Nonallergic Drug Hypersensitivity Reactions

<b><i>Background:</i></b> Nonallergic drug hypersensitivities, also referred to as pseudoallergic or anaphylactoid reactions, have clinical manifestations that are often indistinguishable from allergic reactions. <b><i>Methods:</i></b> We performed a PubMed search using the terms ‘drug allergy, drug hypersensitivity, pseudoallergies, anaphylaxis and nonallergic drug reactions’ and reviewed 511 publications dated between 1970 and 2012. A total of 160 papers that were relevant to the most common nonallergic drug hypersensitivity reactions were selected for discussion. <b><i>Results:</i></b> Nonallergic drug hypersensitivities do not involve either IgE-mediated (type 1) or delayed (type 4) hypersensitivity. Nonallergic hypersensitivities are commonly referred to as pseudoallergic or idiosyncratic reactions. The common nonallergic drug hypersensitivities are secondary to chemotherapeutic drugs, radiocontrast agents, vancomycin, nonsteroidal anti-inflammatory agents, local anesthetic reactions and opiates. Protocols for skin testing of radiocontrast, nonsteroidal anti-inflammatory agents, local anesthetics and chemotherapeutic agents have been developed, though most have not been validated or standardized. Other diagnostic tests include in vitro-specific IgE tests, and the current ‘gold’ standard is usually an oral challenge or bronchoprovocation test. In the case of aspirin, even though it is not believed to be IgE-mediated, a ‘desensitization’ protocol has been developed and utilized successfully, although the mechanism of this desensitization is unclear. <b><i>Conclusions:</i></b> Diagnostic methods exist to distinguish allergic from nonallergic drug hypersensitivity reactions. The best option in nonallergic drug hypersensitivity is avoidance. If that is not possible, premedication protocols have been developed, although the success of premedication varies amongst drugs and patients.