Final answer:
Para-aminobenzoic acid (PABA) is the metabolite of ester-type local anesthetics most likely to cause a type I hypersensitivity reaction, which involves the release of histamine from mast cells mediated by immunoglobulin E (IgE) antibodies.
Step-by-step explanation:
The metabolite of ester-type local anesthetics (LAs) that is most likely to cause a type I hypersensitivity reaction is Para-aminobenzoic acid (PABA). Type I hypersensitivity is an immediate allergic reaction which can present itself as anaphylaxis, urticaria, angioedema, or asthma. It is mediated by immunoglobulin E (IgE) antibodies, which, upon exposure to an allergen, lead to mast cell degranulation and subsequent release of mediators like histamine.
Ester-type LAs are metabolized into PABA in the plasma, and this metabolite can act as an allergen, provoking a hypersensitivity response in some individuals. This type of allergic reaction can be contrasted with type II hypersensitivity, which involves cytotoxicity mediated by antibodies, and does not typically involve PABA. In clinical settings, LAs are chosen based on their allergic potential, with amide-type LAs having a lower risk of allergy because they do not produce PABA upon metabolism.