CLINICAL CROSS-REACTIVITY BETWEEN AMOXICILLIN AND CEPHADROXIL IN PATIENTS ALLERGIC TO AMOXICILLIN AND WITH GOOD TOLERANCE OF PENICILLIN

In recent years, patients allergic to amoxicillin (AX) but with good t olerance of penicillin G (PG) have been described. It has been suggest ed that the epitope implicated in this type of sensitization might be located on the side-chain of the AX molecule. Thus, cross-reactivity b etween AX and cephadroxil (CEPH), a cephalosporin which shares an iden tical sidechain with AX, is suspected. This study aimed to demonstrate clinical cross-reactivity between AX and CEPH in patients allergic to AX and showing good tolerance of PG. In 76 of 576 subjects with suspe cted allergic reaction to PG and/or AX, the diagnosis of allergy was c onfirmed. All of these had specific IgE to PG, penicillin V, or AX, an d/or positive skin tests to PPL (penicilloyl-polylysine), or MDM (mino r determinant mixture), or PG, or AX, and/or positive challenge tests with PG and/or AX. Sixteen subjects (21%) allergic to AX (11 with posi tive skin test and five with positive challenge test to AX) and good t olerance of PG (all with negative parenteral challenge test) were sele cted. These 16 patients were subsequently challenged with CEPH (up to 500 mg). Fourteen patients tolerated CEPH, and two (12%) had an immedi ate allergic reaction. Our study indicates that allergy to the side-ch ain of aminopenicillins seems to have little clinical relevance in pat ients with allergic reactions to aminopenicillins but with good tolera nce of PG, as 88% of patients with this clinical characteristic tolera te a cephalosporin which shares an identical side-chain. It seems that IgE from most of these patients recognizes an epitope different from the side-chain and the beta-lactam ring.