Chapter 32: Drug Therapy to Decrease Histamine Effects and Allergic Response

Histamine (H1)

-1st chemical mediator released in our immune system and inflammatory response -Found in mast cells and circulating in basophils Released in response to irritating stimuli (allergic reactions, cellular injury, extreme cold) -After its release, its target cells are in the blood vessels, respiratory & GI tract -stored in most body tissues but is extremely high in exposed to the environment such as eyes, nose, lungs, and GI tract -histamine will bind to a receptor site and that will stimulate them

Clinical Manifestations: Drug Reactions

-Any drug may cause reaction -Any body tissue may be involved/affected -one drug may cause multiple symptoms -reaction may be d/t dye or preservative in drug not actual drug

When histamine stimulates its receptors:

-Contraction of smooth muscles in respiratory tract (tight airway, wheezing) -Stimulation of Vagus nerve (cough & bronchoconstriction) -Increased permeability of veins & capillaries (fluid will move into sub q tissue & that will lead to edema) -Increased secretion from mucus glands (mucosal edema leading to congestion & a runny nose) -Stimulation of peripheral nerve endings (pain & itching) Dilation of capillaries in skin (flushing as blood rushes out) -Increase secretion of gastric acid -Increased heart rate and force of contraction -lots of nasty side effects -responses will vary based on what causes the reaction and what kind of reaction we have

Hypersensitivity (Allergic) Reactions

-Involves an exaggerated allergic response -Can cause tissue damage & serious illness -Caused by an abnormal immune reaction -Details of that immune reaction covered in detail in another chapter -involves a harmless antigen or irritant that usually will not cause a reaction but causes an abnormal allergic response -after we have had this reaction, our immune system remembers this antigen or irritant and it can set of this reaction & release histamine you are exposed ex. Every time you eat shrimp, your body breaks out in hives

Type III Hypersensitivity/Allergic Reaction

-Mediated/started by IgG or IgM -IgG or IgM form antigen-antibody complexes à acute inflammatory reaction in tissue -Serum sickness

Type I Hypersensitivity/Allergic Reaction

-Occurs within minutes of exposure to antigen IgE induced Mast cell activation by IgE -Usually after 2nd or later exposure -Anaphylaxis (mild to severe) -Mild: itching, rhinitis (runny nose) -Severe: respiratory distress cardiac collapse, death/life threatening, can be a very serious & fast reaction -caused by activation of mast cells by IgE. When this antigen meets IgE, histamine is released and reaction ensues. This reaction can happen so fast bc your body has already made antibodies to look for this antigen so when antigen and antibody meet there is a full blown antibody reaction -you may have had a little reaction such as itching in you mouth the 1st time you ate shrimp such as itching in your mouth. Your body will make antibodies that look for shrimp so the next time you eat it, your body will have an allergic reaction

Type II Hypersensitivity/Allergic Reaction

-Type II or cytotoxic -Mediated/caused by antibody IgG or IgM -Generates/causes direct damage to cell surface -Blood transfusion reactions -Hemolytic disease of newborns, hemolytic anemia -common reaction to certain drugs like penicillin & heparin

Type IV Hypersensitivity/Allergic Reaction

-Type IV or Delayed hypersensitivity -Cell-mediated response -Sensitized T lymphocytes react with antigen to cause inflammation. Examples: -Tuberculin test -Contact dermatitis -Graft rejection delayed reaction time -happens after exposure to antigen, a T cell reacts and cause inflammation -contact dermatitis: if you touch poison ivy, you don't get the rash until the next day bc it is a type 4 sensitivity

Second-generation H1 receptor antagonists: Nursing Considerations

2nd generation safer with older adults d/t less CNS effects Use caution in renal failure bc excretion may be a little slower

First-generation H1 receptor antagonists: Indications

Allergic reaction Motion sickness Insomnia Children may experience paradoxical/opposite effect (crazy hyper instead of sleepy

First-generation H1 receptor antagonists: Drug-Drug Interactions

Antidepressants CNS depressants

First-generation H1 receptor antagonists: Adverse Effects

CNS depression Anti cholinergic effects (dry mouth, urinary retention, constipation & 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 notcrossthe blood brain barrier

D. Do not cross the blood brain barrier Rationale: Second generation H1 antagonists like Fexofenadine do NOT enter the brain reducing the side effect of sedation. 2nd gen more selective

First-generation H1 receptor antagonists: Example

Diphenhydramine

Second-generation H1 receptor antagonists: General Info

Does not readily enter the brain from the blood Bind preferentially to peripheral rather than central H1 receptors Replacing first-generation H1 for tx of allergies (more selective & less CNS effects) Have a mild beneficial effect in chronic asthma by decreasing airway irritation

Is the following statement True or False? Allergic rhinitis is caused by type III sensitivity.

