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Hypersensitivity refers to an exaggerated or inappropriate immune response to a substance that is normally tolerated. It encompasses allergic reactions and other non-allergic hypersensitivities.

Allergic hypersensitivity involves an immune response mediated by IgE antibodies. Common allergic reactions include:

  • Skin rashes, hives, itching – caused by IgE-mediated release of histamine from mast cells in the skin.
  • Anaphylaxis – a severe, life-threatening allergic reaction involving multiple organs. It results from massive IgE-mediated release of mediators like histamine, leukotrienes and prostaglandins. Symptoms include swelling of throat and tongue, shortness of breath, low blood pressure, rapid pulse, etc.
  • Rhinitis – inflammation of the nasal passages due to an allergic reaction. Caused by IgE-mediated mast cell activation and release of histamine and other mediators.
  • Asthma – airway inflammation and bronchoconstriction in response to an inhaled allergen. Also IgE-mediated.

Non-allergic hypersensitivities include:

  • Cytotoxic hypersensitivity – immune response causing destruction of cells, mediated by IgG and IgM antibodies or cytotoxic T cells. Can cause conditions like autoimmune hemolytic anemia, thrombocytopenia, etc.
  • Type III hypersensitivity – immune response causing tissue damage by formation and deposition of immune complexes (antibody-antigen complexes). Examples include serum sickness, lupus, rheumatoid arthritis, etc.
  • T cell-mediated hypersensitivity – activated T cells directly attack host cells and tissues. Involved in conditions like contact dermatitis, transplant rejection, etc.

In the case of benperidol, hypersensitivity likely refers to an allergic reaction, specifically a Type I IgE-mediated reaction that could manifest with rash, hives, itching, bronchospasm, or even anaphylaxis upon administration. Due to the risk of such a severe and potentially life-threatening reaction, benperidol is contraindicated in anyone with a known hypersensitivity to the drug. Alternative antipsychotic agents should be used instead.

Overall, hypersensitivity is an unwanted side effect of a drug that can limit its use in certain patients. Care must be taken to monitor for any signs of allergic or adverse reaction, especially when a drug is first administered.

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