Drug challenges and desensitization protocols can be of great value to patients who require medications that have previously caused allergic reactions. In the case of penicillin or cephalosporin allergy, it is possible to identify patients at high risk of an immediate hypersensitivity reaction because of the presence of anti-penicillin IgE antibodies that are directed to the β-lactam ring structure. 26,30 Conversely, if IgE antibodies to penicillin major and minor determinants are absent, the incidence of an immediate hypersensitivity reaction on administration of β-lactam antibiotics approaches 1% or less. 30 Desensitization protocols can be separated into true immunologic desensitization, in which IgE antibodies are bound to the medication, and test-dosing regimens, in which risk of a repeated allergic reaction is high, but no in vitro or in vivo tests are available to verify or monitor the presumed immunologic sensitivity. 26 In the case of radiographic contrast material idiosyncrasy, pretreatment medications combined with the use of lower osmolality radiographic contrast media have helped to reduce the risk of repeated immediate generalized reactions. 19