The nurse is preparing to give a second dose of trimethoprim-sulfamethoxazole (TMP-SMX) to a patient and notes a petechial rash on the patient's extremities. The nurse will perform which action?

A. Request an order for a blood glucose level: TMP-SMX does not typically cause acute changes in blood glucose, so testing glucose would not clarify the cause of petechiae. Petechial rashes suggest a possible blood dyscrasia such as thrombocytopenia rather than a metabolic disturbance. B. Hold the dose and notify the provider.: A petechial rash can signal a serious hypersensitivity reaction or drug-induced thrombocytopenia. Giving another dose could worsen the reaction and increase the risk of bleeding or systemic complications. Holding the medication and seeking immediate evaluation is the safest intervention. C. Request an order for a BUN and creatinine level.: Although TMP-SMX can affect renal function, petechiae primarily indicate a hematologic problem rather than isolated kidney dysfunction. Checking kidney values does not address the risk for severe allergic or platelet-related complications. D. Request an order for diphenhydramine (Benadryl): Antihistamines can help mild allergic reactions but may mask symptoms of a more serious underlying condition such as thrombocytopenia. Giving it without stopping the medication could delay correct diagnosis and treatment.