Background: Adverse drug reactions to local anesthetics are frequently reported. However, little is known about the underlying mechanisms. Therefore we investigated 177 patients with a history of 197 events after application of these drugs.

Methods: The diagnostic approach included prick and intracutaneous tests, provocative challenge tests with causative and unrelated local anesthetics, and in selected cases, radioimmunoassays to detect specific IgE. In addition, tests were performed with preservatives, including sodium metabisulfite and parahydroxybenzoic acid ester.

Results: Results of prick and intracutaneous tests with local anesthetics were all negative. Only three patients reacted after subcutaneous challenge with the causative drug (local anesthetics of the amide type). Although one patient showed a delayed-type response to mepivacaine, two patients had immediate-type reactions to articaine and lidocaine. However, in both cases no specific IgE could be detected. In five patients with positive skin test reactions to preservatives, challenge test results remained negative.

Conclusions: Two immediate-type reactions were not IgE-mediated. In only one of 197 reported adverse reactions were we able to prove delayed-type allergic response. Therefore true allergic reactions caused by local anesthetics are extremely rare.