A nurse is assessing a client who is taking oxacillin to treat an infection. The nurse should recognize which of the following findings is a manifestation of an allergic reaction?

The correct answer is B: Pruritus. Pruritus, or itching, is a common manifestation of an allergic reaction to medications like oxacillin. Allergic reactions involve the body's immune system responding to a substance it perceives as harmful. Itching is a result of histamine release in response to the allergen. Fever (choice A) is more indicative of an infection rather than an allergic reaction. Amber urine (choice C) can be a sign of dehydration or liver issues, not specifically related to an allergic reaction. Diarrhea (choice D) is more likely a side effect of the medication or an infection rather than an allergic reaction.