Mr. Carter has been recently started on an antibiotic, and has developed a rash and pruritis. You suspect an allergic reaction and immediately assess him for other more serious symptoms. What question would be most important to ask Mr. Carter?

A. "Have you noticed any blood in your stool?" While this could be a symptom of a severe reaction, it's not the most immediate concern for an allergic reaction. B. "Are you having difficulty with your hearing?" Hearing problems are not typical symptoms of an antibiotic allergy. C. "Do you have a headache?" Headaches can occur with various conditions, including allergic reactions, but it's not the most concerning symptom in this case. D. "Are you having any difficulty breathing?" Difficulty breathing can be a sign of a severe allergic reaction (anaphylaxis) and requires immediate intervention. This is the most critical symptom to assess for.