TWU Pharmacology Exam 1 Practice Test

Type IV hypersensitivity is a delayed, cell-mediated allergic reaction driven by sensitized T lymphocytes rather than antibodies. In the context of drug allergies, it most often shows up as contact dermatitis—an itchy, inflamed rash at the site of contact with the drug or its metabolites that appears after about 24 to 72 hours. This delayed timeframe and the involvement of T cells distinguish it from immediate, antibody-driven reactions.

IgE-mediated reactions (Type I) are immediate and can cause hives, wheezing, or anaphylaxis. Anaphylaxis is an example of a severe Type I reaction. Serum sickness is a Type III reaction, caused by immune complexes and typically presents with systemic symptoms like fever, malaise, arthralgia, and rash.