Common drugs used for allergy
Antihistamines used to treat allergy symptoms fall into two broad categories: sedating and non-sedating. The first category includes the older antihistamines. These allergy drugs relieve allergy symptoms but cause drowsiness and other side effects, including dry mouth. Newer antihistamines are said to be non-sedating, although some users may experience drowsiness even from these. All antihistamines work in the same way: by competing with histamine to prevent or reduce the characteristic signs and symptoms of an allergic reaction: swelling, tearing, itching, and increase in bronchial and other secretions.
Corticosteroids: These come as nasal sprays, topical creams and ointments, tablets, injectables and eye preparations. They are anti-inflammatory medicines that stop the allergic reaction. In addition to other helpful actions, they decrease the number of mast cells in the nose and reduce mucus secretion and nasal swelling. The combination of antihistamines and nasal steroids is a very effective way to control the symptoms of allergic rhinitis, especially in moderate or severe one. However, once the patient has stopped using the drug, the symptom may come back..
Mast cell stabilizers: These can help prevent allergic reactions from happening when taken regularly. During an allergic reaction, mast cells release histamine and other substances. Mast cell stabilizers, such as cromolyn sodium, keep these cells intact. It has few side effects when used as directed and significantly helps some people manage their allergies.
Leukotriene inhibitors: Other substances released during an allergic reaction are leukotrienes, which can aggravate allergic conditions and asthma. Some drugs target leukotriene receptors to reduce allergic symptoms.
Nasal anticholinergics: A runny nose is a common complaint among those with allergic rhinitis. Anticholinergic nasal sprays reduce discharge from the nose, but though they do not relieve a stuffy nose.
Decongestants: These relieve a stuffy nose by constricting blood vessels, which limits the amount of secretions coming from the inner lining of the nose. They are available as nasal sprays, pills, and liquids. They don’t relieve other allergy symptoms such as itching and sneezing. Moreover, the patient should not use decongestant nose drops and sprays for more than a few days as long use of these medicines can lead to even more congestion and swelling of the nasal passages.
Immunomodulators: These are topical medications used to treat skin allergies. They are often used if other agents are ineffective or intolerable.
Autoinjectable epinephrine: This is used to treat a life-threatening allergic reaction known as anaphylaxis, which may be caused by severe allergic response to foods, drugs, or insect stings.
Specific Allergen Immunotherapy (AIT)
While all of the medications that are available today for allergies control the underlying symptoms of allergies, but when those medications are stopped, the symptoms will come back.
Another treatment strategy is to induce tolerance to the allergens by allergen-specific immunotherapy (AIT). The aim of AIT is to induce tolerance to the allergens, with resolution of allergen-induced inflammation and symptoms.
AIT triggers multiple mechanisms, which are sequentially activated. These events lead to multifaceted clinical improvement. Rapid desensitization to allergen, long-term allergen-specific immune tolerance as well as the suppression of allergic inflammation appears. AIT – allergen immunotherapy; Breg = B regulatory cell; Th = T helper cell; T reg = T regulatory cell.
Allergen-specific immunotherapy (AIT) involves repeated, systemic administration of allergen extracts to allergic individuals and results in sustained relief from symptoms caused by allergen exposure. This is, in turn, attributed to modifications in the immunologic response to the allergen. According to WHO, AIT is the only treatment that can affect the natural course of allergic diseases, and it can also prevent the development of asthma in patients with allergic rhinitis and stop the emergency of new sensitizations among atopic patients. It is the only treatment for allergy considered to target the cause of the disease and will potentially offer long-term effect, i.e. patient can remain symptom free after stopping the treatment.
Clinical improvement with AIT does not occur immediately. It usually requires at least 5 to 6 months before symptoms improve, sometimes longer. It is recommended that AIT is continued for about 3-5 years, to reduce the likelihood that the allergies will return. Whilst undergoing AIT, the patient still need to use his allergy medications and he should continue the asthma medications at the same time in the usual way.
