What are Local Anesthetics?Local anesthetics, first developed in 1904, are commonly used to prevent pain in dental and surgical procedures. They are also used in injection form to treat and prevent irregular heart beats, in topical form to numb the skin (such as various anti-itch creams, like Lanacane) and mouth (such as Orajel), and in eye drops for surgical eye procedures.
Examples of local anesthetics include procaine (Novocaine), lidocaine (Xylocaine), benzocaine, and mepivacaine (Carbocaine).
What Symptoms Can Occur with Local Anesthetic Reactions?Many symptoms, due to allergic and non-allergic causes, can occur as a result of local anesthetic use. These symptoms may include:
- Fast heart rate or palpitations
- Swelling, itching, or hives, both at the site of injection and elsewhere on the body
- Signs of anaphylaxis
- Contact dermatitis at the site of injection or application
What Causes Reactions to Local Anesthetics?Reactions to local anesthetics are relatively common, although they are only rarely due to an allergic cause. Symptoms occurring after the use of local anesthetics may be due to a variety of causes, including anxiety, hyperventilation, toxic effects of the drug itself, vaso-vagal reactions, as well as reactions to epinephrine, which is frequently added to local anesthetics to make the numbing effect last longer.
It is also possible for a person to experience an allergic reaction to preservatives added to local anesthetics. Methylparabens are the most common preservatives added to multi-use vials of local anesthetics. Allergy to methylparabens, while still uncommon, is far more common than true allergy to local anesthetics themselves.
While true allergies to local anesthetics can occur, they are extremely rare despite numerous large studies of people who experienced adverse reactions after using these medications. Skin testing revealed that nearly all of these people showed no evidence of allergy to local anesthetics and were able to tolerate injections with these medications.
The possibility of latex allergy should always be considered when a person has a reaction to local anesthetics, given the common use of latex gloves in the medical and dental industries. Some medications used in spinal anesthesia contain sulfites, another preservative that can cause allergic reactions.
Lastly, it is possible to experience contact dermatitis to local anesthetics. An itchy, blistering rash may occur at the site of injection or application of the local anesthetic.
How is Allergy to Local Anesthetics Diagnosed?Skin testing can be helpful in the evaluation of an adverse reaction to these medications. Allergists have different ways of approaching a person with a history of an adverse reaction to local anesthetics. Most will, however, perform skin testing with the ultimate goal of giving a person at least one local anesthetic that can be used in the future.
Most allergists skin test with preservative-free (methylparaben-free), epinephrine-free local anesthetics. If skin testing is negative, then subcutaneous (under the skin) injections will be performed by the allergist using that specific local anesthetic. This is termed a “challenge”, which is essentially giving a person a typical amount of the drug that they might encounter at the dentist or when getting minor surgery. If a person tolerates a medically-supervised challenge using a particular local anesthetic, it is assumed that the person can use this particular drug in the future.
Other allergists will skin test using the most common local anesthetic available--lidocaine with methylparabens. The majority of people will tolerate a challenge using this form of local anesthetic, and therefore is the easiest way for a person to overcome the label of being “allergic to local anesthetics."
In the unusual circumstance that a skin test is positive to a local anesthetic, a repeat skin test using a methylparaben-free formulation or another local anesthetic can be performed. Common alternative local anesthetics for lidocaine include bupivacaine (marcaine), mepivacaine, prilocaine, and etidocaine. It is very important to always use local anesthetics that do not contain epinephrine for skin testing, since the presence of epinephrine could lead to a false negative skin test result.
Some people will notice a reaction at the site of injection hours to days after testing or challenge with a local anesthetic. This may signal the presence of contact dermatitis to local anesthetics, which is best diagnosed with the use of patch testing. Generally, people with contact dermatitis to one local anesthetic will tolerate another local anesthetic. Find out more about local anesthetics causing contact dermatitis.