesia?
The maximum permissible dose of lidocaine for injection, including infiltration anesthesia, is 4.4 mg/kg of body weight, but not more than 300 mg.
Lidocaine is a dual-purpose drug: it "freezes" nerve impulses (local anesthetic) and "calms" the heart rhythm (antiarrhythmic).
Class and exam questions
Why is lidocaine often combined with an epinephrine solution?
Epinephrine has a vasoconstrictor effect. Its addition slows down the absorption of lidocaine into the blood, which prolongs the duration of anesthesia and reduces the risk of systemic intoxication.
Can lidocaine be prescribed to patients taking sulfonamides?
Yes, it is possible. The metabolism of lidocaine does not release para-aminobenzoic acid (PABA), so it does not hinder the antibacterial action of sulfonamides.
How does lidocaine toxicity depend on solution parameters?
Toxicity directly depends on the concentration. A 0.5% solution is comparable in safety to procaine, whereas 1–2% solutions have significantly higher toxicity.
What should be done if a patient is allergic to procaine?
In case of procaine intolerance, lidocaine becomes the drug of choice, since it belongs to a different chemical group (amides rather than esters).
What else to study on this topic
- Detailed mechanism of the antiarrhythmic action of lidocaine
- Comparative analysis of the metabolism of amides and esters
- Criteria for selecting the concentration and volume of the solution for various types of anesthesia
- Pathogenesis of seizures and respiratory depression in overdose
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