WK 4 Histamines: Pathophysiology

Histamines: Pathophysiology

  • Definition of Histamine

    • First chemical mediator released in the immune and inflammatory response.

    • Found in most body tissues, especially concentrated in areas exposed to the environment: eyes, nose, lungs, and gastrointestinal (GI) tract.

  • Where Histamine is Found

    • Stored in various body tissues, particularly in the central nervous system (CNS).

    • Concentrated in tissues that frequently encounter environmental stimuli.

  • Release Mechanism

    • Histamines are discharged in response to specific stimuli such as:

    • Allergic reactions

    • Cellular injury

    • Extreme cold

    • Produces reactions specific to the muscle groups involved in these stimuli.

Effects of Histamines

  • Histamines play a crucial role in the immune and inflammatory responses, leading to a variety of physiological effects dependent on receptor binding and tissue types.

Hypersensitivity (Allergic) Reactions

  • Definition of Hypersensitivity Reaction

    • Also known as an allergic reaction.

    • Characterized by exaggerated responses by the immune system, resulting in tissue injury and potentially serious diseases.

Histamine Antagonists (Antihistamines)

  • Definition of Antihistamine

    • Medications that inhibit the action of histamines by preventing histamine from binding to its receptors, thereby alleviating symptoms associated with excess histamine activity.

Drug Allergies

  • Definition of Allergic Drug Reactions

    • Any drug can induce an immunologic response, leading to hypersensitivity reactions characterized by multiple symptoms that are unpredictable.

    • Can occur 7-10 days after the first exposure.

    • Can occur minutes to hours after subsequent drug exposures.

  • Anaphylaxis Reactions

    • Occur immediately upon exposure to an allergen.

    • Symptoms include:

    • Rash or hives

    • Difficulty in breathing (DIB)

    • Swelling

    • Severity can be life-threatening and may occur on the first exposure to the causative agent, with common triggers such as contrast media used for x-rays.

Drug Therapy: Diphenhydramine (Benadryl)

  • Uses

    • Treatment of hypersensitivity reactions such as allergic rhinitis, conjunctivitis, and dermatitis.

    • Management of motion sickness and insomnia.

    • Treatment of parkinsonism.

  • Mechanism of Action

    • Diphenhydramine does not prevent the release of histamines but rather reduces and prevents the symptoms associated with histamine release, including:

    • Decreasing salivation and tear formation

    • Reducing edema, bronchoconstriction, and itching (pruritus).

  • Adverse Effects

    • CNS depression, causing drowsiness and sedation, or CNS stimulation leading to anxiety and agitation.

    • Anticholinergic effects, including dry mouth and blurred vision.

  • Nursing Considerations

    • Patients can take Diphenhydramine with milk to mitigate GI side effects.

    • It may be taken on an empty stomach or with food, depending on tolerance.

Drug Therapy: Cetirizine (Zyrtec) & Loratadine (Claritin)

  • Uses

    • Provide temporary relief of respiratory allergies and urticaria (hives).

  • Mechanism of Action

    • Binds to histamine receptor sites to prevent histamine activation.

    • These medications do not cross the blood-brain barrier, reducing the incidence of drowsiness.

  • Adverse Effects

    • Potential side effects include drowsiness, headache (HA), dizziness, nausea/vomiting (N/V), and fatigue.

Drug Therapy: Fexofenadine (Allegra)

  • Uses

    • Effective for seasonal allergic rhinitis, minor allergies, and urticaria.

  • Mechanism of Action

    • Prevents the activation of histamine through receptor blockage.

    • Does not cross the blood-brain barrier, hence minimizing drowsiness.

  • Adverse Effects

    • Minor headaches, N/V, dysmenorrhea, and fatigue may occur.

  • Nursing Considerations

    • Avoid consumption of fruit juices as they may decrease the absorption of Fexofenadine.

QSEN ALERT – Safety

  • Monitoring is essential when using MAO inhibitors (MAOIs) within 14 days of antihistamine use due to potential interactions.

Nursing Considerations for Managing Histamine Effects

  • Collect current prescribed, over-the-counter (OTC), and herbal medications from the patient.

  • Conduct a baseline assessment of vital signs (VS).

  • Continuously assess for adverse effects and therapeutic effects, particularly the relief of symptoms associated with histamine and allergic reactions.

  • Post Administration Guidelines

    • Advise patients to avoid alcohol (ETOH) and to take medication as prescribed.

    • Encourage an increase in fluid intake.

Patient Education and Understanding

  • Case Study/Teaching Prompt

    • Engage patients in understanding the adverse effects of Diphenhydramine (Benadryl).

    • Example patient statements include:

    • a) Dry mouth and constipation

    • b) Drowsiness and sedation

    • c) Congestion and stuffiness

    • d) Itching and skin rash

    • e) Rebound congestion

    • f) Hypertension

    • g) Urinary retention

    • h) Blurred vision

    • Understanding which symptoms reflect an awareness of the potential side effects of the medications prescribed.

Conclusion of Nursing Interventions

  • Prioritize assessment for potential hypersensitivity reactions in all patients upon first contact.

  • Ensure patients with known allergies carry identification for their allergies, especially if medication-related.

  • Monitor closely for excessive drowsiness, particularly during the initial days of therapy with antihistamines.

  • Provide support and emergency contact information to families of children who suffer from allergies.