Allergy to local anaesthetic agents used in dentistry – what are the signs, symptoms, alternative diagnoses and management options?

Following the administration of a local anaesthetic, a minority of patients may suffer one of a range of unwanted symptoms. Some of these symptoms can be mistaken for hypersensitivity or allergy and the patient may be unnecessarily told that he/she is allergic to the anaesthetic; this is not the case in the majority of patients. Mislabelling of patients as allergic to local anaesthetics can lead to problems for dental practitioners with patients unable to undergo routine dental treatment.1

Local anaesthetic agents can be categorized into two classes:

True allergy to an amide local anaesthetic is exceedingly rare. Local anaesthetics of the ester type are more likely to produce allergic reactions as they are metabolized to para-aminobenzoic acid (PABA), which is an allergenic compound.2,3,4 The only ester local anaesthetic used in primary care dentistry is benzocaine, which is used in topical preparations applied prior to administration of local anaesthetic injections. An allergy to one ester local anaesthetic rules out the use of another ester, as the metabolism of all esters yields PABA. Patients are unlikely to show cross-sensitivity to amide local anaesthetics as these are not metabolized to PABA. Allergy to one amide local anaesthetic does not rule out use of another amide local anaesthetic.3,5 However, it would be unwise to use another amide local anaesthetic without hypersensitivity tests5