Immunotherapy is the practice of administering gradually increasing doses of an allergen extract (e.g. pollen) in order to reduce the symptoms of hayfever or asthma that it causes. It was first carried out almost 100 years ago and is now in widespread use around the world. It is sometimes referred to as ‘allergy vaccination’ or ‘desensitisation’. Until recently, immunotherapy involved having a series of injections (subcutaneous immunotherapy) over a period of three to five years. Injections needed to be given in hospital and close observation was required for an hour after each ‘shot’, because of a small risk of a severe allergic reaction.
Instead, sub-lingual Immunotherapy (SLIT) entails the placing of drops or tablets under the tongue. We make use of various products. Whilst these are licensed for use in many countries, this is not the case for most products we use and certainly not in children less than 12 years of age. Nonetheless, the products can be used on a name patient basis and enjoy an excellent safety record.
SLIT is also available for allergies to House Dust Mite (although subcutaneous therapy is also possible when all the indications are met) if there is no appropriate response to house dust mite reduction measures.
The logistics and reality of taking a daily product, every day, for three years needs to be carefully considered before commencing SLIT. The financial and time costs are not insignificant but this remains the only disease modifying therapy.
SLIT is very safe and means that injections are not needed. However, it needs to be taken on a daily basis. Therapy is typically initiated in clinic but then continues at home. The medication is kept under the tongue for at least 1 minute before swallowing. Children are generally only able to comply with this demand from around 6 years of age (it is both frustrating and expensive if children refuse the medications).
The most common side effects are itchiness and swelling in the mouth after taking the medicine. This can be helped by taking antihistamines beforehand, or if the symptoms are recurrent, reducing the dose. Side effects are very rarely troublesome enough for the patient to stop the treatment.
Study: Determination of the Optimum Duration of SLIT to House Dust Mite
To investigate the long-term effects of SLIT, and the optimal duration of treatment, the researchers studied 78 patients aged 18-65 years, with allergic rhinitis (with or without asthma), who were monosensitized to dust mites. The participants were divided into four groups to receive mite-specific SLIT plus drug therapy for 3 (n=19), 4 (n=21), or 5 years (n=17), or drug therapy alone (controls; n=21). Clinical benefit, based on the frequency and severity of symptoms, were assessed every year during the winter months over a follow-up period of 15 years. During this time, 10 patients receiving SLIT and nine controls dropped out of the study. There was no significant change in clinical scores among the 12 controls. In patients receiving SLIT, a significant clinical benefit was observed after just 1 year, which persisted for 7 years among patients who received SLIT for 3 years, and 8 years among those who received SLIT for 4 or 5 years. After loss of clinical benefit, patients in the SLIT groups received a second course of treatment, and this induced a benefit more rapidly than the first course. All patients in the control group developed a new skin sensitization during the follow-up period compared with just 21%, 12%, and 11% of patients who received SLIT for 3, 4, and 5 years, respectively. They concluded that under the present conditions, it can be suggested that a 4-year duration of SLIT is the optimal choice because it induces a long-lasting clinical improvement similar to that seen with a 5-year course and greater than that of a 3-year vaccination.
A 4-year course of sublingual immunotherapy (SLIT) would be the optimum duration for allergic rhinitis patients sensitized to dust mite allergens. Marogna M, Spadolini I, Massolo A et al. Long-lasting effects of sublingual immunotherapy according to its duration: A 15-year prospective study. Journal of Allergy and Clinical Immunology 2010; 126(5): 969-975.