Reviews
Approach to Patients With Suspected Hypersensitivity to Local Anesthetics

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ABSTRACT

Adverse reactions to local anesthetics are relatively common, but true IgE-mediated hypersensitivity is extremely rare. Fortunately, the vast majority of adverse reactions occur via nonimmunologic means, but considerable confusion still exists among providers. We conducted a review of the literature to determine if earlier estimates of IgE-mediated allergy are consistent with current reports and whether current management strategies are consistent with these findings. We identified several confounding variables involved in the evaluation, including the roles of preservatives/additives, epinephrine, latex, and inadequate testing procedures. These problems may cause significant diagnostic challenges for clinicians. It is in fact much more likely that there is an alternate diagnosis, and in many cases clinicians can begin the evaluation in the office. When local anesthetic allergy is still suspected, the patient should be referred to an allergist for testing to determine if the suspected culprit drug can be safely used, or, if necessary, identify a suitable alternative.

Section snippets

Classification of Types of Adverse Reactions to Local Anesthetics

Any patient who presents with a history of an allergic reaction to local anesthetics should be carefully questioned to determine the nature of the reaction. A patient may have been advised that he/she is allergic to one of these drugs without ever receiving a proper evaluation. Differentiating between local anesthetic hypersensitivity and other causes of adverse reactions can be difficult because systemic symptoms such as dyspnea, swelling, and light-headedness may occur by multiple mechanisms.5

Mechanism of Action of Local Anesthetics and Local Reactions

As an action potential reaches a particular nerve cell, the sodium channels open and sodium ions flood the cell, causing depolarization. The gate that regulates passage of sodium ions is on the cytoplasmic side of the cell, and, when open, is susceptible to the binding of local anesthetics. These compounds keep the channel inactive and block further depolarization; this interruption of conduction is termed conduction block.7 Local anesthetics are injected into the subcutaneous tissue where they

Psychosomatic Responses

Psychosomatic responses are the most common adverse reaction and appear to be more common in dental procedures.9 This may be related to the general anxiety some patients have in the dentist’s chair. Regardless, anxiety may lead to dyspnea, hyperventilation, and other sympathetic responses, including tachypnea, tachycardia, diaphoresis, and hypertension. Some patients have reported other more nebulous symptoms such as peripheral and/or circumoral paresthesias, which do not occur with true

Immunologic Reactions in Drug Allergy

Anaphylaxis refers to type I hypersensitivity reactions (in Gell and Coombs nomenclature) and are the most immediately life-threatening. When antigen binds to preformed IgE antibodies on the surface of mast cells in sufficient quantities to cross-link 2 or more antibodies, a signal is transmitted into the cell that causes degranulation.11 This process releases potent intracellular inflammatory mediators including histamine, leukotrienes, cytokines, and proteases.12 The result is a constellation

Cross-Reactivity

Local anesthetics are composed of an aromatic ring connected to a tertiary amine via an amide- or ester-bonded intermediate chain. They are classified as amides or esters on the basis of this bond7 (Table 2). The vast majority of reported allergic reactions in the literature have been to ester-bonded agents, which are derivatives of PABA, a known allergen. This allergenicity has led to the near-exclusive use of the newer amide-bonded agents in clinical situations. Cross-reactivity does occur

Management of Patients with Suspected Allergy to Local Anesthetics

When a patient presents to the office after the event and gives a history of an untoward reaction to a local anesthetic, the first step is to obtain a careful history. Past medical records should be reviewed in an attempt to identify the agent and the concentration under which it was used. The time interval between administration and the onset of symptoms and the specific symptoms reported should also be queried. If obtainable, this information will allow discrimination between psychosomatic,

Discussion

The recommended algorithm for treatment of patients with possible local anesthetic allergy has undergone some modification in recent years. Recent literature has raised questions about the efficacy of skin testing because the prevalence of false-positives is as high as 10% to 36% of subjects.2., 31. These may occur in patients with no previous local anesthetic reactions, especially when high concentrations of undiluted local anesthetics are injected intradermally.32 This probably is due to an

Conclusion

This review supports the opinion that type I hypersensitivity (IgE-mediated) reactions to local anesthetic agents are extremely rare. The reported cases in the literature are difficult to objectively analyze and may represent true allergy, false-positives, or anaphylactoid reactions in sensitive persons. In the latter individuals, local anesthetics may be capable of initiating mast cell degranulation, which leads to symptoms and physical signs that mimic an IgE-mediated allergic reaction. When

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    Copyright © 2007 Southern Society for Clinical Investigation. Published by Elsevier Inc. All rights reserved.