N20025: E3: Drugs to Decrease Histamine Effects & Allergic Response

Nursing: Second-generation H1 receptor antagonists

-2nd gen H1 safer for older adults -Caution in renal failure

What are First-generation H1 receptor antagonists used to treat

-Allergic reaction -Motion sickness -Insomnia

Indications for use: Antihistamines

-Allergic rhinitis -Anaphylaxis -Allergic conjunctivitis -Drug allergies, pseudoallergies -Blood/blood product transfusion -Dermatologic conditions

Drug Reactions

-Any drug may cause reaction -Any body tissue may be involved -May occur 7-10 days after initial exposure -Resolves after drug D/C

Type IV Hypersensitivity (Delayed)

-Cell-mediated response -Sensitized T lymphocytes react with antigen to cause inflammation -no antibody looking for antigen = longer response time EXAMPLES -Tuberculin test -Contact dermatitis -Graft rejection

What happens in the allergic response when histamine stimulates its receptors

-Contraction of smooth muscles in respiratory tract (wheezing) -Stimulation of Vagus nerve -Increased permeability of veins & capillaries (edema) -Dilation of capillaries in skin -Increased mucus secretion -Stimulation of peripheral nerve endings -Increase secretion of gastric acid -Increased HR and force

Characteristics of Second-generation H1 receptor antagonists

-Do not readily enter the brain from the blood -Bind preferentially to peripheral rather than central H1 receptors (less CNS effect)

What happens in the allergic response

-Histamine is released in response to stimuli (allergic reactions, cellular injury) -After released, its target cells are in the blood vessels, respiratory & GI tract

What happens to the affected skin in contact dermatitis

-Inflamed, warm, swollen, itchy -Blisters may form, drain, and become infected -Rash in 24 hours after contact

Type III hypersensitivity (Immune Complex)

-Mediated by IgG or IgM -Forms antigen-antibody complexes --> acute inflammatory reaction in tissue EXAMPLE -Serum sickness

Type II hypersensitivity (Cytotoxic)

-Mediated by IgG or IgM -Direct damage to cell surface EXAMPLES -Blood transfusion reactions -HDN, hemolytic anemia -penicillin, heparin reactions

Mild vs severe anaphylaxis

-Mild: itching, rhinitis -Severe: respiratory distress cardiac collapse, life threatening

Sx of allergic rhinitis

-Nasal congestion -Itching, sneezing -Watery drainage -Itching of throat, eyes, ears

Seasonal disease allergic rhinitis

-Response to airborne pollens -Most common in spring/fall -Aka hay fever

Perineal disease allergic rhinitis

-Response to nonseasonal allergens -Dust mites -Molds -Animal dander

What are Second-generation H1 receptor antagonists used to treat

-Seasonal allergic rhinitis -Minor allergies -Itching

Symptoms of drug reactions VARY but may include...

-Skin rash -Itching -Fever -Hematologic or hepatic reactions

Pt Education: Second-generation H1 receptor antagonists

-Take med *before* exposure to allergen -Avoid taking with Alcohol -Avoid accidental OD -Teach proper nasal spray use if needed

Pt education: First-generation H1 receptor antagonists

-Take med *before* exposure to allergen -Tolerance to drowsiness in few days -Avoid taking with Alcohol (CNS -) -Avoid accidental OD

Nursing: First-generation H1 receptor antagonists

-Use caution in older adults (r/t confusion & dizziness) -May thicken secretions

What is the cause of Type I, II, & III hypersensitivity reactions

Antibody molecules

drug-drug interactions of First-generation H1 receptor antagonists

Antidepressants CNS depressants

What is the cause of Type IV Hypersensitivity Reactions

Antigen Specific T Cells

Adverse Effects of First-generation H1 receptor antagonists

CNS depression *drowsiness, sedation Anticholinergic side effects *constipation *retention *dry mouth *blurred vision

When explaining the options for anti-histamines to a patient, the nurse explains that second generation H1 antagonists differ from first generation H1 antagonists by A. Cause greater CNS sedation B. Are available by prescription only C. Are more cost effective D. Do not cross the BBB

D. Do not cross the BBB

Example of First-generation H1 receptor antagonists

Diphenhydramine

Serum Sickness

Excessive antigens combine with antibodies cause tissue damage and immune complexes

T/F Allergic Rhinitis is caused by a type III sensitivity

False, type I

Example of Second-generation H1 receptor antagonists

Fexofenadine loratadine cetirizine

Children may experience paradoxical effect to what drug

First-generation H1 receptor antagonists (they get hyper instead of sleepy)

The first chemical mediator released in the allergic/inflammatory response

Histamine (H1)

What are allergic food reactions

Immune response to ingestion of a protein -i.e. shellfish**, fish, corn, seeds, bananas, egg, milk, soy, peanut, tree nuts *high risk of triggering anaphylaxis

Allergic Rhinitis

Inflammation of nasal mucosa caused by type I reaction to inhaled allergens

Where is histamine (H1) found

Mast cells Basophils

Children may outgrow allergies to...

Milk Eggs Wheat Soy

Contraindications of First-generation H1 receptor antagonists

Narrow angle glaucoma BPH

Action of First-generation H1 receptor antagonists

Occupy same receptors as Histamine which prevents histamine from reaching target

Action of Second-generation H1 receptor antagonists

Occupy same receptors as Histamine which prevents histamine from reaching target

Type I hypersensitivity (Immediate)

Occurs within minutes -IgE induced Mast cell activation (causes histamine release) -Usually after 2nd or later exposure -Anaphylaxis (mild to severe) *antibody for antigen is already inside body

What do First-generation H1 receptor antagonists do

Prevent/reduce most physiologic effects that histamine produces at receptor sites *inhibit smooth muscle constriction in blood vessels, respiratory, GI tract *decrease capillary permeability *decrease salivation and tear formation

2 Types of Allergic Rhinitis

Seasonal Perennial

What drug class is replacing first gen H1

Second-generation H1 receptor antagonists

What meds have a mild beneficial effect in chronic asthma

Second-generation H1 receptor antagonists

The 4 types of hypersensitivity reactions are based on...

The producing mechanism

T/F Histamine is the first chemical mediator released during inflammatory response.

True

What is contact dermatitis

Type IV reaction from direct contact with an antigen i.e. poison ivy, cosmetics, metals

What are Hypersensitivity Reactions caused by

abnormal immune reaction (antibodies recognize the antigen/irritant)

Hypersensitivity Reactions involve an exaggerated...

allergic response

No known preventative for...

food allergies

How does breast feeding affect food allergies

prevent food allergies as a child but increase them as a person ages

Antihistamines relieve ________________ but do not relieve/stop/cure __________________

symptoms hypersensitivity

Hypersensitivity Reactions can cause...

tissue damage & serious illness