The antibiotics most commonly associated with allergic reactions are the sulfonamides, penicillins, and cephalosporins. Anaphylaxis is the most severe form of allergic reaction. It can present as an acute, life-threatening reaction with multiple organ system involvement or it can be more localized in appearance. Approximately 1 in every 2,700 hospitalized patients experience drug-induced anaphylaxis. If antibodies are not involved in the process, the reaction is termed anaphylactoid.