Why reactions to LA are important

Local anaesthetics (LA) are widely used in healthcare procedures including dental, surgical, emergency, obstetric, ophthalmic and dermatological. Most people will be exposed to LA at some time in their life.

Reactions to dental LA injections (with or without vasoconstrictor) are mostly psychogenic. Inadvertent intravascular administration or excessive dose can lead to toxic effects from the LA or vasoconstrictor. Allergy to LA  preparations used in dentistry is very rare.

If a reaction occurs, document it accurately in the patient record. If a person is mistakenly labelled as allergic to LA, their future management may be compromised. When treating patients with a history of reaction to dental LA, explore the nature of the reaction to inform future management.

Psychogenic reaction

Psychogenic reactions (due to psychological or emotional factors) are the most common adverse reactions associated with LA use in dentistry. They are more likely if patients are afraid of visiting the dentist, and may also be associated with anxiety or panic attack. A ‘fight or flight’ response from the sympathetic nervous system leads to release of adrenaline and cortisol.

Signs and symptoms

Symptoms range from light-headedness and sweating to fainting (vasovagal syncope).

Syncope is a transient loss of both consciousness and postural tone. Vasovagal syncope usually occurs due to emotional stress. It occurs rapidly and patients recover quickly (within two minutes) and spontaneously. Patients may experience ‘pre-syncope’ symptoms of facial pallor, sweating, nausea and warmth, even if they don’t faint.

Anxiety symptoms include faster, irregular or more noticeable heartbeat, light-headedness, dizziness, headache, chest pain, loss of appetite, sweating, breathlessness, feeling hot and shaking.

Under stressful circumstances, some patients hyperventilate. This gives rise to feelings of faintness but does not usually result in syncope. Hyperventilation, tachycardia and anxiety-related rash are also symptoms of panic attack.

Acute management

To manage a dental patient who has fainted:

• lay the patient flat
• raise legs to restore cerebral blood flow
• loosen tight clothing around the neck
• when conscious, give fruit juice or a sugar-containing drink

Reducing risk of reaction

To help prevent a psychogenic reaction:

• reassure patients who have had a previous psychogenic reaction
• reassure nervous or anxious patients
• treat patients in a reclined position to prevent fainting
• agree a ‘stop-signal’ with the patient so they feel in control
• remind patients not to skip breakfast before dental appointments
• for extremely anxious patients, consider sedation

Toxic effects and adverse reactions

Toxic effects occur if dental cartridge contents are inadvertently administered intravascularly or an excessive dose is used. Toxic effects are unlikely if the injection is administered correctly and at the correct dose for the patient.

Some patients are sensitive to the effects of adrenaline, used as a vasoconstrictor. They may experience ‘adrenaline rush’, similar to the psychogenic ‘fight or flight’ response, despite correct dose and administration.

Signs and symptoms

Signs and symptoms of toxicity are predictable and dose-related. Rate of onset and severity of symptoms relate to the level of medication in the blood stream.

Symptom onset after intravascular administration is immediate; onset after correct administration of a toxic dose is 5 to 10 minutes, longer in people with liver impairment.

LA component

Signs and symptoms of toxicity include dizziness, metallic taste, auditory and visual disturbance, apprehension, disorientation and circumoral anaesthesia. At higher blood levels, patients may experience drowsiness, slurred speech and convulsions.

Vasoconstrictor component

Adrenaline causes palpitations, tachycardia, light-headedness, sweating and headache. Felypressin, included in some dental LA preparations, can cause headache, vertigo, sweating and tremor but does not have cardiac effects.

Patients sensitive to adrenaline may experience symptoms such as restlessness, sweating, dizziness and warmth, even if the dose and route are correct. These symptoms mimic those of endogenous adrenaline release and are enhanced in anxious patients.

Acute management

Severe toxicity is unlikely at doses used in dentistry. If severe effects occur, monitor vital signs and administer oxygen. Reassure the patient that effects will be transient and self-limiting.

Symptoms will generally be short-lived and subside as the LA and vasoconstrictor are excreted. After intravascular administration, symptoms last only a few minutes; following excessive dose they typically last 5 to 10 minutes, longer in people with liver impairment.

