Treatment may vary depending on the type of allergic reaction. Some general observations are made below, but refer to articles on the specific topics for more details about treatment (eg, Anaphylaxis; Rhinitis, Allergic; Allergic and Environmental Asthma; Urticaria).
Assessment of the reaction is described as follows:
Withdraw the offending agent if applicable (eg, stop drug infusion).
Check the airway and secure if needed. Patients with respiratory compromise may need to be intubated. If laryngeal edema causes oral intubation to be difficult, a tracheostomy must be performed.
Assess the level of consciousness and vital signs.
Treatment is as follows:
Administer epinephrine immediately (see Medication). This is the most important medication and the only medication that has been shown to decrease mortality due to anaphylaxis.
Start intravenous fluids; these should be administered rapidly and as blood pressure and overall fluid status warrant.
Consider other vasopressors (eg, dopamine) if hypotension does not respond to the above measures. Norepinephrine may be used if dopamine is not effective. Importantly, isoproterenol should not be used because it is a peripheral vasodilator. Patients with beta-adrenergic blockade may be particularly difficult to treat. They have both chronotropic and inotropic cardiac suppression and may not respond to the above treatments. Glucagon has positive inotropic and chronotropic effects and is the drug of choice in these cases. Atropine can also be used but will only be effective in treating bradycardia.
H1- and H2-receptor blockers can be helpful in alleviating hypotension, pruritus, urticaria, rhinorrhea, and other symptoms. Cimetidine, when combined with any of several H1 antihistamines, has been demonstrated to block histamine-induced hypotension. Other H2 blockers have not been studied in this context.
Use albuterol nebulizers if needed.
Administer a corticosteroid, which is believed to help prevent or control the late-phase reaction.
Transfer the patient to the hospital for further observation and care.
Late phase reactions can occur 4-6 hours after the initial reaction and can be as severe as or worse than the original reaction. In some cases, late phase reactions can occur up to 72 hours later. Education of the patient and observation is, therefore, important.
Prevention is as follows:
Avoid the triggering allergen as much as possible.
Patients should be given a prescription for at least 2 autoinjectable epinephrine doses and instructed in their proper use. Importantly, patients must carry them at all times.
Patients must wear a Medic Alert type of bracelet to alert emergency responders to the possibility of anaphylaxis.
Patients should be taught what measures to take in case of a future anaphylactic reaction, ie, immediately administer epinephrine and take the antihistamine, call emergency services (eg, 911), or go to the nearest emergency department (even if feeling better after the epinephrine).
Specific allergen immunotherapy is highly effective in preventing anaphylaxis from hymenoptera stings and should always be considered for patients who have experienced a systemic reaction after an insect sting.
Avoid the offending allergen, if possible.
Oral H1-receptor blockers are helpful for controlling itchiness, rhinorrhea, and lacrimation but most have little effect on nasal congestion.
Administer an intranasal glucocorticosteroid to control nasal symptoms, including nasal congestion. These medications need to be used regularly to be effective, and patients may need to use them for a week or more before maximum effect is seen.
Other topical nasal agents include azelastine and olopatadine (H1-receptor blockers).
Nasal azelastine and olopatadine have the advantage of treating rhinorrhea, nasal itchiness, sneezing, and also congestion. Azelastine has been shown to be helpful in treating both allergic and nonallergic vasomotor rhinitis. Nasal antihistamines have a rapid onset of action and can be used on an as-needed basis. Topical nasal decongestants can provide immediate relief of nasal congestion and can be used temporarily and as needed. Patients should be cautioned not to use them for more than a few days, however, as they can cause rebound congestion (rhinitis medicamentosa).
Topical decongestants, mast cell stabilizers, or antihistamines can be used for ocular symptoms; artificial tears or sterile saline might be helpful in mild cases, and this product can be refrigerated for an extra cooling effect. Cold compresses can also be used.
Again, use of topical decongestants should be limited to a few days, as longer use can result in rebound vasodilation.
Antigen-injection immunotherapy is very effective in treating inhalant allergies and can be considered in patients whose symptoms do not respond well to medications or in patients who cannot avoid the allergen in question (eg, cat owner allergic to cats). The mechanism of action of immunotherapy is not yet fully elucidated. Immunotherapy causes antigen-specific immunoglobulin G4 to be formed and lowers antigen-specific IgE over time. It is thought to dampen the TH2 response. Some feel it also tips the balance of TH2 and TH1 towards a TH1 phenotype. Importantly, regulatory T cells play an important role through the production suppressive cytokines IL-10 and TGF-β. [35, 8]
An alternative to antigen-injection immunotherapy, aka, subcutaneous immunotherapy (SCIT), is sublingual/swallow immunotherapy (SLIT), which is used in Europe and has been approved by the FDA in the United States. The SLIT formulations approved for use in the US are Ragwitek, Grastek, and Oralair. The first dose of each tablet needs to be supervised by an allergist. Each patient should be prescribed and taught how and when to use auto-injectable epinephrine.
Grastek (manufactured by Merck) is timothy grass allergen extract approved for patients 5-65 years old who are allergic to grass pollen. One tablet is taken sublingually daily for 12 weeks prior to grass pollen season and throughout the season as well. 
Ragwitek (manufactured by Merck) is short ragweed allergen extract approved for patients 18-65 years old who are allergic to short ragweed. One tablet is taken sublingually daily for 12 weeks prior to short ragweed season and throughout the season. 
