Immediate-type hypersensitivity drug reaction 2019-02-24T14:43:10Z Hypersensitivity that is observed within 1 hr of exposures. A variety of adverse reactions can occur within minutes to hours of exposure to a drug. Some can be related to the pharmacological action of the drug (WHO Adverse Reaction Terminology type A for augmented) and usually have a low mortality. Others are not readily predictable based on the structure and pharmacological action of the drug and have a relatively high mortality risk (Type B for bizarre). The most serious form of immediate onset drug hypersensitivity reaction, anaphylaxis. Other reactions including itching, dizziness/light-headedness, nausea, chest discomfort but without any objective skin features, physical signs or physiological compromise. Skin only reactions include generalized erythema, urticaria or angioedema without any sentinel features (see below) of other organ involvement. Hypersensitivity is broadly defined as objectively reproducible symptoms or signs, initiated by exposure to a defined stimulus at a dose tolerated by normal subjects and may be caused by immunologic (allergic) and non-immunologic mechanisms. Immunologic hypersensitivity