Type I Hypersensitivity Reaction

Type I hypersensitivity reaction is an abnormal immune response triggered by exposure to specific antigens known as allergens. In this type of hypersensitivity reaction, the presentation of the antigen to the T-helper cells (Th cells) initiates a cascade of immunologic events leading to the production of antigen-specific IgE antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins. Reexposure to the antigen promotes degranulation of the IgE-bound mast cells and basophils, releasing chemical mediators that cause various allergy symptoms. Manifestations can be local, depending on the route of entry of the antigen. In severe cases, systemic reaction leads to anaphylactic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock. To determine allergic etiology, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin testing as well as in vitro tests are available. Management includes avoidance of triggers to reduce exacerbation. Common treatment options are antihistamines Antihistamines Antihistamines are drugs that target histamine receptors, particularly H1 and H2 receptors. H1 antagonists are competitive and reversible inhibitors of H1 receptors. First-generation antihistamines cross the blood-brain barrier and can cause sedation. Antihistamines and glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids to control the inflammatory response. Anaphylaxis, however, is a medical emergency that requires immediate airway access with administration of epinephrine and fluid resuscitation.

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Overview

  • Immune system
    • An integral system of cells and their products that recognizes, attacks, and destroys potentially harmful entities to the health of an individual
    • Provides normal protective immune response against pathogens
  •  Hypersensitivity reaction
    • A “hyper” or exaggerated immune response to what should be seen as harmless environmental antigens
    • Types I, II, and III are immediate reactions occurring within 24 hours.
    • Type IV reaction develops over several days.
  • Type I hypersensitivity reaction (atopy/type I immediate hypersensitivity reaction): involves immunoglobulin E (IgE)-mediated mast cell and basophil degranulation on reexposure to an antigen
  • Allergy: an abnormal adaptive immune response that may or may not involve antigen-specific IgE

Epidemiology and Etiology

Epidemiology

  • Lifetime prevalence: 15% worldwide
  • In the United States: 
    • Allergies are the 6th-leading cause of chronic illness.
    • Asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma, a form of airway hyperresponsiveness, accounts for over 500,000 hospitalizations each year.
  • Allergic diseases have increased over the past half-century, partly from lifestyle changes (improved hygiene → reduced exposure to allergens early in life) and pollution.

Etiology

  • Genetic predisposition:
    • No single dominant gene for allergy
    • Certain genes involved in the specific immune response (FcεR1 [high-affinity IgE receptor], IL-4 [interleukin 4], and other cytokines; CD14 [cluster of differentiation 14], HLA-DR [human leukocyte antigen-DR], Th1/Th2 [T-helper 1 and 2 cells] differentiation) contribute to the development of allergies.
  • Environment:
    • Allergen exposure
    • Increased air pollution
    • Bacterial and viral infection
    • Lifestyle: nutrition, hygiene, pet ownership

Pathophysiology

Sensitization stage

  • Asymptomatic; 1st antigen exposure
  • Allergen is recognized by antigen-presenting cells presented to naive T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells differentiate into Th2 cells
  • Th2 cells release interleukins Interleukins Interleukins are a type of cytokines (signaling proteins) that communicate messages between different parts of the immune system. The majority of interleukins are synthesized by helper CD4 T lymphocytes along with other cells such as monocytes, macrophages, and endothelial cells. Interleukins (IL-4, IL-5IL-13) → switches B cells B cells B lymphocytes, also known as B cells, are important components of the adaptive immune system. In the bone marrow, the hematopoietic stem cells go through a series of steps to become mature naive B cells. The cells migrate to secondary lymphoid organs for activation and further maturation. B Cells to increase IgE antibody production → IgE antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins bind to mast cells and basophils (via FcεRI receptors)

Reaction or effector stage

  • Mast cells and basophils are now bound with antigen-specific IgE antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins ready to respond on antigen re-exposure. 
  • Early-phase reaction:
    • Occurs within minutes
    • May be a local or systemic reaction 
    • IgE-bound mast cell and basophil degranulation releasing mediators cause symptoms
      • Histamine: vasodilation, bronchial smooth muscle contraction, increased mucus secretion, increased vessel permeability
      • Prostaglandin: pulmonary smooth muscle contraction, platelet aggregation
      • Platelet-activating factor: platelet aggregation, vasodilation
      • Leukotrienes: bronchial smooth muscle contraction, increased vessel permeability, mucus production  
  • Late-phase reaction:
    •  Occurs 412 hours later, peaking at 69 hours
    • Eosinophils (predominant) and other leukocytes migrate to allergen-contaminated tissue

