Impact of carpule solution components on the development of allergy
To understand the nature of allergic manifestations, it is necessary to examine in detail the composition of modern carpules. In addition to the main active substance that ensures the blockade of nerve impulses, they contain additional chemical compounds. These are often the cause of unexpected immune system reactions.
Key additives in dental solutions:
- Preservatives. Their main task is to maintain absolute sterility of the liquid inside the carpule.
- Antioxidants. The most famous representative of this group is sodium bisulfite. It is added to solutions containing vasoconstrictors (adrenaline or noradrenaline) to prevent their rapid oxidation. However, bisulfite is a potent allergen for specific groups of patients.
- Chelating agents (EDTA). These chemicals neutralize heavy metal ions (such as tin and aluminum) that can enter the liquid from the glass ampoule or packaging elements. If metal ions are not bound, they will cause rapid degradation of the vasoconstrictor component, sharply reducing the duration of anesthesia.
- Vasoconstrictors. Added to the composition to constrict blood vessels, which significantly enhances and prolongs the action of the main drug.
Mepivacaine as the drug of choice in patients with a burdened history
The drug Mepivacainum (known on the market as scandonest, carbocaine, mepidont, or scandicaine) occupies a special place in a doctor's practice. Its uniqueness lies in the possibility of use without the addition of a vasoconstrictor at all, which radically reduces the risk of complications in certain patient groups.
Who is mepivacaine indicated for in the first place:
- Patients suffering from bronchial asthma and allergies to any sulfur-containing medications. Since 3% mepivacaine solution contains no vasoconstrictor, the antioxidant sodium bisulfite—the main trigger of attacks in such individuals—is not added.
- People with acute intolerance to adrenaline (e.g., in severe cardiovascular pathology, pronounced thyrotoxicosis, or diabetes mellitus).
- In geriatric and pediatric dentistry, where the gentlest possible effect on the body is required.
It is important to note that true allergic reactions to mepivacaine itself are extremely rare. If they do occur, they manifest as urticaria or angioedema. At the same time, cross-allergy with other local anesthetic drugs is not observed, making it a reliable backup option.
Contraindications and systemic toxicity of mepivacaine
Despite its high safety profile, mepivacaine has strict limitations. It is strictly contraindicated in confirmed hypersensitivity, severe liver damage, porphyria (porphyria), and myasthenia gravis (myasthenia).
Allergy should not be confused with systemic toxic effect, which occurs not due to an immune response, but as a result of accidental intravascular administration of the drug. Toxicity manifests completely differently:
- Central nervous system: the patient may fall into a state of depression or, conversely, euphoria. Impairments of the swallowing reflex, vision, and speech are observed. In severe cases, seizures and respiratory depression develop, up to coma.
- Cardiovascular system: sharp drop in blood pressure (hypotension) and bradycardia.
To prevent toxic effects, dosage is strictly observed: the maximum injection dose is 4.4 mg per kilogram of body weight, but absolutely no more than 300 mg per single administration.
Alternatives: topical anesthesia with bumecaine
In cases where it is only necessary to anesthetize the oral mucosa or suppress an pronounced gag reflex, injections can be avoided entirely. For this purpose, bumecaine (pyromecaine) is used.
In dental practice, it is used exclusively in the form of applications (topically). For example, a 1% solution is applied to suppress the gag reflex before taking impressions. For stomatitis, gingivitis, or to anesthetize the needle insertion point, a 1–2% solution or 5% pyromecaine ointment is used.
An interesting option is a combined ointment containing 5% pyromecaine and 5% methyluracil. Methyluracil in this composition acts as a regeneration stimulant and a potent anti-inflammatory agent. This combination is prescribed from one to three times a day, but the total dose of the ointment must not exceed 1 gram under any circumstances to avoid adverse events.
Briefly: answers to topical questions
Which local anesthetics belong to the chemical group of amides?
The chemical group of amides includes the following drugs:
- Articaine (Articainum) — the first amide anesthetic with a thiophene ring.
- Bumecaine — synonym pyromecaine.
- Bupivacaine — synonym marcaine.
- Lidocaine (Lidocainum) — a universal drug for all types of anesthesia.
- Mezocaine — synonym trimecaine.
- Mepivacaine (Mepivacainum) — synonym isocaine.
- Ropivacaine — a representative of the amide group.
Amides are metabolized by microsomal liver enzymes, are not degraded by plasma and tissue esterases, and therefore act longer than esters and less frequently cause allergic reactions.
What is the mechanism of action of local anesthetics on the nerve fiber membrane?
The mechanism of action of local anesthetics consists in reducing the permeability of cell membranes to sodium and potassium ions, which leads to the blockage of the action potential.
The penetration of drugs through the nerve fiber membrane occurs according to the law of simple diffusion. The effectiveness of action is directly proportional to the concentration of the anesthetic base on the outer membrane. The drugs block the conduction of the pain impulse at the initial stage, acting on sensitive nerve endings. After the action terminates, the function of the nerve fibers is fully restored.
Which nerves are blocked during mandibular anesthesia?
During mandibular anesthesia (at the mandibular foramen), the following nerves are blocked:
- Inferior alveolar nerve — its blockade is the main goal of the intervention.
- Lingual nerve — is blocked simultaneously with the performance of anesthesia at the mandibular foramen.
- Buccal nerve — can be blocked using the apodactyl method or additionally, since its blockade must always be combined with inferior alveolar nerve anesthesia when treating posterior teeth.
Also, simultaneous blockade of the lingual, buccal, and inferior alveolar nerves is achieved during Gow-Gates mandibular anesthesia.
Class and exam questions
Why are solutions with adrenaline contraindicated in patients with bronchial asthma?
Solutions with adrenaline contain a preservative-antioxidant — sodium bisulfite. It is capable of provoking a severe allergic reaction or an attack in asthmatics and individuals with sulfur-containing drug intolerance.
Can mepivacaine be used if the patient is allergic to other anesthetics?
Yes, mepivacaine is considered a safe choice, as cross-allergy with other local anesthetics is not observed. Allergy to the drug itself (urticaria, angioedema) is extremely rare.
How to distinguish an allergic reaction from the toxic effect of an anesthetic?
Allergy manifests as urticaria or angioedema. Toxic effects occur when the drug enters a vessel and are accompanied by systemic disorders: euphoria, seizures, speech disorders, bradycardia, and hypotension.
Why are heavy metal-binding substances added to local anesthetics?
Such components (e.g., EDTA) are necessary to neutralize aluminum and tin ions entering the solution from the packaging. If they are not bound, they will cause rapid degradation of the vasoconstrictor.
What else to study on this topic
- Technique of intraligamentary anesthesia with mepivacaine
- Conduction anesthesia in the upper and lower jaw
- Pharmacodynamics and metabolism of bumecaine
- First aid for intravascular administration of an anesthetic
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