Allergy to Local Anaesthetics

Scenario:

A 68-year old patient comes to the emergency with lacerations on the forearm. You are the doctor on call and decide to suture the laceration using a local anaesthetic. Patient gives history of being "allergic" to Lidocaine. What are your options?

When a patient gives a history of being "allergic" to a medication, even in the absence of proper documentation of a reaction, it is hard to dismiss the claim. Fortunately, true allergic reaction to local anaesthetic is rare. However, "adverse" reactions (local anaesthetic overdose, fainting) appear to be common. Differentiating between allergic and adverse reactions is often difficult because of the similarity of the symptoms. Thus many physicians are conservative and label patients as "allergic" to all "-caine" drugs even when the signs and symptoms are consistent with an adverse reaction. Sadly this can result in the patient being denied the benefit of a local anaesthetic when desireable.

Local anaesthetics are grouped, depending on their chemical structure, into two categories. The "ester" group - cocaine, procaine, cholroprocaine, tetracaine and "amide" group - lidocaine, bupivacaine, etidocaine, mepivacaine, ropivacaine. (Tip: All amide drugs have two 'i's in their spelling, e.g. Lidocaine)

The "esters" are derivatives of para-aminobenzoic acid, which is known to be allergenic in nature and hence it is not unusual that a certain percentage of the population demonstrate allergic reactions to this group of drugs. With the introduction of the "amide" type of local anaesthetics there was a marked drop in allergenic reactions. It should however be remembered that multidose vials of the amide group of drugs e.g. lidocaine, bupivacaine may contain the preservative methylparaben, a chemical similar in structure to paraminobenzoic acid, and hence cause allergic reactions. The other source of antigen is metabisulfite which is present in epinephrine containing local anaesthetic solutions. Cross-sensitive reactions are possible because many other drugs, foods an beverages contain preservatives such as metabisulfites and hydroxybenzoates. Two patients who were suspected of having allergy to local anaesthetics were, on challenge testing, found to have allergies to benzoate and metabisulfite.

When a patient presents with a history of allergy to a local anaesthetic the first step would be to ascertain the signs and symptoms of the reaction. It is, as noted above, difficult to distinguish on occasions if the patient has had an adverse reaction or a true allergic reaction. the other important factor is toxicity arising either from large amounts of local anaesthetic used (e.g. liposuction etc.) or the inadvertent intravascular injection of a local anaesthetic.

In patients where it is deemed that use of local anaesthetic may be a better choice, the next step would be to do a progressive challenge with dilute solution (1:1000) and then undiluted intradermal injection of local anaesthetics to diagnose allergy to the agent. It goes without saying that all necessary resuscitation equipment be at hand, intravenous access be obtained prior to testing, and trained help available. It is prudent to use preservative free solution of the local anaesthetic for the challenge.

Fisher et al¹ conducted a study to determine the incidence of true local anaesthetic allergy in patients with an alleged history of local anaesthetic allergy and whether subsequent exposure to local anaesthetics was safe. Two hundred and eight patients with a history of allergy to local anaesthetics were referred over a twenty-year period to their Anaesthetic Allergy Clinic at the Royal North Shore Hospital, Sydney, Australia. In this open study, intradermal testing was performed in three patients and progressive challenge in 202 patients. Four patients had immediate allergy and four patients delayed allergic reactions. One hundred and ninety-seven patients were not allergic to local anaesthetics. In 39 patients an adverse response to additives in local anaesthetic solutions could not be excluded. In all but one patient local anaesthesia had been given uneventfully subsequently. They contend, "a history of allergy to local anaesthesia is unlikely to be genuine and local anaesthetic allergy is rare. In most instances it can be excluded from the history and the safety of local anaesthetic verified by progressive challenge."

After a Medline search of articles published (over the period 1985-1996) on allergy to local anaesthetics, Egglestone et al² suggested the following recommendations concerning the appropriate use of local anaesthetics and alternative therapies in patients with documented local anaesthetic reactions. "A true immunologic reaction to a local anaesthetic is rare. Patients who are allergic to ester local anaesthetics should be treated with a preservative-free amide local anaesthetic. If the patient is not allergic to ester local anaesthetics, these agents may be used in amide-sensitive patients. In the rare instance that hypersensitivity to both ester and amide local anaesthetic occurs, or if skin testing cannot be performed, then alternative therapies including diphenhydramine, opiods, general analgesia, or hypnosis can be used."

In all instances where local anaesthetics are employed proper patient monitoring, meticulous technique, functioning resuscitative equipment and trained help will go a long way in providing a safe and pain free environment at a relatively low cost in the ambulatory setting.

- Suhas Kalghati

Thanks to Dr. Vijay Guttumukkala, Anaesthesiologist at St. Martha's Regional Hospital in Antigonish for reviewing the draft copy of this article.

1. Alleged Allergy to Local Anaesthetics Fisher MM, Bowie CJ Anaesth Intensive care 1997 Dec;25(6):611-4
    
   
2. Understanding Allergic reactions to Local Anaesthetics Eggleston ST, Lush LW Ann Pharmacotherapy 1996 Jul-Aug;30(7-8)851-7

This page last updated June 19, 2000