A nurse is caring for a client who reports having an allergy to penicillin. Which of the following manifestations indicates an allergic reaction to penicillin?

Penicillin allergy is an immune-mediated hypersensitivity reaction that can range from mild skin manifestations to severe life-threatening anaphylaxis. True allergic responses involve activation of the immune system and commonly present with urticaria, angioedema, bronchospasm, or hypotension. It is important for nurses to distinguish allergic reactions from common medication side effects such as nausea or diarrhea. Prompt recognition of serious allergic symptoms is essential to prevent airway compromise and severe systemic reactions. Rationale: A. Nausea is a common gastrointestinal side effect of many antibiotics, including penicillin, but it does not indicate an allergic reaction. It results from irritation of the gastrointestinal tract rather than an immune response. Although uncomfortable, it does not suggest hypersensitivity or anaphylaxis. B. Angioedema is a serious allergic manifestation characterized by rapid swelling of deeper layers of the skin, often involving the lips, face, tongue, or airway. It indicates an immune-mediated hypersensitivity reaction and can quickly progress to airway obstruction. This finding requires immediate recognition and intervention. C. Insomnia is not a typical sign of penicillin allergy and is unrelated to hypersensitivity reactions. It may occur due to stress, illness, or other medications but is not considered an indicator of an allergic response to antibiotics. D. Diarrhea is a common adverse effect of antibiotics caused by disruption of normal intestinal flora. It reflects gastrointestinal intolerance rather than an immune-mediated allergic reaction. Although severe diarrhea may require evaluation, it does not indicate a penicillin allergy.