NSG 116 Chapter 32 Flashcards: Drug Therapy for Histamine Effects and Allergic Response

Histamine Pathophysiology and Effects

• Histamines Defined: These are the first chemical mediators released during immune and inflammatory responses.
• Where Histamines are Found:
  • Stored in most body tissues.
  • Present in the Central Nervous System (CNS).
  • Highly concentrated in environmentally exposed tissues such as the eyes, nose, lungs, and Gastrointestinal (GI) tract.
• Histamine Release Triggers: Discharged in response to specific stimuli, including:
  • Allergic reactions.
  • Cellular injury.
  • Extreme cold.
• Result of Histamine Release: Produces reactions specific to the muscle groups involved.
• Key Effects of Histamines:
  • Bronchoconstriction.
  • Cough and/or respiratory distress.
  • Edema.
  • Nasal congestion and increased mucous production.
  • Pruritus (itching).
  • Skin flushing.

Hypersensitivity (Allergic) Reactions

• Definition: These are allergic reactions resulting from exaggerated responses by the immune system.
• Consequences: They produce tissue injury and can lead to serious disease.

Histamine Antagonists (Antihistamines)

• Mechanism: These medications stop the action of histamines by preventing them from binding to their specific receptors.

Drug Allergies and Anaphylaxis Reactions

• Allergic Drug Reactions:
  • Any drug has the potential to induce an immunologic response.
  • These reactions cause hypersensitivity with a variety of symptoms.
  • They are unpredictable.
  • Can occur 7-10 days after the initial drug exposure.
  • Can also manifest minutes to hours after a second exposure to the drug.
• Anaphylaxis Reactions:
  • Occur immediately upon exposure.
  • Symptoms include rash, hives, difficulty inspirating/breathing (DIB), and swelling.
  • Can be life-threatening in severity.
  • May occur even on the very first exposure to a causative agent.
  • Commonly associated with contrast media used in X-rays.

Specific Antihistamine Drug Therapies

Diphenhydramine (Benadryl)

• Uses:
  • Treatment of hypersensitivity reactions (e.g., allergic rhinitis, conjunctivitis, dermatitis).
  • Motion sickness.
  • Insomnia.
  • Parkinsonism.
• Mechanism of Action:
  • Does not prevent the release of histamine.
  • Prevents or reduces most symptoms associated with histamine release.
  • Decreases salivation and tear formation.
  • Decreases edema, bronchoconstriction, and pruritus.
• Adverse Effects:
  • Central Nervous System (CNS) depression, leading to drowsiness and sedation.
  • Alternatively, CNS stimulation can occur, causing anxiety and agitation.
  • Anticholinergic effects (e.g., dry mouth, constipation, urinary retention, blurred vision).
• Nursing Considerations:
  • Can be taken with milk to minimize GI side effects.
  • Can be administered on an empty stomach or with food.
  • QSEN ALERT - Safety! Avoid use within 14 days of taking Monoamine Oxidase Inhibitors (MAOIs).

Cetirizine (Zyrtec) & Loratadine (Claritin)

• Uses:
  • Temporary relief of respiratory allergies.
  • Relief of urticaria (hives).
• Mechanism of Action:
  • Binds to histamine receptor sites to prevent histamine activation.
  • Does not readily cross the blood-brain barrier, which generally results in fewer drowsiness effects compared to first-generation antihistamines.
• Adverse Effects:
  • Drowsiness (though generally less pronounced than with first-generation antihistamines).
  • Headache (HA).
  • Dizziness.
  • Nausea/Vomiting (N/V).
  • Fatigue.

Fexofenadine (Allegra)

• Uses:
  • Seasonal allergic rhinitis.
  • Minor allergies.
  • Urticaria.
• Mechanism of Action:
  • Prevents the activation of histamine.
  • Does not cross the blood-brain barrier, leading to minimal or no drowsiness effects.
• Adverse Effects:
  • Minor headache.
  • Nausea/Vomiting (N/V).
  • Dysmenorrhea (painful menstruation).
  • Fatigue.
• Nursing Considerations:
  • Avoid taking with fruit juice, as it can decrease the absorption of the drug.

General Nursing Considerations for Antihistamine Therapy

Assessment

• Medication History: Obtain a comprehensive list of all current prescribed, over-the-counter (OTC), and herbal medications.
• Baseline Vitals: Establish baseline vital signs (VS).
• Adverse Effects: Continuously assess for any adverse effects of the medications.
• Therapeutic Effects: Monitor for the desired therapeutic effects, specifically the relief of signs and symptoms related to histamine release or allergic reactions.
• Allergy Assessment:
  • Assess the patient's condition in relation to disorders for which antihistamines are used.
  • For patients with known allergies, attempt to identify factors that precipitate or relieve allergic reactions, and note specific signs and symptoms experienced during a reaction.
  • Assess every patient for potential hypersensitivity reactions. When asking about allergies, be specific (e.g.,