Allergic reactions to ampicillin. Studies on the specificity and selectivity in subjects with immediate reactions

Background and Objective Ainpicillin (AMP) is a drug that has been prescribed extensively. Reactions that have been reported include exanthema. desquamative contact eczema, urticaria and anaphylaxis. Experimental evidence indicates that the side chain of AMP is a structure that may induce a selective immune response either at the humoral or lymphocyte T-cell level. With regard to IgE reactions, the selectivity and specificity of the response needs to be studied in humans. Objective To study tbe specificity of tbe IgE response in a group of subjects who had an immediate allergic reaction after the administration of AMP. Methods Subjects developing an immediate response (anapbylaxis or urticaria) after the administration of AMP or an aminopenicillin derivative witb the same side chain as AMP were studied. Skin tests were made to determinants generated from benzyl penicillin (BP): benzyl penicilloyl (BPO) and minor determinant mixture (MDM), as well as amoxicillin (AX) and AMP. Specific IgE antibodies were determined to benzyl penicilloyl polylisine (BPO-PLL), amoxicilloyl-polyllsine (AX-PLL) and ampicilloyl-polylisine (AMPPLL). The specificity of the IgE antibody response was studied by RAST and RAST inbibition. Subjects were classified in three categories: group A: those who were skin test and/or RAST positive to determinants derived from benzylpenicllin, group B: those who were negative to determinants derived from benzylpenicillin but were skin lest and/or RAST positive to determinants derived from AX and AMP and group C: those who were exclusively positive to determinants derived from AMP. Results A total of 48 subjects was included in the study. In group A there were 35 cases, in group B 10 cases, and in group C tbree cases. RAST inhibition studies showed that in some instances tbe side chain of AMP could induce specific responses with a variable degree of crossreactivity between BP and AX. Conclusions Atbough AMP can induce an immediate IgE response in subjects allergic to betalactams and tbe structure of the side chain may contribute to the specificity of the response, our results indicate tbat in most instances crossreactivity with the other penicillins exists and that in the groups studied selective reactions to just AMP derived determinants were uncommon.