There are various allergy medications used to reduce the immunological response seen in allergies. The most common and well known of these allergy medicines are antihistamines, with corticosteroids being used with increasing frequency to prevent exacerbations in common allergic diseases.
However, antihistamines and corticosteroids are not the only types of medications to treat allergic reactions. Other allergy medicines include mast cell stabilizers, leukotriene pathway inhibitors and anti-IgE antibodies. Adrenaline is used in severe allergic reactions and anaphylaxis.
Other Allergy Medications
Mast Cell Stabilizers
Mast cell stabilizers are drugs that prevent degranulation and release of histamine from the mast cells. These drugs are useful in preventing allergic disorders, especially those affecting the airways (allergic rhinitis, allergic asthma) or eyes (allergic conjunctivitis). Mast cell stabilizers inhibit the release of mediators of immune reactions from mast cells. It also suppress the activation of cells of immune reactions by these chemical mediators.
Cromolyn sodium (disodium cromoglycate) and nedocromil sodium are two types of mast cell stabilizers. Cromolyn sodium is available for inhalational use in bronchial asthma, as a nasal spray for allergic rhinitis and as tablets for gastrointestinal allergies. Nedocromil sodium is another type of mast cell stabilizer available for bronchial asthma but is not approved for use in children below 12 years of age.
- Allergic asthma
- Exercise-induced asthma
- Allergic rhinitis
- Allergic conjunctivitis
- Gastrointestinal allergies like systemic mastocytosis
Side Effects :
Cromolyn and nedocromil are well tolerated and have limited adverse effects due to poor systemic absorption. Adverse effects are mild and rare. These include throat irritation, bronchospasm, cough, laryngeal edema, angioedema, headache, rash, gastroenteritis and nausea. Some of these adverse effects can be prevented by pretreatment with a beta 2-adrenoceptor agonist like salbutamol before treatment with cromolyn or nedocromil. Very rarely anaphylaxis is also seen with the use of these drugs.
Leukotriene Pathway Inhibitors
Leukotriene pathway inhibitors are drugs that inhibit the synthesis of leukotrienes or block the actions of leukotrienes. Leukotrienes like LTB4, LTC4, LTD4 and LTE4 are involved in allergic inflammatory reactions like mucosal edema, mucus secretion, increased bronchial reactivity to histamine and bronchoconstriction. Leukotrienes are synthesized from arachidonic acid by an enzyme called 5-lipoxygenase. Inhibition of the enzyme 5-lipoxygenase blocks the synthesis of leukotrienes.
The currently available leukotriene pathway inhibitors are 5-lipoxygenase inhibitors like zileuton and leukotriene receptor (LTD4) antagonists like pranlukast, zafirlukast and montelukast. Some of these leukotrine pathway inhibitors are no longer available in certain countries.
Leukotriene pathway inhibitors are used for the prevention of bronchial asthma and allergic rhinitis. It reduces the frequency of episodes of allergic rhinitis and bronchial asthma. Some patients respond particularly well, while others fail to make any significant improvement. It has also been found to be of benefit in aspirin-induced asthma.
Side Effects :
Zileuton is believed to cause liver toxicity in about 5% of the patients taking it within 2 months of initiation of treatment. It has therefore been discontinued in some countries. Leukotriene receptor blockers are well tolerated with minimal side effects.
Anti-IgE antibodies act against IgE antibodies thereby reducing allergic responses due to histamine release from mast cells. Anti-IgE antibodies are a new approach to treating allergic diseases like allergic bronchial asthma. It targets the part of IgE antibody that binds to mast cells thereby preventing binding of IgE antibody to the mast cells and basophils.
This prevents activation of the mast cells and suppresses the IgE-mediated release of histamine and leukotrienes. Repeated anti-IgE antibody administration significantly lowers IgE levels in plasma to negligible levels in asthma patients. This minimizes the immune responses to allergens at an early stage and reduces the frequency and severity of asthma attacks.
Omalizumab is an anti-IgE monoclonal antibody which is approved for use in bronchial asthma. It is a humanized recombinant murine (mouse) antibody. Omalizumab is used for moderate to severe allergic asthma which is not responding to inhaled corticosteroids in adults and adolescents. It is of no use in acute attacks, but of value in reducing asthma attacks. Regular omalizumab use reduces corticosteroids necessity in bronchial asthma and may also improve the symptoms of allergic rhinitis and food allergy but is not approved for these indications.
Side Effects :
Anaphylaxis is the most serious adverse drug reaction seen with omalizumab. It is characterized by bronchoconstriction, urticaria, low blood pressure and/or laryngeal edema. Irritation at the injection site like redness and a stinging sensation are the most frequent adverse drug reactions.
Adrenaline is a hormone secreted from the medulla of the adrenal gland. The actions of adrenaline are exerted through adrenergic receptors (alpha and beta), to which it binds and activates. In allergic states, it is mainly used for anaphylaxis and very severe acute exacerbations in chronic allergic diseases like asthma.
Adrenaline is a potent cardiac stimulant and increases the heart rate and systolic blood pressure. It also dilates the bronchial smooth muscles and improves the breathing in asthmatic patients.
Anaphylactic shock results from the IgE-mediated allergic reaction which is associated with release of large quantities of histamine from mast cells. The main consequences of histamine release like bronchospasm, angioedema and severe drop in blood pressure are reversed by adrenaline. These symptoms of anaphylaxis respond immediately to the intramuscular injection of adrenaline. Sometimes the intravenous (IV) injection of adrenaline may be required if the cardiac function is severely affected by the shock. Adrenaline improves both cardiac and respiratory symptoms of anaphylaxis.
Patients known for repeated anaphylactic reactions like severe food allergy or insect bite reactions are advised to carry adrenaline for self administration in an auto-injector. Adrenaline can suddenly increase the heart rate and cardiac workload and should be carefully administered in patients with ischemic heart disease or cardiac arrhythmia.