Drug Therapy to Decrease Histamine Effects and Allergic Response

First-generation H1 receptor antagonists

Diphenhydramine •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 ACTION: •Occupy same receptors as Histamine which prevents histamine from reaching target USE: •Allergic reaction •Motion sickness •Insomnia •Children may experience paradoxical effect •Adverse effects: •*CNS depression •Anti cholinergic effects CONTRAINDICATIONS: •Narrow angle glaucoma •BPH NURSING CONSIDERATIONs: •Use caution in older adults, may cause confusion •May thicken secretions PATIENT EDUCATION: •Take med before exposure to allergen •Tolerance to drowsiness in few days •Avoid taking with Alcohol •Avoid accidental OD

Second-generation H1 receptor antagonists

Fexofenadine Loratadine, Cetirizine •Dose not readily enter the brain from the blood •Bind preferentially to peripheral rather than central H1 receptors •Replacing first-generation H1 •Have a mild beneficial effect in chronic asthma ACTION: •Occupy same receptors as Histamine which prevents histamine from reaching target USE: •Seasonal allergic rhinitis •Minor allergies •Itching NURSING CONSIDERATIONS •Safer in older Adults •Use caution in renal failure PATIENT TEACHING: •med before exposure to allergen •Teach proper use of nasal spray if needed •Avoid taking with Alcohol •Avoid accidental OD

Allergic Rhinitis

Inflammation of nasal mucosa caused by type I reaction to inhaled allergens Symptoms: •Nasal congestion •Itching, sneezing •Watery drainage •Itching of throat, eyes, ears common Seasonal disease (AKA, hay fever) •Response to airborne pollens Perennial disease •Response to nonseasonal allergens •Dust mites, molds •Animal dander

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

false Allergic rhinitis is inflammation of nasal mucosa caused by a type I hypersensitivity reaction to inhaled allergens

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

true •Histamine is the first chemical mediator released during immune and inflammatory response. It is synthesized and stored in most body tissues.

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

true •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).

Histamine (H1)

•1st chemical mediator released •Found in Mast cells and Basophils •Released in response to stimuli (allergic reactions, cellular injury) •After its release, its target cells are in the blood vessels, respiratory & GI tract

Drug reactions

•Any drug may cause reaction •Any body tissue may be involved •Symptoms vary but may include -Skin rash, itching, fever, hematologic or hepatic reactions •May occur 7-10 days after initial exposure •Resolves after drug DC'd

•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 blood brain barrier

•D. Do not cross the blood brain barrier •Second generation H1 antagonists like Fexofenadine do NOT enter the brain reducing the side effect of sedation.

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

Hypersensitivity reactions

•Involves an exaggerated allergic response •Can cause tissue damage & serious illness •Caused by an abnormal immune reaction •Four types based on the producing mechanism -Types I, II, III: antibody molecules -Type IV: antigen-specific T cells

Antihistamines

•Relieve symptoms but do not relieve hypersensitivity •Allergic rhinitis •Anaphylaxis •Allergic conjunctivitis •Drug allergies, pseudoallergies •Blood/blood product transfusion •Dermatologic conditions, etc.

Type 1 hypersensitivity

•Type 1 or Immediate hypersensitivity •Occurs within minutes •IgE induced Mast cell activation •Usually after 2nd or later exposure •Mild to severe •Mild: itching, rhinitis •Severe: Anaphylaxis-respiratory distress cardiac collapse, life threatening

Type II Hypersensitivity

•Type II or cytotoxic •Mediated by IgG or IgM •Generates direct damage to cell surface •Blood transfusion reactions •Hemolytic disease of newborns, hemolytic anemia

Type III Hypersensitivity

•Type III or Immune complex •Mediated by IgG or IgM •Forms antigen-antibody complexes à acute inflammatory reaction in tissue •Serum sickness

Type IV Hypersensitivity

•Type IV or Delayed hypersensitivity •Cell-mediated response •Sensitized T lymphocytes react with antigen to cause inflammation •Tuberculin test •Contact dermatitis •Graft rejection

Contact Dermatitis

•Type IV reaction from direct contact with antigen -Poison ivy, cosmetics, metals •Affected skin -Inflamed, warm, swollen, itchy -Blisters may form, drain, and become infected

the allergic response

•When histamine stimulates its receptors: -Contraction of smooth muscles in respiratory tract -Stimulation of Vagus nerve -Increased permeability of veins & capillaries -Increased secretion from mucus glands -Stimulation of peripheral nerve endings -Dilation of capillaries in skin -Increase secretion of gastric acid -Increased heart rate and force