Local Anæsthetic Allergy & Testing
Following the administration of a local anæsthetic, a minority of patients may suffer
one of a range of unwanted symptoms.

Some of these symptoms can be mistaken for
hypersensitivity or allergy & the
patient unnecessarily told they are allergic to the anæsthetic.  Mislabelling of
patients as allergic to
local anæsthetic can lead to problems for dentists with
patients unable to undergo routine dental treatment.

Local anæsthetics can be categorised into 2 classes:

amides (lidocaine, bupivacaine, prilocaine, ropivacaine, articaine,
mepivacaine) &

esters (benzocaine, cocaine, procaine, tetracaine).

True allergy to an amide local anæsthetic is exceedingly rare.

Local anæsthetics of the ester type are more likely to produce allergic reactions
as they are metabolised to
para-aminobenzoic acid (PABA) which is an allergenic
compound.  The only
ester local anæsthetic used in dentistry is benzocaine, which
is used in topical preparations applied prior to administration of
local anæsthetic

An allergy to one
ester local anæsthetic contra-indicates the use of another ester,
as the metabolism of all
esters yields PABA.

Patients are unlikely to show cross sensitivity to
amide local anæsthetics as these
are not metabolised to

Allergy to one
amide local anæsthetic does not contra-indicate use of another
amide local anaesthetic.  However, it would be unwise to use another amide local
without hypersensitivity tests.

Local anæsthetics are considered relatively safe but, given the high number of
injections that are administered, adverse reactions are inevitable.

Adverse systemic reactions to local anæsthetics can be divided into 3 categories:

1.        Allergy
2.        Psychogenic &
3.        Toxic.

Signs & Symptoms of Local Anæsthetic Hypersensitivity

A true allergy to local anæsthetics may be either type I or type IV.

Type I; immediate anaphylactic reactions mediated by IgE antibodies.  Signs and
symptoms of
Type I Allergy tend to occur within minutes of giving the injection:

  • The lips & peri-orbital areas swell (angio-œdema)
  • The patient may become agitated & there is generalised urticaria (‘hives’) &
    pruritus (itchiness), particularly of the hands & feet.  Other symptoms include
    abdominal cramps, nausea & diarrhœa
  • Tightness of the chest, with wheezing & dyspnœa (difficulty in breathing) may
  • There may be a fall in blood pressure & a rapid thready pulse, which may be
    accompanied by flushing of the skin or rash.

Type IV; delayed hypersensitivity reactions mediated by sensitised lymphocytes
(‘white blood cells’):

  • Usually localised to the injection site
  • Commonly expressed as a contact dermatitis

Alternative diagnoses

Genuine hypersensitivity reactions to local anæsthetics are extremely rare.

It has been estimated that true allergic reactions to
local anæsthetics account for
< 1% of all adverse reactions to
local anæsthetics.  It is unclear where this figure
originates from or the number of patients this represents, as the incidence of
adverse reactions occurring in patients who have received
local anæsthetics is not

Adverse reactions commonly mistaken for hyper-sensitivity reactions include
syncope (fainting), panic attacks & toxic effects due to inadvertent entry of the
drug into the circulation.

The following are possible differential diagnoses and their symptoms:


Many allergic reactions involving local anæsthetic preparations are due to other
constituents in the injection solution rather than to the drug itself such as
preservatives (e.g.
benzoates – used in multi-dose vials) & anti-oxidants (e.g. meta-
, used in local anæsthetic solution containing adrenaline) can cause
allergic reactions.

Allergy to
latex contained in rubber bungs, natural rubber latex gloves, rubber
dams & other dental materials should also be considered.

Historically, the most sensitising components in
local anæsthetic solutions were
preservatives such as
methylparabens.  Parabens are no longer added to dental
local anæsthetic solutions available in the UK.


Psychogenic reactions (originating in the mind, an emotional response) are one of
the most common adverse reactions associated with
local anæsthetic use in

They may manifest in many ways, the most common being
syncope but other
symptoms include panic attack,
hyper-ventilation (rapid breathing), nausea (feeling
sick), vomiting & alterations in heart rate or blood pressure, which may cause
pallor (paleness).

They can be misdiagnosed as allergic reactions & may also mimic them with signs
such as flushing of the skin, blotchy red rash,
œdema (swelling) & broncho-spasm
(shortness of breath).  All patients have some degree of autonomic response to
injections, ranging from slight
tachycardia (increased heart rate) & sweating to
syncope (fainting).


Toxic reactions may occur if high levels of anæsthetic enter the blood stream.  
Local anæsthetics can reach the systemic circulation as a result of repeated
injections, inadvertent
intra-vascular administration or overdose in those patients
who have problems eliminating or metabolising the
local anæsthetic.

Toxic side effects are predominantly
neurological & include excitability / agitation,
sedation, light-headedness, slurred speech, mood alteration,
diplopia (double
vision), disorientation & muscle twitching.  Higher blood levels may result in
tremors, respiratory depression & seizures.

Vaso-constrictor agents such as adrenaline may also cause adverse effects.  
Adrenaline toxicity can result in symptoms such as anxiety, restlessness,
trembling, pounding headache, palpitations, sweating, pallor, weakness, dizziness
& respiratory distress.

Toxic reactions can be minimised by staying within safe dosage parameters &
using safe injection techniques.

Management Options To Prevent Adverse Effects Occurring

When a patient experiences signs & symptoms that are suggestive of an allergic
reaction, possible alternative causes should be considered such as contact with
other common allergens, toxic dose or a psychogenic reaction.

