Drug-induced urticaria and angioedema occur due to a variety of mechanisms and are characterized clinically by transient wheals and larger edematous areas that involve the dermis and subcutaneous tissue (angioedema). In some cases, cutaneous urticaria/angioedema is associated with systemic anaphylaxis, which is manifested by respiratory distress, vascular collapse, and/or shock.
Causes
IgE-mediated urticaria: Lesions result from antigen-induced release of biologically active molecules (leukotrienes, prostaglandins) from mast cells or basophilic leukocytes sensitized with specific IgE antibodies (type I, anaphylactic hypersensitivity). Mediators released increase venular permeability, modulate the release of biologically active materials from other cell types. In sensitized individuals, a very small amount of drug can trigger a serious reaction. Parenteral administration of the drug in a sensitized individual is much more likely to trigger anaphylaxis than oral administration. Urticaria can be immediate or accelerated, depending on whether IgE molecules are present before drug exposure or are formed during exposure. In complement-mediated urticaria, complement is activated by immune complexes, leading to the release of anaphylatoxins, which, in turn, induce mast cell degranulation. Intolerance to salicylates is presumably mediated by abnormalities of the arachidonic acid pathway.
Symptoms
- Skin redness
- Blueness of the skin (cyanosis), including the lips or nail beds
- Hives and generalized itching
Other symptoms can include hives, a sensation of warmth, asthma symptoms, swelling of the mouth and throat area, difficulty breathing, vomiting, diarrhea, cramping, a drop in blood pressure, and loss of consciousness.
Diagnosis
Clinical diagnosis, at times confirmed by histologic findings.
Treatment
The offending drug should be identified and withdrawn as soon as possible.
Prevention Previously Sensitized Individuals The patient should carry information listing drug sensitivities (wallet card, bracelet).
Radiographic Contrast Media Avoid use of contrast media known to have caused prior reaction. If not possible, pretreat patient with antihistamine and prednisone (1 mg/kg) 30 to 60 min before contrast media exposure.
Treatment of Acute Severe Urticaria/Anaphylaxis Epinephrine .3 to .5 mL of a 1:1000 dilution subcutaneously, repeated in 15 to 20 min. Maintain airway. Intravenous access.
Antihistamines H1 blockers or H2 blockers or combination.
Systemic Glucocorticoids Intravenous Hydrocortisone or methylprednisolone for severe symptoms.
Oral Prednisone, 70 mg, tapering by 10 or 5 mg daily over 1 to 2 weeks, is usually adequate.
Prevention
- Avoid wearing sandals or walking barefoot in the grass if you’re allergic to insect stings.
- Occasionally, people who have a history of drug allergies may safely be given the offending medication after pretreatment with corticosteroids (prednisone) and antihistamines (diphenhydramine).
References