Anaphylactoid reactions local anaesthetics

Allergic reactions are characterised by cutaneous lesions, urticaria, edema or anaphylactoid reactions may occur as a result of sensitivity to local anaesthetic agent. 

Most anaphylactoid reactions are due to a direct or chemical release of histamine, and other mediators, from mast cells and basophils. Immune-mediated hypersensitivity reactions have been classified as types I-IV. Type I, involving IgE or IgG antibodies, is the main mechanism involved in most anaphylactic or immediate hypersensitivity reactions to anaesthetic drugs. Type II, also known as antibody-dependent hypersensitivity or cytotoxic reactions are, for example, responsible for ABO-incompatible blood transfusion reactions. Type III, immune complex reactions, include classic serum sickness. Type IV, cellular responses mediated by sensitised lymphocytes, may account for as much as 80% of allergic reactions to local anaesthetic. 

Anaphylactoid reactions are very rare with amide local anaesthetics and some of those reported have been due to preservatives. Most reported reactions to amide local anaesthetics are due to co-administration of adrenaline (epinephrine), intravascular injection or psychological effects (vasovagal episodes). Reactions with ester local anaesthetics are more common. 

The leucocyte histamine release test (referred to in greater detail in Chaps. 1-7) is one of the in vitro correlates of immediate allergy which may find useful application in investigating reactions to local anaesthetics. It is of some value in detecting acute reactions, whether they are truly anaphylactic or due to direct (non-immune) histamine release (anaphylactoid). It is also more accurate (quantitative), more reliable and more predictive than skin tests, and above all it is free from risk. 

It is not totally inconceivable that in predisposed subjects, local anaesthetics may cause an anaphylactoid reaction via direct conversion of the third complement in the same way as may occur with certain anaesthetic induction agents (discussed elsewhere). 

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See also in sourсe #XX -- [ ]

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