The possible causes of the symptoms experienced should be discussed with the

Use of the terms ‘
allergic’ & ‘allergy’ should be avoided when discussing any
adverse event as these terms are recognised by patients & readily adopted as the

Adverse reactions caused by toxicity or anxiety can be minimised by:

  • Administering injections with an aspirating syringe to avoid intra-vascular

  • Relaxing nervous patients to relieve their anxiety.  For extremely anxious
    patients, sedation may be required.

  • Treating patients in a supine position to prevent fainting.

  • Giving injections slowly to reduce discomfort & improve localisation of solution.

  • Restricting the total dose given to the patient to prevent toxic effects occurring
    by overdose.  The maximum dose for the individual patient can be calculated
    using the dosage information contained in the package insert or recognised
    dental textbooks on local anæsthetic, & taking into account the age & weight
    of the patient, any concomitant drug therapy & underlying medical conditions.

Management of a Patient Who Suffers an Adverse Reaction in the Surgery

Psychogenic reaction:

  • If a fall in blood pressure occurs or the patient feels faint, laying the patient flat
    & elevating the legs should be sufficient to help restore the blood pressure.

  • Any tight clothing around the neck should be loosened.

  • Once conscious, the patient should be given a glucose drink.

  • Calm the patient and reassure them.

Toxic reaction:

Symptoms caused by toxicity will be short-lived in most patients.  The pharmaco-
kinetics of the
local anæsthetics used in dentistry suggest that the drug will be
eliminated from the blood stream within a couple of hours, but may be as long as
12 hours in some individuals.

Reassure the patient that they will feel better after several hours & inform them
that although the reaction is unpleasant, it should not happen again & it is not
necessary to avoid that
local anæsthetic in the future.

Management of a Patient When Local Anæsthetic Allergy Is Strongly

If symptoms suggestive of a true allergic reaction occur (localised reaction
consisting of swelling, erythema, an itchy rash or systemic features such as
dyspnoea, wheezing, widespread skin rash or circulatory collapse), the patient
should be given emergency treatment following the ‘
Emergency treatment of
anaphylaxis guidelines’.

If the patient feels unwell, their condition is deteriorating or they are very
distressed, they should be transferred to hospital.

The patient should be referred for further investigation to confirm if the
or another possible allergen (e.g. preservative or latex) was the cause
of the adverse effects.

If the cause of the symptoms is uncertain, dentists should contact the local (dental)
hospital to discuss referring the patient for further investigation.  Alternatively, if a
true allergic reaction is suspected, patients can be referred by the dentist or GP
directly to the 'allergy clinic' at their local hospital, if this service is available.

Location and contact details for allergy clinics can be found via the
British Society
for Allergy and Clinical Immunology website.  Alternatively, several dental hospitals
run this service (such as Guy's Dental School).

Very rarely, allergy to the
local anæsthetic is confirmed.  In these cases,
immunological testing should be extended to other
local anæsthetics in order to
identify a safe alternative for future dental procedures.

Management of Patients who Report to be Allergic to Local Anaesthetic

New patients who claim to have had an allergic reaction to a local anæsthetic
should be carefully questioned to obtain a history of past events.  These details
may be more reliably obtained from the patient’s previous dentist.

Questions to ask the patient or previous dentist include:

  • What symptoms did the patient experience?
  • What explanation for the symptoms was given at the time? Who told them this?
  • Have they ever had any other dental treatment or surgery in the past that
    required them to have a local anaesthetic agent – what happened?
  • Have they any other allergies?
  • Have they ever been tested for a local anaesthetic allergy? If so, what was
    the result? (The allergy specialist should be contacted for confirmation and
    further information).


  • If further information obtained strongly suggests an allergy but no details are
    available, refer the patient for allergy testing.
  • If further information strongly suggests a psychogenic reaction, proceed with
    care & address the patient’s anxiety.
  • If further information strongly suggests toxicity, proceed with care starting with
    low doses of local anæsthetic / vaso-constrictor.
  • If no information is available from the patient or dentist, contact the GP who
    may have information about previous local anæsthetic exposure or other
    relevant knowledge.
  • If it is strongly suspected that the patient has previously suffered an allergic
    reaction to a local anæsthetic & emergency dental treatment is required,
    consider contacting a local hospital Dental / Oral Surgery department to
    discuss management & referral to a unit that has full resuscitation facilities
Last Updated 7th June 2013
Useful Websites:

British Society for Allergy and Clinical Immunology

Oral Medicine Department, Guy's Dental Hospital

Useful Articles:

Anesth Prog 1987.  A Guideline to Local Anesthetic Allergy Testing

Anesth Prog 1997.  The Incidence of Complications Associated with Local
Anesthesia in Dentistry

BDJ 1999.  Case Study.  Allergic Reactions to Lignocaine

BDJ 2000.  Case Study.  Adverse Reaction to Dental Local Anaesthetic Injection –
‘Allergy’ is not the cause

Allergol & Immunopathol 2002.  Allergy to Local Anaestheics in Dentistry.  Myth or

Dent Clin N Am 2002.  Adverse Drug Reactions to Local Anesthesia

Can J Anaesth 2003.  Editorials.  Allergies to Local Anaesthetics – The Real Truth

CDAJ 2006.  Local Anesthetics – Dentistry’s Most Important Drugs, Clinical Update

Am J Med Sci 2007.  Approach to Patients with Suspected Hypersensitivity to
Local Anesthetics

Clinical & Experimental Allergy 2008.  BSACI Guideleines.  BSACI Guidelines for
the Management of Drug Allergy

Current Allergy & Clinical Immunology 2009.  Hypersensitivity to Local Anaesthetics
– 6 Facts & 7 Myths

Dental Update 2011.  Allergy to Local Anaesthetic Agents used in Dentistry – What
are the Signs, Symptoms, Alternative Diagnoses & Management Options