RT Journal Article T1 Penicillin and cephalosporin cross-reactivity: role of side chain and synthetic cefadroxil epitopes A1 Bogas, Gador A1 Mayorga, Cristobalina A1 Martín-Serrano, Ángela A1 Fernández-Santamaría, Rubén A1 Jiménez-Sánchez, Isabel M. A1 Ariza, Adriana A1 Barrionuevo, Esther A1 Posadas, Teresa A1 Salas, María A1 Fernández, Tahía Diana A1 Torres, María José A1 Montañez, María Isabel K1 Amoxicillin K1 Betalactam K1 Cephalosporin K1 Cross-reactivity K1 Drug allergy K1 Antigenic determinant K1 Specific IgE K1 Amoxicilina K1 Beta-lactamas K1 Cefalosporinas K1 Hipersensibilidad a las Drogas K1 Reacciones cruzadas K1 Epítopos K1 Inmunoglobulina E AB BackgroundAnalysis of cross-reactivity is necessary for prescribing safe cephalosporins for penicillin allergic patients. Amoxicillin (AX) is the betalactam most often involved in immediate hypersensitivity reactions (IHRs), and cefadroxil (CX) the most likely cephalosporin to cross-react with AX, since they share the same R1 side chain, unlike cefuroxime (CO), with a structurally different R1. We aimed to analyse cross-reactivity with CX and CO in patients with confirmed IHRs to AX, including sIgE recognition to AX, CX, CO, and novel synthetic determinants of CX.MethodsFifty-four patients with confirmed IHRs to AX based on skin test (ST) and/or drug provocation test (DPT) were included. Serum sIgE to AX and benzylpenicillin was determined by Radioallergosorbent test (RAST). Two potential determinants of CX, involving intact or modified R1 structure, with open betalactam ring, were synthesised and sIgE evaluated by RAST inhibition assay.ResultsTolerance to CX (Group A) was observed in 64.8% cases and cross-reactivity in 35.2% cases (Group B). Cross-reactivity with CO was only found in 1.8% cases from Group B. ST to CX showed a negative predictive value of 94.6%. RAST inhibition assays showed higher recognition to CX as well as to both synthetic determinants (66% of positive cases) in Group B.ConclusionsCross-reactivity with CX in AX allergic patients is 35%, being ST not enough for prediction. R1, although critical for recognition, is not the unique factor. The synthetic determinants of CX, 1-(HOPhG-Ser-Bu) and 2-(pyrazinone) are promising tools for determining in vitro cross-reactivity to CX in AX allergic patients.BackgroundBetalactams (BLs) are the drugs most frequently involved in immediate (IgE-mediated) hypersensitivity reactions (IHRs) [1,2,3], which could be explained by their ability to act as haptens due to their high chemical reactivity against proteins [4, 5]. BL chemical structure is formed by a 4-membered ring (the so-called BL ring) that in penicillins is fused to a 5-membered thiazolidine ring, and in cephalosporins to a 6-membered dihydrothiazine ring (Fig. 1). These drugs have a side chain (R1) bound to the BL ring; besides, cephalosporins have a second side chain (R2) bound to the dihydrothiazine ring, whose chemical structures distinguish the different compounds [6, 7]. PB BioMed Central (BMC), Springer Nature YR 2020 FD 2020-12-04 LK http://hdl.handle.net/10668/3574 UL http://hdl.handle.net/10668/3574 LA en NO Bogas G, Mayorga C, Martín-Serrano Á, Fernández-Santamaría R, Jiménez-Sánchez IM, Ariza A, et al. Penicillin and cephalosporin cross-reactivity: role of side chain and synthetic cefadroxil epitopes. Clin Transl Allergy. 2020 Dec 4;10(1):57 DS RISalud RD Apr 17, 2025