Reactions to local anaesthetics are often reported, but given how often they are used, most turn out not to be allergic but rather toxic (eg to parabens or sulphite preservative) or autonomic. Where allergy is confirmed, it is often of a delayed hypersensitivity type eg 24-72 hours after exposure. Beware latex allergy and C1 esterase inhibitor deficiency too. Local anaesthetics come in 2 main groups, the esters (procaine, benzocaine) and the amides (lidocaine, bupivocaine). Cross-reactivity is common among the esters but not among the amides or between the 2 groups. Neomycin sensitivity may contribute to a reaction.
Testing can be done with preservative containing products, although a higher rate of false positives may be found. Skin prick testing should be done to non-adrenaline containing products, else reaction is impaired. There can be discordance between patch testing and intradermal testing. The final step should be subcut testing, perhaps blinded (Contact Dermatitis. 59(2):69-78, 2008 PMID 18759873 ).
Suxamethonium sensitivity (where apnoea persists for half an hour or more) – is due to cholinesterase deficiency. Homozygotes will always be sensitive to suxamethonium. Heterozygotes may be sensitive, especially if pregnant, when cholinesterase levels drop further. Testing usually offered to 1st degree relatives of homozygotes (done in Bristol). Children tend to have higher levels so avoid testing unless procedure required (and you may have to retest after puberty).