Severe delayed hypersensitivity: Implications of cross-reactivity between penicillins and cephalosporins

Avoid all penicillins and cephalosporins in patients with severe delayed penicillin hypersensitivity (eg drug rash with eosinophilia and systemic symptoms [DRESS], Stevens–Johnson syndrome / toxic epidermal necrolysis [SJS/TEN], severe blistering or desquamative rash, significant internal organ involvement [eg acute interstitial nephritis]).

Cross-reactivity between penicillins and cephalosporins is less well described in patients with severe delayed penicillin hypersensitivity than those with immediate hypersensitivity. Rarely, patients may be allergic to the beta-lactam ring structure and not the R1 side-chain.