Allergic Reactions to Local Anesthesia is quite rare but when it does happen, it can turn complicated very fast and requires immediate response from the Dentist and Dental Staff to make sure that the vitals of the patient are kept Stable. Local Anesthesia is categorized into 2 types – Amides (Lidocaine, bupivacaine, prilocaine, articaine etc) and Esters (benzocaine, cocain, procaine, tetracaine). Most common culprits showing allergic reaction are Esters (Benzocaine is commonly used in Dentistry) as they are metabolized into para-aminobenzoic acid or PABA which is a known allergenic compound.

There are four types of reactions seen due to Local Anesthesia

1.Allergic reaction: Avil Injection followed by Hydrocortisone

Type I allergy to Local Anesthesia: It is the Acute type, which results in immediate anaphyactic reaction due to IgE antibodies and the reaction is seen within minutes of administering the injection. The Symptoms seen in Type I LA Allergy are

  • Swelling or Odema of the Lips and skin around the Eyes
  • Itching (pruritus) or Hives (utricaria) is commonly seen on the extremities (hands and feet).
  • Nausea, stomach pain and diarrhea is also seen
  • Cold extremities, low Blood Pressure, increase in pulse rate

Type IV allergy to Local Anesthesia: It is the delayed type where hypersensitivity is seen due to the sensitized lymphocytes or WBC. The symptoms of Type IV Local anesthesia Allergy are

  • Redness and swelling at the injection site which is common to contact dermatitis
  • Ulceration at the site of injection

2.Syncope: Keep the patient awake and make him or her to take heavy breaths and it is best to make them smell Spirit on a Cotton (The pungent odor helps in improving the breathing).

These mostly come under Psychogenic reactions to LA which are mainly due to emotional response of the patient and it is in the head. Syncope is associated with hyper-ventilation, nausea, vomiting and increase or decrease in heart rate and Blood pressure leading to pallor of skin. Best treatment for such patients is to

3.Anaphylaxis: Adrenaline (Epinephrine) Injection – I.m, Oxygen Mask with 40% concentration and constant monitoring of the vitals (Oxygen saturation and Pulse) and transfer to the Emergency ward.

The component in Local Anesthesia which causes the Allergic or Anaphylatic reaction is the Preservative – Methyl Paraben. Even the local aesthetic agent is seen to cause allergic reactions but it is very rare. So there are special Local Anesthetic agents which do not contain Methyl paraben thus preventing the allergic reaction to the agent.

4.Toxicity: Toxicity due to LA is seen when the patient is given more than the required dose – Local Anesthesia Dosage

The Symptoms of LA toxicity is irregular heart rate, fluctuations in Blood Pressure and patient feels uneasy. Most Symptoms are neurological which induce agitation or excutability, light headedness, difficult in speaking, double vision, muscle twitching. In severe cases where the LA agent has entered the blood stream it can lead to tremors, seizures or respiratory depression. Vaso-constrictors such as Adrenaline should be administered to the patient to localize the LA and to reduce the spread of the solution in the blood stream. Giving Assurance to the patient is important to help them in relieving their Anxiety and psychological symptoms.

There are other complications due to faulty technique while administering Local Anesthesia such as Transient Hemifacial paralysis.

Local Anesthetic agents without Methylparaben (Preservative): Trade names

  • SEPTANEST1:100000 by Septodent which contains 4% atricaine with 1:100,000 epinephrine inj solution
  • ECOCAIN Inj 2%:

Procedure of Local Anesthesia Skin Test before Dental Surgery:

It is important to undergo this skin test in patients who have never undergone any Dental procedure in the past and has had no exposure to Local Anesthesia in their lifetime. I even recommend to conduct this test in patients who have undergone a procedure more that 10 years ago as there are chances that they might have acquired allergy to the solution in the mean time.

Source: J. P. Rood – “Adverse reaction to dental local anaesthetic injection – allergy is not the cause” – Case Study

Step 1: Prepare the first solution – 0.1ml of L.A + 0.9ml of Distilled water and load it in first syringe

Step 2: Prepare the second solution – 0.1ml of LA + 1.8ml of Distilled Water (double the first solution) and load it in second syringe

Step 3: Prepare the third solution – 0.1ml of LA + 2.7ml of Distilled Water and load it in third syringe

Step 4: Take the third solution and inject it in the forearm skin (Subcutaneous) of the patient  with the needle bevel facing towards the skin or outwards, once a bleb is seen press with your finger on it and hold for 5-10 mins. Check later to see if any inflammation or redness is seen in the injection site.

Step 5: If the tests are negative and there is no reaction or inflammation the above mentioned procedure should be performed using the other two syringes by having a spacing of 4 inches between each injection site.


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