Allergy Agents

Allergy Agents Overview

Histamines

• Definition: Chemical mediators involved in immune and inflammatory responses.

• Location: Found in most body tissues.

• Receptor Types:

  • H1 Receptor: Associated with allergic responses.

  • H2 Receptor: Associated with increased gastric acid secretion and pepsin production.

Concentration and Release

• Higher Concentration: Found in tissues exposed to environmental substances, including:

  • Skin

  • Mucosal surfaces of the nose

  • Lungs

  • Gastrointestinal (GI) tract

• Synthesis and Storage:

  • Synthesized and stored in mast cells and basophils.

• Release Triggers:

  • During immediate hypersensitivity reactions and cellular injury.

Effects of H1 Receptor Stimulation

1. Increased Permeability of Capillaries: Leads to edema (swelling).

2. Bronchial Smooth Muscle Contraction: Results in bronchoconstriction.

3. Stimulation of Sensory Peripheral Nerve Endings: Causes pruritis (itching).

4. Stimulation of Vagus Nerve Endings:

   • Produces reflex bronchoconstriction and cough.

Antihistamines

• Mechanism of Action (MOA):

  • Compete for H1 receptor sites, decreasing allergic responses.

  • Optimal Timing: More effective if taken prior to exposure to allergens, allowing drugs to occupy receptor sites before histamine is released.

Uses of Antihistamines

• Allergic Rhinitis:

• Symptoms:

  • Nasal, ocular, and pharyngeal pruritis.

  • Sneezing.

  • Rhinorrhea (runny nose).

  • Lacrimation (tear production).

• Dermatologic Conditions:

  • Acute urticaria (hives)

  • Contact dermatitis.

• Other Uses:

  • Angioedema (swelling of deep layers of skin).

  • Nausea and vomiting (N/V).

  • Sleep aid.

  • Motion sickness.

Adverse Effects

• Incidence Rates: Higher with first-generation antihistamines.

1. Sedation/Drowsiness: Risk increases; advised to take at bedtime (HS); caution for older adults, driving, and operating machinery.

2. Anticholinergic Effects: Include:

   • Dilated pupils.

   • Urinary retention.

   • Dry mouth.

   • Constipation.

Oral Antihistamines

• Common Drugs:

First Generation: Diphenhydramine, Chlorpheniramine

• Second Generation (preferred for allergies due to fewer side effects):

• Fexofenadine, Loratadine

  • Benefit: Typically offer once daily dosing and less sedation.

Intranasal Antihistamines

• Characteristics:

  • More rapid onset of action compared to oral administration.

  • Associated with a bitter taste.

• Examples:

  • Azelastine

  • Olopatadine

Nursing Considerations for Antihistamines

• Safety Monitoring:

  • Monitor for increased sedation following administration.

  • Advise patients not to drive while sedated.

  • Monitor for vision changes (related to anticholinergic effects).

  • Encourage increased hydration for managing dry mouth and constipation.

  • Highlight significant safety issues with first-generation antihistamines.

Intranasal Corticosteroids

• Examples of Medications:

  • Fluticasone

  • Triamcinolone

Mechanism of Action (MOA)

• Inhibit release of inflammatory cytokines.

• Block hypersensitivity response from allergens.

Uses

• Treatment of allergic rhinitis.

Adverse Effects

• Risks include:

  • Epistaxis (nosebleeds).

  • Dryness and burning sensations.

Nursing Considerations

• Educate patients on proper usage methods.

• Advise against as-needed (PRN) use.

• Instruct not to blow nose for one hour following administration.

• Notable effects seen within 5-7 days post-use.

• May be used in combination with antihistamines for enhanced efficacy.

Mast Cell Stabilizers

• Example:

  • Cromolyn (KROE moe lin).

• Use:

  • Administered as a nasal spray for allergic rhinitis; to be used immediately before allergen exposure (15 minutes prior).

Mechanism of Action (MOA)

• Stabilize mast cells and prevent the release of broncho-constrictive and inflammatory substances.

• Adverse Effects: Potential for hoarseness, cough, and unpleasant taste; beneficial for known allergy exposure.