Review Question - QID 104256

This patient is presenting with urticaria and pruritus without signs of anaphylaxis such as difficulty breathing, swallowing, or swelling. It can be treated with discontinuation of the offending agent and administration of an antihistamine.

Mild drugs reactions are typically a type I hypersensitivity reaction, mediated by IgE antibodies. Following an initial exposure, B cells produce IgE antibodies that bind to and sensitize mast cells. Upon a subsequent antigen exposure, mast cells degranulate, releasing a variety of vasoactive substances such as histamine, leukotrienes, and prostaglandins. These substances cause a variety of clinical symptoms ranging from urticarial rashes to anaphylaxis. In mild cases, the offending drug should be withdrawn immediately. Mild skin symptoms can be treated with antihistamines such as diphenhydramine. Anaphylaxis is diagnosed when 2 or more organ systems are involved in the reaction, or any reaction causing hypotension. Anaphylaxis should be treated immediately with intramuscular epinephrine.

Schaefer et. al review the diagnosis and management of urticaria. They describe the pathophysiology and discuss some of the common triggers. They recommend the use of diphenhydramine for the treatment of acute urticaria.

Figure A demonstrates a patient with a classic-appearing, urticarial rash. Note the well circumscribed, edematous, wheal-like lesions.

Incorrect Answers:
Answer 1: Cefazolin is utilized for the treatment of skin and soft tissue infections such as cellulitis. This patient's rash is not consistent with cellulitis, which is generally characterized by erythema, warmth, and pain.

Answer 2: Clotrimazole is used for the treatment of cutaneous dermatophyte infections, such as tinea corporis. This patient's rash and clinical presentation are not consistent with a dermatophyte infection.

Answer 4: Epinephrine is used for the treatment of acute anaphylaxis. While urticaria is often present in patients with anaphylaxis, this patient lacks other features of anaphylaxis such as hypotension, bronchoconstriction, or gastrointestinal distress.

Answer 5: Montelukast is an oral leukotriene antagonist that is sometimes utilized in the management of asthma and allergic conditions. It is not indicated in the management of acute allergic reactions.

Bullet Summary:
Acute urticaria without other signs and symptoms suggesting anaphylaxis is managed with antihistamines such as diphenhydramine.