When drug reactions resembling allergy occur, they are called drug hypersensitivity reactions (DHRs) before showing the evidence of either drug-specific antibodies or T cells.
DHRs may be allergic or nonallergic in nature, with drug allergies being immunologically mediated DHRs. These reactions are typically unpredictable. They can be life-threatening, may require or prolong hospitalization, and may necessitate changes in subsequent therapy.
Classification of adverse reactions to drugs, using the "SOAP III" mnemonic (click to enlarge the image).
Both underdiagnosis (due to under-reporting) and overdiagnosis (due to an overuse of the term ‘allergy’) are common.
A definitive diagnosis of such reactions is required in order to institute adequate treatment options and proper preventive measures.
Misclassification based solely on the DHR history without further testing may affect treatment options, result in adverse consequences, and lead to the use of more-expensive or less-effective drugs, in contrast to patients who had undergone a complete drug allergy workup.
International Consensus on drug allergy - Demoly - 2014 - Allergy - Wiley Online Library http://buff.ly/1oub3wy