Sublingual immunotherapy or SLIT, is a method of administering allergy vaccines orally. With SLIT, the patient self-administers drops under the tongue, holds them under the tongue for 20-30 seconds and then swallows the drops. The oral vaccines work best under the tongue but the vaccine is effective when applied anywhere inside the mouth (so when treating a baby, it is enough to administer inside the mouth).
Because of its safety profile, SLIT is administered at home, avoiding weekly visits to the doctor’s office. Therefore, it is the ideal treatment for very young patients (in which weekly shots become a nuisance) and also for patients with asthma that are the patients that potentially can develop a reaction to allergy shots. SLIT also is very useful for the patient with busy schedules, erratic schedules or the ones that travels often and therefore cannot come to the office on a regular basis. Patients on weekly shots that plan to take a long trip can continue treatment by switching to SLIT. Upon their return, they can opt to go back to shots or to remain with SLIT.
Dr. Saporta has worked with oral vaccines since 2003. In 2007 he published a method of administration that is extremely effective and better tolerated than many other methods.
To administer SLIT, an oral vaccine needs to be prepared based on the results of an allergy test. The vaccine will contain all allergens to which the patient showed reactivity during the test. In other words, the vaccine is customized for each patient according to each patient’s test results.
History of SLIT
SLIT is probably the oldest method of administering allergy vaccines. While the first paper on injectable vaccines was published in 1911, the first paper on oral vaccines was published in 1900.
SLIT was commonly used in the US until the 1970’s when interest in its use faded for no clear reasons. Interest about SLIT developed in Europe after a series of deaths occurred in England in 1986 as a consequence of administration of injectable allergy vaccines (“allergy shots”). Since that time, the amount of research done in Europe on oral vaccines is so large that there is the impression that SLIT was originally described in Europe when the reality is that SLIT was first described in the US.
Different Methods of Immunotherapy Administration
When allergy treatments first developed, the allergens that were used for testing and treatment were diluted in a 1:10 ratio. In 1935, Dr. Herbert Rinkel experimented with 1:5 dilutions and he observed that when using 1:5 dilutions, the intradermal test (skin test) was better tolerated and the treatment results were better. A small group of allergists incorporated the 1:5 dilution system for the administration of injectable vaccines but for oral vaccines the 1:10 dilutions system continued in use. According to different technique, the number of drops per does could be as large as 20 and the dose could be held under the tongue from one to several minutes. Doses were administered from once a week to several times per week.
Dr. Saporta devised a method of sublingual administration using 1:5 dilutions that also incorporated the concepts of daily administration and slow incremental increases of the treatment dose. The dose is never larger than 5 drops which are easily held under the tongue and for no more than 30 seconds. This allowed better compliance and better results. Slow dose progression also allows for easy recognition of reactions to sublingual immunotherapy.
Problems with sublingual immunotherapy
Contrary to injections, oral vaccines are extremely safe. To administer injections the patient needs to understand that a severe reaction, even though rare, can develop after the injection. Any patient undergoing allergy testing with injections or allergy treatments with injections should carry an autoinjector of adrenaline -usually an EpiPen® or similar device- for 24 hours after the test.
Such precautions are not necessary for oral vaccines. However, this does not mean that oral vaccines are problem-free. In general, the problems reported about SLIT administration are classified as local (oral itching) or systemic (gastro-intestinal -GI- symptoms).
After analyzing problems occurring after SLIT administration for many years Dr. Saporta concluded that the problems can be related to the allergen(s) or to the diluent (Glycerin).
Problems related to the allergen
If the dose of allergen delivered to the patient is too strong for that patient, some symptoms can develop. These include itching usually at the oral area (lips, oral mucosa or tongue), itching in the throat, cough or rarely diffuse skin itching.
These problems are managed by decreasing the allergenic dose and once the symptom resolves treatment progresses as planned. Having a good quality allergy test decreases the frequency of these problems.
Problems related to glycerin
The diluent used for SLIT is Glycerin. Glycerin is a solvent that is used in standardized allergen extracts as it stabilizes the proteins contained in the allergens. It has a sweet flavor therefore it is ideal as a vehicle for oral vaccines. Glycerin is extremely common, contained in many household and food items. When a patient is reactive to Glycerin, it is possible to develop symptoms when glycerin is administered on a daily basis in SLIT. In these cases, the symptom(s) persist despite dilution of the formula and the problem(s) gets worse over time as Glycerin intake continues.
Symptoms that can occur due to Glycerin include diffuse itching or urticaria, headaches, gastrointestinal (GI) problems including stomachache, nausea or even vomiting. This type of reactivity is described in the literature as systemic reactions to SLIT. Dr. Saporta realized that the reactions considered as “systemic reactions to SLIT” were actually a reaction to the Glycerin in the solution, when he observed that when the drops were diluted in saline the problems resolved. In support of this observation is a fact about Oral Allergy Tablets, that have been introduced into the allergy market recently. Allergy Tablets do not contain Glycerin as they do not need a liquid solvent. Even though these tablets have a high incidence of different adverse events, GI problems are not listed as one of the problems.
Cooperation between large pharmaceutical companies and allergen manufacturing companies led to the development of “Allergy Tables”.
Allergy Tablets rapidly dissolve as soon as they are placed in the mouth. The tablet carries one or just a few related allergens (for example two different dust mites, or a few different species of ragweed pollen).
The concentration of allergen in these tablets is always the same. In other words, regardless of the level of reactivity of the potential patient, the treatment is always with the same dose. The concept of “one size fits all” is used, lacking a starting dose and an up-dosing schedule. Therefore, the allergenic dose provided by these allergy tablets is potentially too much for patients that are very sensitive (highly reactive) and at the same time the dose could be too small for patients that only react to a large dose of allergen.
Because of the first problem (dose too large for some patients) the allergy tablets are known to have a high percentage of adverse events. Because these adverse events can potentially be severe, the FDA requires that the information sheet of the allergy tablets carry a black-box warning requiring the patient to carry an Epi Pen® or similar device while administering these tablets.
Because of the second problem (dose is potentially too small for some patients), the allergy tablets do not work for many people.
While Sublingual Immunotherapy is in use since the late 1800’s, the development of the allergy tablets is relatively recent (first allergy tablet came into the market in 2014).
There are 2 interesting facts about this topic:
- When reading present day articles about immunotherapy provided orally, the articles refer to the use of SLIT (Sub lingual Immunotherapy) and it is difficult to understand that often the articles are referring to the use of allergy tablets. That type of treatment should be addressed as ATI for allergy tablet immunotherapy and not as SLIT that should be used when referring to the administration of oral drops under the tongue (Sublingual immunotherapy)
- Allergy tablets have been approved by the FDA for the management of allergic conditions, even though they carry a black-box warning. Their efficacy is potentially limited as, by the nature of their design, they cannot address the large number of different allergens to which the allergic patient usually reacts. The patient being treated with allergy tablets will at best develop immunity only against the allergen or few allergens contained in the tablet.
When Sub Lingual Immunotherapy (SLIT) is properly used, the patient will be safely treated with a highly effective vaccine that will contain all the allergens determined to be reactive in the individual patient according to the results of the allergy test. SLIT provides individualized treatment that will help the particular patient being treated. Certainly, the type of test will determine how many allergens are diagnosed and therefore the difference in treatment results.
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