Delayed Hypersensitivity Reactions

Delayed hypersensitivity or Type IV reactions (Table 11) are T-cell-mediated, i.e., specifically sensitized CD4+ T-lymphocytes initiate the reactions. Sensitization develops slowly requiring repeated exposures to a specific allergen. Once sensitized, upon reexposure immunologically committed lymphocytes react with the allergen (antigen) and damage tissue by direct toxic effects or through the release of cytokines, which activate eosinophils, monocytes, neutrophils, and macrophages and killer cells.

Table 11. Delayed Hypersensitivity Reaction.

  • Identify at-risk patient
    • A negative history of prior delayed hypersensitivity reaction does not rule out the possibility of a type IV allergic reaction
Signs and symptoms:
  • 6 to 48 hours following exposure to a specific antigen
    • Fever, malaise
    • Pruritus, erythema urticaria
    • Perioral paresthesia
    • Angioedema
    • Wheezing
Emergency response:
  • Patient should assume an upright or semi-reclining position
    • Identify drugs and other potential allergens to which the patient may have been exposed to in the clinical process
      • Verify that the onset of signs and symptoms was after the initiation of pharmacological or clinical intervention
      • Determine the time interval between the initiation of drug therapy or clinical intervention and the onset of signs and symptoms
      • If the patient is still exposed to the suspected allergen, stop its use
    • In the absence of respiratory distress
      • Prescribe diphenhydramine hydrochloride, 25 to 50 mg, PO, q.i.d
        • Arrange supervision of patient for at least 6 hours after the onset of signs and symptoms
          • If the patient develops wheezing
            • Instruct patient or caretaker to immediately activate EMS
Nota bene:
  • Signs of recovery: symptoms subside
  • Signs of deterioration: pruritus, erythema, urticaria, and angioedema worsen; stridor and wheezing progressing to respiratory distress