Oralair (manufactured by Greer) is a mixture of five grass allergen extracts. It is approved for patients 10-65 years old who has grass pollen allergy. One tablet is taken sublingually for four months prior to grass pollen season and throughout the season. 
Avoid the offending allergen, if possible.
A key factor in controlling allergic asthma is controlling allergic rhinitis symptoms.
Therapy depends on the severity of disease as well as age of patient. In 2007, the National Asthma Education and Prevention Program (NAEPP) Expert Panel from the National Heart, Lung, and Blood Institute (NHLBI) released guidelines on the diagnosis and management of asthma. These guidelines use a stepwise treatment approach based on age and severity of the asthmatic treated. 
All asthmatics are classified as intermittent, mild persistent, moderate persistent or severe persistent based on risk and impairment (see History for asthma for details).
Age of the patient, along with symptoms, will also help guide treatment options. Step 1 treatment is for intermittent asthmatics while Steps 2-6 listed below are the preferred daily medications for persistent asthmatics from the guidelines.  Alternative treatment options are listed in the guidelines. 
Table. (Open Table in a new window)
|Age||Step 1||Step 2||Step 3||Step 4||Step 5||Step 6|
|0-4 years||SABA PRN||Low-dose ICS||Medium-dose ICS||Medium-dose ICS plus LABA or montelukast||High-dose ICS plus LABA or montelukast||High-dose ICS plus LABA or montelukast and oral corticosteroids|
|5-11 years||SABA PRN||Low-dose ICS||Low-dose ICS plus LABA or LTRA or theophylline||Medium-dose ICS plus LABA||High-dose ICS plus LABA||High-dose ICS plus LABA plus oral corticosteroids|
|12 years or older||SABA PRN||Low-dose ICS||Low-dose ICS plus LABA or medium-dose ICS||Medium-dose ICS plus LABA||High-dose ICS plus LABA||High-dose ICS plus LABA plus oral corticosteroids|
Symptoms and SABA use should be reassessed after starting treatment. If patients are well-controlled for 3 months, step down therapy may be employed. Conversely, if a patient’s symptoms are not well-controlled, step up therapy is warranted.
All patients with asthma should have an albuterol metered-dose inhaler (MDI) (or nebulizers for young children) to use as needed for acute symptoms.
Patients with exercise-induced bronchospasm (EIB) should receive short-acting beta2-agonist treatment 15-20 minutes prior to exercise.
Systemic corticosteroid bursts may need to be used for exacerbations of severe cases.
Patients with allergic asthma may respond well to specific allergen immunotherapy. This is recommended from Steps 2-4 in patients 5 years or older. 
In patients 12 years or older refractory to the usual medications (Steps 5 and 6) who have antigen-specific IgE to perennial environmental aeroallergens, may benefit from therapy with omalizumab (Xolair), a humanized monoclonal antibody that prevents binding of IgE to high-affinity IgE receptors on mast cells and basophils. [39, 40, 41, 31]
Avoid the offending allergen if known.
A second-generation H1-receptor blocker should be added for monotherapy (i.e., cetirizine 10 mg daily). 
If symptoms are not controlled with this alone, the dose of the second generation H1 antagonist can be increased up to four times the recommended dose (i.e., cetirizine 20 mg BID). Alternatively, another second generation H1 antagonist (i.e., fexofenadine) or a first generation H1 antagonist (i.e., hydroxyzine at bedtime) can be added. Other possible treatments with H2 antagonists or leukotriene modifiers can also be added. 
If symptoms continue to occur, increasing the first generation H1 antagonist may be helpful. 
Omalizumab has been found to be useful in patients with chronic urticaria refractory to high dose treatment with H1 antihistamines (ref60) and is now FDA approved for refractory chronic urticaria. In addition, other biologics such as cyclosporine. 
Avoid the offending allergen if possible, and properly hydrate and care for the skin.
Consultation with an allergist, pulmonologist, and/or critical care medicine specialist may be necessary for protracted anaphylactic shock or severe asthma exacerbations.
Consult an allergist or immunologist for the following conditions:
Allergic rhinitis not easily controlled with medications
Nonallergic, vasomotor rhinopathy
Asthma: Of patients with asthma, at least 50% of adults have allergies as factors causing or contributing to their asthmatic inflammation. More than 90% of children with asthma are allergic.
Allergy evaluation prior to the initiation of Xolair
Chronic urticaria or angioedema (>6 weeks), or severe intermittent urticaria or angioedema, even if individual attacks last < 6 weeks
History of anaphylaxis from insect bite or sting
History of anaphylaxis with unknown cause
Possible drug desensitization (if known allergy to drug for which no good alternatives are available)
Atopic dermatitis, moderate to severe
Sinusitis before proceeding to surgery; nasal polyposis
Food allergy or idiosyncrasy
Persistent or bothersome conjunctivitis
Eosinophilic esophagitis or gastritis
Suspicion of congenital or acquired immune abnormalities
Diagnosis and treatment of acquired immunoglobulin deficiencies
Patients should avoid foods to which they are allergic.
Certain food proteins can cross-react with other proteins (eg, latex with avocado, banana, kiwi, chestnut, pineapple, passion fruit, apricot, and grape; ragweed with watermelon, cantaloupe, and honeydew melon; tree fruits with birch pollen).
Patients must be counseled about these possible cross-reactivities and should avoid the food if it causes symptoms.
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