A

20-year-old female patient presents to her GP for the second time. Yesterday,

she was prescribed penicillin antibiotics for pneumonia. Unfortunately, by the

next day, an unpleasant, severely itchy rash in the form of small blisters had

popped up on most of her body. This is urticaria, which is a very common form

of allergic reaction. The patient is prescribed other antibiotics and

antihistamines to help relieve the unpleasant symptoms of urticaria. During

this allergic reaction, mediators such as heparin and histamine are shed from

mast cells.