Allergies and Allergic Reactions
N609

Allergy is an abnormal release of energy in the body.
In clinical or physiologic terms, allergy is an exaggerated immune response resulting from an antibody-antigen reaction.
This exaggerated response to an antigen is referred to as hypersensitivity.
Anergy (in contrast to allergy) is the term used to describe the unexpected failure of the immune system to respond to the challenge of a foreign substance (antigen or allergen).

Type I reactions involve the interaction between an antigen and a specific immunoglobulin (Ig) E antibody. Ex. asthma, allergic rhinitis, anaphylaxis.
Type II reactions, also known as cytotoxic reactions, occur when an antibody reacts with an antigenic component of a cell. Ex. transfusion reaction.
Type III reactions result from immune complexes that activate the complement system. Ex. systemic lupus erythematous.
Type IV reactions are also called delayed hypersensitivity reactions. These cell-mediated reactions are the result of sensitized T lymphocytes coming into contact with a specific antigen. Ex. allergic dermatitis.

A practitioner is prescribing medication for a patient who has poison ivy on his arms. What type of reaction is this patient experiencing?
A. Type I
B. Type II
C. Type III
D. Type IV

D. Type IV
Rationale: In type IV (delayed hypersensitivity), antigen-sensitized T cells release inflammatory substances after a second contact with the same antigen. (Contact dermatitis, such as poison ivy, and the tuberculin skin test [PPD] are examples of delayed hypersensitivity.)

Some cutaneous reactions, such as contact dermatitis, may appear to be allergic reactions, but they do not involve the immune system.
Irritant contact dermatitis is the most common cutaneous reaction and is often caused by skin irritants such as powders or chemicals found in gloves.

The first step in treating an allergic reaction is to remove the allergen, if possible.
This may involve removing the person from the environment causing the allergy, stopping the offending drug, or washing off the offending chemical.

Cutaneous reactions such as urticaria, pruritus, and hives are often secondary to the release of histamine, making antihistamine therapy the mainstay of treatment.

Anaphylaxis is a type I hypersensitivity reaction involving IgE-mediated release of histamine, leukotrienes, and other mediators from already sensitized mast cells and basophils.
The release of these mediators initiates a systemic chain of events that includes symptoms such as angioedema, flushing, pruritus, urticaria, nausea, vomiting, and wheezing.
The onset of the reaction is quick, generally within 1 to 30 minutes.
Anaphylactoid reactions are similar in appearance to anaphylaxis but may occur after the first injection of certain drugs and contrast media.

Immediate treatment with epinephrine is imperative. Epinephrine effectively increases the blood pressure and is an antagonist to the effects of histamine on smooth muscle and other tissues.

The primary means of preventing an allergic reaction is avoidance.
However, when this is not feasible or practical, immunotherapy is an effective means of preventing reactions, particularly anaphylactic reactions from insect bites.
This form of "desensitization" is only effective when a specific allergen can be identified. Some ragweed and pollen allergies respond well to immunotherapy, though it may take several months before immunity is conferred.

Definition: airway allergy
Causes: pollen (grass, trees, weeds), dust mites, mold spores, enzymes (in detergents), and insect body parts
Types: seasonal, perennial

Ocular pruritus (itching of the eyes)
Conjunctival inflammation (inflammation of the membrane lining the eyelids)
Irritability, lethargy, fatigue, loss of appetite
Rhinorrhea
Nasal congestion
Nasal pruritus

Initial exposure to the antigen/allergen stimulates the B lymphocytes (plasma cells) to produce an antigen-specific antibody (IgE) that binds to mast cell membranes (tissue-fixed antibody).
The person is now sensitized to that specific antigen and susceptible to allergic reactions when re-exposed to it.
On subsequent exposure, the antigen binds to the tissue-fixed IgE antibody and triggers breakdown of the mast cells (degranulation) and release of mediators (histamine, prostaglandins, leukotrienes, kinins, thromboxanes, and serotonin).

Facial appearance
Nasal smears
Skin testing
Radioallergosorbent testing
Differential diagnosis

A practitioner suspects a patient has allergic rhinitis. What would be the first step in managing this condition once diagnosis is confirmed?
A. Begin nonpharmacologic treatment
B. Begin antihistamines daily
C. Begin decongestants
D. Institute immunotherapy

A. Begin nonpharmacologic treatment
Rationale: Nonpharmacologic treatment, such as avoiding the offending organism, using air conditioners, etc., is the first line of treatment for allergic rhinitis. Next, antihistamines either alone or in combination with a nasal decongestant or intranasal corticosteroids are tried. If symptoms still persist, immunotherapy is initiated.

Alleviate the symptoms with little to no adverse effects from medications.
This is accomplished primarily through decreasing the release or inhibiting the effect of histamine release and other mediators of inflammation from mast cells.

Antihistamines
The first-generation antihistamines, such as diphenhydramine, chlorpheniramine, and brompheniramine, are the older antihistamines.
More recently, antihistamines have been developed that do not cross the blood-brain barrier to the extent exhibited by the older agents. These newer antihistamines, commonly referred to as NSAs, are considered to act peripherally and do not produce sedation or cause clinically important changes in mental status.

A practitioner is prescribing pseudoephedrine for a 7-year-old patient diagnosed with allergic rhinitis. What is the recommended dosage?
A. 60 mg q6h
B. 30 mg q6h
C. 10-20 mg q4h
D. 120 mg q12h

B. 30 mg q6h
Rationale: The recommended dosage for pseudoephedrine for children 6-12 years is 30 mg q6h (120 mg). For children 2-6 years, the dosage is 15 mg q6h (60 mg). For adults, the dosage is 60 mg q6h (240 mg); extended release is 120 mg q12h; controlled release is 240 mg q24h.

Azelastine (Astelin) and olopatadine (Patanase) intranasal antihistamines are also available to treat allergic rhinitis.

Nasal decongestants are sympathomimetic amines chemically related to norepinephrine, a major neurotransmitter of the sympathetic nervous system.
These drugs are vasoconstrictors. They offer relief from nasal congestion by constricting the blood vessels of the nasal mucosa that have been dilated by histamine and are available in either oral or topical nasal formulations.
The results are a shrinking of swollen nasal passages and more air movement to make breathing easier.

Intranasal application (sprays or drops) of sympathomimetic amines provides a prompt and dramatic decrease of nasal congestion.
A rebound phenomenon (rhinitis medicamentosa), however, often follows topical application of these drugs.

Nasal-inhaled corticosteroids are the most effective forms of therapy for allergic rhinitis.
They help to relieve congestion and rhinorrhea by limiting the late-phase response and reducing inflammation.

Pediatric
Geriatric
Women

Patient education
Drug information
Patient-oriented information sources
Complementary and alternative medications

The signs and symptoms of allergic conjunctivitis result from the same allergens that cause allergic rhinitis.
Mast cells are abundant in the eyelid and conjunctiva but are infrequently found in the eye.
This limits allergic ocular inflammation to the lining of the eyelid and the ocular surface (the conjunctiva).

All people come in contact with the same antigens, yet not all people display allergic symptoms.
Allergy symptoms appear when the immune response is exaggerated or inappropriate, causing inflammation and tissue damage.
The first step in treating an allergic reaction is to remove the allergen, if possible. Most allergic reactions clear up within a few days of removing the cause.
Symptomatic cutaneous reactions should be treated with antihistamines and decongestants.