Reducing risk of reaction

Ensure dose is appropriate for the patient’s age and weight. Follow product information for dose reduction in people with liver impairment. See drug interactions with dental local anaesthetics for situations when dose adjustment due to other medicines should be considered.

Intravascular administration can be avoided by careful injection technique and use of an aspirating syringe. Give injections slowly (no more than 1ml per minute) to improve localisation of the solution.

For people sensitive to adrenaline, consider using a preparation:

• with a lower concentration of adrenaline (1:200,000 rather than 1:80,000)
• with felypressin instead of adrenaline
• without a vasoconstrictor

Allergy

Allergy to amide LA is exceedingly rare. Allergic reactions to felypressin or metabisulfites have been reported but are also rare. It is not possible to be allergic to adrenaline.

In the past, some dental preparations contained ester LA, methylparabens preservatives and latex, all known to cause allergic reactions; these substances are no longer used in UK dental LA injections.

Allergic reactions may be immediate (type 1) or delayed (type IV). Immediate anaphylactic reactions, mediated by IgE antibodies, can be life-threatening. Delayed reactions, mediated by sensitised lymphocytes, are usually localised to the injection site.

Signs and symptoms

Immediate hypersensitivity reactions present with symptoms of angioedema (swelling of the face, tongue, lips, throat, larynx or periorbital area) or sudden-onset wheezing, difficulty breathing or noisy breathing. Patients may also suddenly feel faint, dizzy, tired or confused and there may be generalised urticaria and pruritis.

Delayed hypersensitivity reactions are more likely than immediate reaction but are still very uncommon. They present as localised erythema, oedema and itching, hours to days after the injection and usually peak within 72 hours. Delayed hypersensitivity reactions do not progress to anaphylaxis and are not dangerous.

Acute management

Anaphylaxis is a medical emergency. Immediately call for an ambulance and begin initial anaphylaxis treatment, place the patient in a comfortable position and administer intramuscular adrenaline.

Delayed hypersensitivity reactions generally occur after the patient has left the dental setting. Patients may present to a pharmacist or GP or self-treat with oral antihistamines. Topical steroids may be required.

Reducing risk of reaction

Patients who have experienced immediate or delayed hypersensitivity reactions can be referred for allergy testing. Liaise with the patient’s GP who can make the referral. In the rare circumstance that allergy to LA, felypressin or metabisulfite is confirmed, that substance should be avoided thereafter.

Contents of dental LA cartridges

Reactions to a dental LA injection can be due to any of its constituents (or none, in the case of psychogenic reaction). Dental cartridges used in primary care dentistry contain a LA, usually with a vasoconstrictor (adrenaline or felypressin); they are administered using a dental cartridge syringe and needle.

Local anaesthetic

LAs are categorised as amide (lidocaine, prilocaine, articaine, mepivacaine) or ester (benzocaine, procaine, tetracaine). All dental LA injections currently used in the UK are amide.

Vasoconstrictor

Dental LA usually contain a vasoconstrictor to reduce local blood flow, slow the rate of absorption and prolong the anaesthetic effect.

Adrenaline is most commonly used. Felypressin, a synthetic analogue of vasopressin, is useful when adrenaline should be avoided.

Excipients

Adrenaline-containing dental cartridges contain sodium metabisulfite or potassium metabisulfite as an antioxidant. Some also contain disodium edetate as a chelating agent. Metabisulfites and disodium edetate are widely used as preservatives in pharmaceuticals and food products.

All dental cartridges contain sodium hydroxide and/or hydrochloric acid for pH adjustment plus sodium chloride and water as diluents.

The following preparations are available as dental cartridges in the UK. Common brand names are listed as examples:

• Lidocaine 2% with adrenaline 1:80,000 (Lignospan Special, Xylocaine)
• Articaine 4% with adrenaline 1:100,000 or 1:200,000 (Septanest, Anestadent, Orabloc)
• Prilocaine 3% with felypressin (Citanest with Octapressin)
• Mepivacaine 2% with adrenaline 1:100,000 (Scandonest 2% Special)
• Mepivacaine 3% (no vasoconstrictor) (Scandonest Plain)

Further details can be found in product Summaries of Product Characteristics

References

Available on request

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