approach to a critically ill patient with an allergy to a cephalosporin Allergy history - Nature of reaction (description & treatment required) - Time from drug exposure to reaction - Time elapsed since reaction - Antibiotics able to tolerate Type II - IV hypersensitivity reaction - Stevens - Johnson syndrome - Acute interstitial nephritis - Drug rash eosinophilia systemic symptoms (DRESS) - Hemolytic anemia - Drug fever - Serum sickness Avoid any beta - lactam (including penicillins, cephalosporin, or even carbapenem). Possible type - I ( IgE - mediated) hypersensitivity reaction Higher risk - Anaphylaxis or angioedema (wheeze, hypotension, syncope, stridor, etc.) - Solid documentation (e.g. repeated events, documented skin test - positive) - Aggressive medical stabilization required Intermediate risk - Urticaria without anaphylaxis/angioedema - Reaction of unknown nature Lower risk - Minor rash not involving hives - Isolated pruritus without a rash Possible treatments - Different cephalosporin with non - cross - reacting R - chain (see matrix)* - Aminopenicillin probably safe if no cross - reacting R - chain? (see matrix ) *** - Nafcillin or piperacillin should be safe - Carbapenem (especially meropenem) ** - Non - beta - lactam antibiotics ** *Generally considered to be safe. However, may consider graded challenge with first dose if history of severe reaction (e.g. anaphylaxis). ** Safe regardless of how scary the original allergic reaction is. *** Little data on this; consider graded challenge or penicillin skin testing if severe reaction. Internet Book of Critical Care by @PulmCrit