This type of allergic reaction is very rare, but it exists. Symptoms can occur very rapidly, in minutes, following injection of the local anesthetic, or as a late reaction, up to 24 hours later. These can be localized or generalized hives or oedema, anaphylactic shock, loss of consciousness or, in rare cases, death.
The history will distinguish whether the reaction is allergic, or another type of reaction, e.g. toxic, vagal or of intolerance.
In case of doubt, the patient is considered having had an allergic reaction to local anesthetics. Physicians and dentists will not want the patient to get drugs pertaining to that family and will have to undergo all sorts of painful procedures without a local anesthetic.
Skin tests and challenges are done not so much to identify the product that caused the reaction, but rather to find a suitable local anesthetic that the patient could safely tolerate.
An allergy specialist will be able to determine, using progressive skin tests as well as challenges with increasing increments of the drug, if the patient is or is not allergic to the anesthetic tested. By knowing the different types of products used as local anesthetics and the cross-reactions between them, the allergist will be able to choose the appropriate agent for the test.
Once the local anesthetic is identified as safe, physicians and dentists will be able to use it without any fear of reaction because in the final challenge test the dosage used is equivalent to the one most physicians and dentists use to obtain the anesthetic effect.
General anesthetics
Allergic reactions that occur during general anesthesia are very rare. They are due either to antibiotics, one of the drugs used to anesthetize the patient, or by contact with latex, in the form of surgical gloves, endo-tracheal tubes, or catheters, etc. Occasionally, a reaction may be due to the contrast media used for x-rays taken in the operating room. Reactions vary from urticaria to asthma to anaphylaxis, and frequently occur rapidly and may be severe.
To get to the culprit, a complete list of the drugs given the patient is needed. Allergy skin tests can be performed to certain antibiotics, to latex and most drugs used for general anesthesia. It is important to stress that proper concentrations of the drugs tested be used because the results can be non allergic reactions or false positives.
If the causative agent is identified by skin tests, treatment is obviously avoidance if subsequent surgery is needed. A Medic-Alert bracelet should be worn by the patient to identify the allergy. If skin tests are negative, and the patient needs subsequent general anesthesia, he/she must be premedicated with Prednisone and Benadryl at appropriate dosage before surgery. With this protocol, the patient is assured of more than 90% protection, and if he/she does have a reaction, it will be slight.
(translation done by John Weisnagel, M.D.)