Causes

  • Drugs (most commonly) (e.g., penicillin, cephalosporins Cephalosporins Cephalosporins are a group of bactericidal beta-lactam antibiotics (similar to penicillins) that exert their effects by preventing bacteria from producing their cell walls, ultimately leading to cell death. Cephalosporins are categorized by generation and all drug names begin with "cef-" or "ceph-." Cephalosporins,  muscle relaxants, anesthetics)
    • Medications cause the most allergy-related deaths.
  • Food (e.g., nuts, shellfish, eggs, soy, wheat, cow’s milk)
  • Insect venom (e.g., bee and wasp venom)
  • Environmental allergens (e.g., dust mites, animal dander, pollen, grass, latex)
Type i anaphylactic hypersensitivity

Pathophysiology of type 1 hypersensitivity:
1. Antigen-presenting cells (APC) recognize the allergen and presents to naive T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells
2. T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells differentiate into Th2 which release the interleukins Interleukins Interleukins are a type of cytokines (signaling proteins) that communicate messages between different parts of the immune system. The majority of interleukins are synthesized by helper CD4 T lymphocytes along with other cells such as monocytes, macrophages, and endothelial cells. Interleukins.
3. Interleukins stimulate the B cells B cells B lymphocytes, also known as B cells, are important components of the adaptive immune system. In the bone marrow, the hematopoietic stem cells go through a series of steps to become mature naive B cells. The cells migrate to secondary lymphoid organs for activation and further maturation. B Cells to produce IgE.
4. Antigen-specific IgE binds to mast cells and basophils.
5. Subsequent exposure to the same antigen leads to degranulation and release of mediators.

TCR: T cell receptor

Image by Lecturio.
Mast cells in allergy

Mast cells are involved in allergy. Allergies such as pollen allergy are related to the antibody known as IgE. Like other antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins, each IgE antibody is specific; one acts against oak pollen, another against ragweed.

Image by Lecturio.

Types of hypersensitivity

Table: Comparison of type I hypersensitivity to other types of hypersensitivity
Type I Type II Type III Type IV
IgE-mediated hypersensitivity IgG-mediated cytotoxic hypersensitivity Immune complex-mediated hypersensitivity Cell-mediated hypersensitivity
IgE is bound to mast cells via its fragment crystallizable (Fc) portion. When an allergen binds to these antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins, crosslinking of IgE induces degranulation. Cells are destroyed by bound antibody, either by activation of complement or by a cytotoxic T cell with an Fc receptor for the antibody (antibody-dependent cellular cytotoxicity). Antigen-antibody complexes are deposited in tissues, causing activation of complement, which attracts neutrophils to the site. Th1 cells secrete cytokines, which activate macrophages and cytotoxic T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells and can cause macrophage accumulation at the site.
Causes localized and systemic anaphylaxis; seasonal allergies including hay fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever; food allergies, such as those to shellfish and peanuts; hives Hives Urticaria is raised, well-circumscribed areas (wheals) of edema (swelling) and erythema (redness) involving the dermis and epidermis with associated pruritus (itch). Urticaria is not a single disease but rather is a reaction pattern representing cutaneous mast cell degranulation. Urticaria (Hives); and eczema Eczema Atopic dermatitis, also known as eczema, is a chronic, relapsing, pruritic, inflammatory skin disease that occurs more frequently in children, although adults can also be affected. The condition is often associated with elevated serum levels of IgE and a personal or family history of atopy. Skin dryness, erythema, oozing, crusting, and lichenification are present. Atopic Dermatitis (Eczema). Red blood cells are destroyed by complement and antibody during a transfusion of mismatched type or during erythroblastosis fetalis. The most common forms of immune complex disease include glomerulonephritis, rheumatoid arthritis Rheumatoid arthritis Rheumatoid arthritis (RA) is a symmetric, inflammatory polyarthritis and chronic, progressive, autoimmune disorder. Presentation occurs most commonly in middle-aged women with joint swelling, pain, and morning stiffness (often in the hands). Rheumatoid Arthritis, and systemic lupus erythematosus Systemic lupus erythematosus Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. Systemic Lupus Erythematosus. The most common forms are contact dermatitis, tuberculin reaction, diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus type I, multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis, and rheumatoid arthritis Rheumatoid arthritis Rheumatoid arthritis (RA) is a symmetric, inflammatory polyarthritis and chronic, progressive, autoimmune disorder. Presentation occurs most commonly in middle-aged women with joint swelling, pain, and morning stiffness (often in the hands). Rheumatoid Arthritis.
Source: Schatz, Phil. Diseases Associated with Depressed or Overactive Immune Responses. Anatomy and Physiology. Retrieved August 21, 2020, from https://philschatz.com/anatomy-book/contents/m46566.html

