Before starting antimicrobial therapy, the nurse assesses a patient for possible drug allergy. Which of the following complaints should alert the nurse to a drug allergy?

A. Diarrhea: Diarrhea is a common side effect of antibiotics due to their effect on the gut microbiota, but it is not typically indicative of an allergy. B. Hives or shortness of breath: Hives (urticaria) and shortness of breath are classic symptoms of an allergic reaction. Hives indicate an immediate hypersensitivity reaction, and shortness of breath can indicate a serious allergic reaction such as anaphylaxis. These symptoms warrant caution and further assessment before starting antimicrobial therapy. C. Headaches: Headaches can be a side effect of various medications but are not a specific sign of a drug allergy. D. Nausea: Nausea is a common side effect of many medications, including antibiotics, but it does not specifically indicate an allergic reaction.