False Rationale: Allergic rhinitis is inflammation of nasal mucosa caused by a type I hypersensitivity reaction to inhaled allergens type 3 causes serum sickness

Second-generation H1 receptor antagonists: Examples

Fexofenadine Loratadine, Cetirizine (Allegra & Claritin)

Clinical Manifestations: Allergic Food Reactions

Immune response to ingestion of a protein Shellfish, fish, corn, seeds, bananas, egg, milk, soy, peanut, tree nuts Higher risk of triggering anaphylaxis Children allergic to milk, eggs, wheat, soy May outgrow their allergy No known preventative of food allergies

First-generation H1 receptor antagonists: Contraindications

Narrow angle glaucoma (d/t anticholinergic effects) BPH (d/t anticholinergic effects)

Allergic Rhinitis: Symptoms

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

First-generation H1 receptor antagonists: Action

Occupy same receptors as Histamine which prevents histamine from reaching target histamine receptor is filled by the medication and allergic reaction is blocked

First-generation H1 receptor antagonists: General Info

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 block histamine receptor site so they stop reaction cascade from histamine release

Antihistamines: Indications for Use

Relieve symptoms but do not relieve/cure hypersensitivity: -Allergic rhinitis -Anaphylaxis -Allergic conjunctivitis -Drug allergies, pseudoallergies -Blood/blood product transfusion -Dermatologic conditions, etc. (ex. Poison ivy)

Allergic Rhinitis: Seasonal (AKA hay fever)

Response to airborne pollens seasonal irritants such as pollen from trees, grass or weeds, most common in spring & fall

Allergic Rhinitis: Perennial

Response to nonseasonal allergens, chronic condition caused by: Dust mites Molds Animal dander

Second-generation H1 receptor antagonists: Indications

Seasonal allergic rhinitis Minor allergies Itching

Drug Reaction symptoms vary but may include:

Skin rash (may be full body), itching, fever, hematologic (hemolytic anemia) or hepatic reactions (liver toxicity) May occur 7-10 days after initial exposure Resolves a few days after drug DC'd

Second-generation H1 receptor antagonists: Patient Education

Take med before exposure to allergen Avoid taking with Alcohol (may increase potential for sedation) Avoid accidental OD (combo drugs) Teach proper nasal spray use if needed

First-generation H1 receptor antagonists: Patient Teaching

Take med before exposure to allergen** Tolerance to drowsiness in few days Avoid taking with Alcohol (because of extra CNS depression) Avoid accidental OD in use with combo meds

Is the following statement True or False? Four classifications of hypersensitivity reactions exist.

True Rationale: Four classifications of hypersensitivity reactions exist: type I (immediate), type II (direct damage to cell surfaces), type III (formation of antigen-antibody complexes), and type IV (delayed hypersensitivity).

Is the following statement True or False? Histamine is the first chemical mediator released during inflammatory response.

True Rationale: Histamine is the first chemical mediator released during immune and inflammatory response. It is synthesized and stored in most body tissues. mast cells and basophils release histamine

Clinical Manifestations: Contact Dermatitis

Type IV/delayed reaction from direct contact with antigen (rash happens around 24 hours after contact) Poison ivy, cosmetics, metals Affected skin Inflamed, warm, swollen, itchy Blisters may form, drain, and become infected

First-generation H1 receptor antagonists: Nursing Considerations

Use caution in older adults, may cause confusion, dizziness & increased fall risk May thicken secretions making them harder to cough or blow out

Types I, II, II

antibody molecules

Type IV

antigen-specific T cell reaction

main allergy drugs are...

antihistamines

breastfeeding has shown to prevent food allergies as as a child but

increase them as person ages

Clinical Manifestations: Allergic Rhinitis Definition

inflammation of nasal mucosa caused by type I reaction to inhaled allergens such pollen -after you inhale the antigen pollen, your body quickly sets off a histamine reaction

when mucous membranes are inflamed...

irritants like tobacco smoke, chemicals and air pollution can make symptoms even worse

Second-generation H1 receptor antagonists: Action

occupy same receptors as histamine which prevents histamine from reaching target fill receptor sites and blocks histamine reaction

Two Types of Allergic Rhinitis

seasonal and perennial

ost common food allergy in adults:

shellfish

if not treated, allergic rhinitis may cause

sleep issues, sinus infection, coughing and headaches and may put person at risk for asthma

Four types based on...

the producing mechanism/cause of the reaction

serum sickness

when excessive antigens combine with antibodies causing tissue damage and immune complexes which can cause permanent damage