Understanding Your Reaction to Local Anesthetics

Have you ever had a cavity filled? Do you have a dental crown? If so, chances are you have been exposed to local anesthetics. In almost all dental procedures, along with other minor surgeries, local anesthetics are crucial to manage pain during the operation. Considering this, various challenges may arise if a patient is allergic to these drugs. While many people have reactions following exposure to local anesthetics, it is important to identify whether those reactions are truly allergic.

What are local anesthetics?

Local anesthetics block pain signals from being sent from your nerves to your brain. This allows for medical and dental procedures to be properly performed while avoiding the pain it would otherwise cause. These drugs can be classified as either esters or amides, depending on their structure. Ester compounds typically have a slower onset than amide compounds. Hence, dentists typically prefer to use anesthetics of the amide class. Due to its high efficacy, Lidocaine, an amide compound, is most often used. Many local anesthetics, including Lidocaine, also contain epinephrine, which is meant to extend the length of time that the anesthetic is effective and reduce bleeding. Some may also contain metabisulfite to prevent epinephrine degradation or methylparaben to prevent bacterial growth.

Is my reaction truly allergic?

Some people may experience an adrenaline rush after injection with a local anesthetic, including anxiety, heart palpitations, sweating, flushing, shortness of breath, or nausea. Oftentimes, they mistake this as an allergy to the anesthetic. However, this is a normal sympathetic response to the epinephrine that was present in the solution.

During a true allergic reaction, antibodies specifically target and bind to the allergen. This causes other cells, such as mast cells or basophils, to release histamine. Histamine causes symptoms such as itching, rash, hives, or swelling. For this reason, allergic reactions are typically characterized by the immediate onset of these symptoms following allergen exposure. Severe reactions may also result in anaphylaxis. Of all the people who report reactions to local anesthetics, only 1% have true allergies to them.

It is important to note that the metabisulfite and methylparaben found in many anesthetics are also common allergens. Additionally, anesthetics of the ester class may break down into para-aminobenzoic acid, another common allergen. Exposure to these may result in an allergic reaction as described above, although this indicates an allergy to those specific compounds, not to the anesthetic itself.

Anesthetic allergy testing

To determine whether or not you have an allergy to local anesthetics, skin testing may be performed. In this procedure, the allergen is introduced into the skin and the skin is monitored for itchiness, redness, or the formation of a bump, all signs of an allergic reaction. Skin testing first involves exposure to the skin surface via prick testing, followed by intradermal testing if results are negative. If both prick and intradermal results are negative, you may undergo a graded challenge to further evaluate possible allergies. This involves the subcutaneous injection of increasing doses of the allergen, with an observation period following each dose. The local anesthetics used for these procedures should be free of any additives, such as epinephrine, parabens, or sulfites. This is important to identify if the reaction is due to the additives, or the anesthetic itself. Additionally, it may be useful to test drugs from both the amide and ester classes. This way, even if you react to one class, it will confirm that it is safe to use the other class for procedures requiring pain relief.

What do my skin testing results mean?

Understanding skin testing results is essential for dentists and doctors to administer pain management drugs that are safe for you. A reaction to only ester anesthetics may permit the use of amides instead, and vice versa. A reaction to only amide anesthetics may also permit the use of other amides because these compounds have a low risk of cross reactivity. 

You may find that while you had an allergic reaction after anesthetic exposure, skin testing results were negative. In this case, the reaction may have been due to the additives commonly found in solutions, which were absent during skin testing. Anesthetics free of epinephrine, parabens, and sulfites may still be used in this scenario, and should not trigger an allergic reaction. This is an important distinction to make so that you are not mistakenly labeled with an allergy to local anesthetics, as this would place unnecessary limitations on your access to pain management drugs during dental and medical procedures.