The nurse is assisting in the administration of IV vancomycin to a client who has methicillin-resistant Staphylococcus aureus (MRSA). Which of the following findings indicate an allergic reaction to the medication?

A. Urticaria: The appearance of hives (urticaria) is a classic sign of an allergic reaction to medications, including vancomycin. It reflects histamine release and immune hypersensitivity, requiring prompt assessment and possible intervention. B. Hypertension: Vancomycin does not typically cause elevated blood pressure as an allergic response. Blood pressure changes are more likely related to underlying conditions or infusion-related hemodynamic effects, not allergy. C. Headache: Headache is not a typical manifestation of an allergic reaction to vancomycin. It may occur as a nonspecific adverse effect but does not indicate immune-mediated hypersensitivity. D. Tinnitus: Tinnitus is associated with vancomycin ototoxicity at high doses or with prolonged therapy, not an immediate allergic reaction. It reflects potential auditory nerve or cochlear involvement rather than histamine-mediated responses.