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You are seeing an 8 year old girl who was prescribed an oral cephalosporin antibiotic 1 week ago for rhinitis. She has 3 more days until she finishes the course. Now she has developed an itchy urticarial-like rash, although it is more fixed than urticaria typically are (does not move around nor come and go). She also has some generalized mild arthralgias and a low-grade fever to 100.2 F. 

What is the most effective treatment for this entity?