Clinical Features

Localized allergic reaction

  • Rashes Rashes Rashes are a group of diseases that cause abnormal coloration and texture to the skin. The etiologies are numerous but can include irritation, allergens, infections, or inflammatory conditions. Rashes that present in only 1 area of the body are called localized rashes. Generalized rashes occur diffusely throughout the body. Generalized and Localized Rashes or blisters in the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, pruritus ( hives Hives Urticaria is raised, well-circumscribed areas (wheals) of edema (swelling) and erythema (redness) involving the dermis and epidermis with associated pruritus (itch). Urticaria is not a single disease but rather is a reaction pattern representing cutaneous mast cell degranulation. Urticaria (Hives), atopic dermatitis Atopic Dermatitis Atopic dermatitis, also known as eczema, is a chronic, relapsing, pruritic, inflammatory skin disease that occurs more frequently in children, although adults can also be affected. The condition is often associated with elevated serum levels of IgE and a personal or family history of atopy. Skin dryness, erythema, oozing, crusting, and lichenification are present. Atopic Dermatitis (Eczema), eczema Eczema Atopic dermatitis, also known as eczema, is a chronic, relapsing, pruritic, inflammatory skin disease that occurs more frequently in children, although adults can also be affected. The condition is often associated with elevated serum levels of IgE and a personal or family history of atopy. Skin dryness, erythema, oozing, crusting, and lichenification are present. Atopic Dermatitis (Eczema))
  • Increased eye and nasal secretions, itching, sneezing (allergic rhinitis Rhinitis Rhinitis refers to inflammation of the nasal mucosa. The condition is classified into allergic, nonallergic, and infectious rhinitis. Allergic rhinitis is due to a type I hypersensitivity reaction. Non-allergic rhinitis is due to increased blood flow to the nasal mucosa. Infectious rhinitis is caused by an upper respiratory tract infection. Rhinitis/hay fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, allergic conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis)
  • Oropharyngeal mucosal edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema (food allergies)
  • Bronchospasm,  wheezing Wheezing Wheezing is an abnormal breath sound characterized by a whistling noise that can be relatively high-pitched and shrill (more common) or coarse. Wheezing is produced by the movement of air through narrowed or compressed small (intrathoracic) airways. Wheezing (bronchial asthma)
  • Gastrointestinal abnormalities such as abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, vomiting (food allergies)

Systemic reaction/anaphylaxis

  • Anaphylaxis is a severe, life-threatening systemic hypersensitivity reaction occurring within minutes of exposure to an allergen.
  • A medical emergency: fatal without immediate treatment!
  • Rapid in onset but the course can be biphasic (symptoms seem to resolve then return 13 hours later with the same severity)
  • Large quantities of inflammatory mediators released → rapid systemic vasodilation and vascular permeability → hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension and extensive tissue edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema → fluid in the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs and constriction of airways → shortness of breath and lethal suffocation → cardiovascular collapse and loss of consciousness
  • Treatment: immediate administration of epinephrine to reverse bronchoconstriction and vasodilation
Anaphylactic symptoms Effects of histamine
Rhinitis, conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis Peripheral vasodilation, increased vascular permeability, increased mucus secretion
Erythema Accumulation of blood in the capillary bed from vasodilation
Pulmonary edema Pulmonary edema Pulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure. Pulmonary Edema, angioedema Angioedema Angioedema is a localized, self-limited (but potentially life-threatening), nonpitting, asymmetrical edema occurring in the deep layers of the skin and mucosal tissue. The common underlying pathophysiology involves inflammatory mediators triggering significant vasodilation and increased capillary permeability. Angioedema, hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension Fluid shift into the stroma from increased vessel permeability, vasodilation
Pruritus, urticaria Urticaria Urticaria is raised, well-circumscribed areas (wheals) of edema (swelling) and erythema (redness) involving the dermis and epidermis with associated pruritus (itch). Urticaria is not a single disease but rather is a reaction pattern representing cutaneous mast cell degranulation. Urticaria (Hives), or hives Hives Urticaria is raised, well-circumscribed areas (wheals) of edema (swelling) and erythema (redness) involving the dermis and epidermis with associated pruritus (itch). Urticaria is not a single disease but rather is a reaction pattern representing cutaneous mast cell degranulation. Urticaria (Hives) Fluid extravasation into dermis; increase trigger of skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin sensory nerves (itch)
Bronchospasm, bronchoconstriction Bronchial smooth muscle contraction, increased mucus secretion

