Clavulanic acid, an inhibitor of beta- lactamases, is widely used for antimicrobial therapy in association with beta-lactam antibiotics. Despite this, very few adverse reactions to the molecule have been described so far.
We report a case of not-immediate reaction to clavulanic acid in a young adult who previously tolerated it. The patient complained of generalized itchy erythema two days after completing a course of amoxicillin-clavulanate therapy, and had no previous clinical history of adverse reactions to drugs. Intradermal and skin prick tests with beta-lactam determinants were negative, as well as the oral tolerance test with amoxicillin. Since no commercial preparation of clavulanic acid alone is available, we performed intradermal and skin prick test with the association amoxicillin-clavulanate, that elicited a delayed (24 and 48 hours) response. IgE-mediated reactions to clavulanic acid are rare, since this molecule is poorly allergenic. Based on the onset time and the specificity of the response we hypothesize that a delayed (possibly T-cell mediated) reaction has occurred.

Key words: Clavulanic acid, amoxicillin, beta-lactams, drug reaction.