Allergen immunotherapy (AIT) has been in use since more than one century, when Leonard Noon experimentally proved its efficacy in hayfever (Noon, in Lancet 1:1572-3, 1911). Since then, AIT was administered only as subcutaneous injections (SCIT) until the sublingual route (SLIT) was proposed in 1986. A number of studies published in the last 20 years have shown that very high dose sublingual immunotherapy (SLIT), where allergen extracts (tablets, sprays or drops) are retained under the tongue for a few minutes, then swallowed, can also be as effective as SCIT, but with a much better safety profile. SLIT was tested in very large clinical trials, including thousands of patients and with dose-ranging experimental designs. In parallel, the knowledge on the mechanisms of action of AIT was rapidly refined, leading to further improvements, such as the chemically modified extracts and the use of adjuvants to enhance efficacy and safety. In addition, in the last 10 years, there has been an increasing scientific and clinical interest in AIT applied to food allergies, in particular in children, with the use of orally administered extracts (Albin and Nowak-Węgrzyn, Immunol Allergy Clin North Am 35: 77-100, 2015). The results are so far encouraging, at least for cow’s milk, egg, and peanut, although the use of treatment is still restricted to clinical trials or within specialized centers. Finally, the introduction of molecular- or component-resolved diagnosis has allowed detailing the prescription of AIT, by better delineating true sensitization versus cross-reactivity (Canonica et al. in World Allergy Organ J 6(1):17, 2013). This latter point is also in strict relation to the use of recombinant, engineered or highly purified molecules, instead of raw extracts, for the desensitization process.
Other New Developments
IgE-mediated allergies today affect up to 30 % of the population in industrialized countries. Allergen immunotherapy is the only disease-modifying treatment option with a long-term effect. However, very few doctors in the past (<5 %) prescribe immunotherapy, due to their lack of the relevant knowledge and the concerns in handing possible local and systemic allergic side effects of subcutaneous administrations. The latter occur when an allergen accidentally reaches the blood circulation. Therefore, the ideal application route for allergen immunotherapy should be characterized by two hallmarks: firstly, by a high number of potent antigen-presenting cells, which enhance efficacy and thus shorten treatment duration. Secondly, the allergen administration site is ideally non-vascularized, so that inadvertent systemic distribution of the allergen and consequent systemic allergic side effects are minimized. In addition, it should be convenient for the patient, i.e., self-administrable and painless.
To improve the safety of AIT, inadvertent allergen delivery to the blood vasculature must be avoided. Ideally, the allergen should be delivered to a non-vascularized tissue. In certain ways, sublingual allergy immunotherapy (SLIT) fulfils this criterion, as the allergen is delivered to the oral mucosa, which is covered by a multi-layered epithelium.
Despite diffusion of the allergen down into deeper layers containing mast cells, which are responsible for the frequently observed local oral side effects, SLIT is considered very safe with respect to systemic allergic side effects. Apparently, diffusion into a vascularized layer is less risky than injection into a vascularized layer.
Novel therapies that interfere specifically with immunologic mechanisms underlying allergen-induced pathology are currently in clinical evaluation. Among these is anti-IgE, which directly targets IgE serum antibodies, thus inhibiting the central mechanism of immediate-type hypersensitivity reactions. Application of anti-IgE antibodies effectively reduces IgE serum levels regardless of allergen specificity. Anti-IgE therapy has been successfully tested in patients with allergic rhinitis, asthma, and food allergy, showing significant efficacy in reducing symptom scores and the use of rescue medications. However, such therapy is limited by high costs and the requirements for permanent or every-season treatment. The advantage of specific immunotherapy (SIT) is the potential to alter the course of the disease, which has been demonstrated in patients with allergic rhinitis, insect venom allergy and, to a lesser degree, asthma. The broader application of SIT is restricted by sometimes life-threatening adverse effects. The combination of anti-IgE with SIT was suggested to be superior to each single treatment protocol in children and adolescents with allergic rhinitis.
Other latest development or unproven treatment for allergy will be reviewed in the future here.