Diagnosis

Skin testing

  • Advantages:
    • Results available within 1520 minutes
    • Less costly
    • Patients can see the reactions, which helps them understand their allergies.
  • Contraindications:
    • Recent anaphylactic event 
    • Medications that may interfere with testing (e.g., H1 and H2 blockers, tricyclic antidepressants Tricyclic antidepressants Tricyclic antidepressants (TCAs) are a class of medications used in the management of mood disorders, primarily depression. These agents, named after their 3-ring chemical structure, act via reuptake inhibition of neurotransmitters (particularly norepinephrine and serotonin) in the brain. Tricyclic Antidepressants, prednisone) or treatment of anaphylaxis (e.g., beta-blockers) 
    • Individuals with high risk of anaphylaxis (history of immediate anaphylaxis, uncontrolled asthma, significant cardiovascular disease, frail elderly, pregnant)
  • Test methods:
    • Skin prick test (positive test is a wheal ≥ associated histamine control or > 3 mm)
    • Scratch test (rarely used)
    • Intradermal method: injection of allergen into skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin

In vitro testing

  • Advantages:
    • Does not pose a risk of allergic reaction, so suitable for high-risk individuals 
    • Not affected by patient medications
    • Not reliant on skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin condition
  • Disadvantages:
    • Expensive
    • In case of total IgE level, low or normal levels do not exclude allergy status; inciting allergen is also not specified.
  • Tests:
    • Immunoassays for allergen-specific IgE: available for food, insect venom, environmental allergen, latex, drugs
    • Total IgE level: Patients with allergic conditions often have higher levels, but the result does not indicate to which specific allergen.

Management

Localized reaction

  • Avoid triggering allergen
  • Patients need to wear a MedicAlert bracelet that notes the possibility of anaphylaxis.
  • Therapeutic options:
    • H1 blockers/ antihistamines Antihistamines Antihistamines are drugs that target histamine receptors, particularly H1 and H2 receptors. H1 antagonists are competitive and reversible inhibitors of H1 receptors. First-generation antihistamines cross the blood-brain barrier and can cause sedation. Antihistamines 
    • Inhaled bronchodilators (albuterol) and inhaled corticosteroids for asthma
    • Intranasal glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids or intranasal mast cell stabilizer for allergic rhinitis Rhinitis Rhinitis refers to inflammation of the nasal mucosa. The condition is classified into allergic, nonallergic, and infectious rhinitis. Allergic rhinitis is due to a type I hypersensitivity reaction. Non-allergic rhinitis is due to increased blood flow to the nasal mucosa. Infectious rhinitis is caused by an upper respiratory tract infection. Rhinitis
    • Vasoconstrictor/antihistamine ophthalmic drops for allergic conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis (for short-term or episodic use)
    • Oral glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids for systemic symptoms of an allergic reaction/asthma (for short-term use)
    • Leukotriene receptor antagonist (montelukast) for asthma and allergic rhinitis Rhinitis Rhinitis refers to inflammation of the nasal mucosa. The condition is classified into allergic, nonallergic, and infectious rhinitis. Allergic rhinitis is due to a type I hypersensitivity reaction. Non-allergic rhinitis is due to increased blood flow to the nasal mucosa. Infectious rhinitis is caused by an upper respiratory tract infection. Rhinitis
    • Anti-IgE immunotherapy (omalizumab) for severe asthma
  • Allergy immunotherapy (AIT)
    • Desensitization or hypo-sensitization
    • Subcutaneous or sublingual delivery
    • Alters abnormal immune response
    • Highly effective for allergic rhinitis Rhinitis Rhinitis refers to inflammation of the nasal mucosa. The condition is classified into allergic, nonallergic, and infectious rhinitis. Allergic rhinitis is due to a type I hypersensitivity reaction. Non-allergic rhinitis is due to increased blood flow to the nasal mucosa. Infectious rhinitis is caused by an upper respiratory tract infection. Rhinitis/ conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis and allergic asthma

Anaphylaxis

  • Epinephrine 0.30.5 mg intramuscularly
    • Dose can be repeated
    • Decreases mortality rates significantly!
  • Immediate intubation for impending airway obstruction Airway obstruction Airway obstruction is a partial or complete blockage of the airways that impedes airflow. An airway obstruction can be classified as upper, central, or lower depending on location. Lower airway obstruction (LAO) is usually a manifestation of chronic disease, such as asthma or chronic obstructive pulmonary disease (COPD). Airway Obstruction
  • If not intubated: oxygen support via facemask up to 10 L/min 
  • Intravenous fluids Intravenous Fluids Intravenous fluids (IVFs) are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids
  • Albuterol inhalation for bronchospasm
  • Refractory symptoms:
    • Can add an inotropic agent (dopamine, norepinephrine) 
    • Atropine for any bradycardic episodes
    • Glucagon for patients on beta-blockers who may not respond to epinephrine
  • Adjunctive treatments:
    • H1- and H2-receptor blockers 
      • Histamine antagonists
      • H2-receptor blockers (decrease stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach acid production) potentiate effect of H1-receptor blockers
    • Corticosteroid infusion

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