Specific immunotherapy by the sublingual route for respiratory allergy

Allergic diseases have high and increasing world prevalence [1,2]. In particular, respiratory allergy is caused by sensitization to environmental aeroallergens such as pollens, house dust mites, moulds, and animal epithelia and is clinically expressed as rhinitis and asthma.The management of respiratory allergy relies upon, when possible, allergen avoidance, drug treatment, and allergen-specific immunotherapy (SIT) [3]. SIT is the practice of administering gradually increasing doses of the specific causative allergen to reduce the clinical reactivity of allergic subjects. SIT has central importance because of its ability to modify the natural history of the disease and to extend its effectiveness also after treatment withdrawal, provided it is administered for an adequate duration [4]. The subcutaneous route has been for decades the traditional route of administration, but in recent years the sublingual route emerged as an actual treatment option [5]. The main reason to introduce sublingual immunotherapy (SLIT) was the safety problems with subcutaneous immunotherapy (SCIT), which may include systemic reactions, sometimes severe and, though very rarely, even fatal [6].The first studies on SLIT used low allergen dosages [7,8] but it was soon apparent that doses much higher than those administered by SCIT were needed to ensure clinical efficacy. In consensus documents, an optimal dosage as high as at least 50 times the dose administered by injection was suggested [3], though this ratio may be not pertinent for all products.The high number of trials on SLIT conducted in recent years allowed an accurate evidence-based assessment of its effectiveness by several meta-analyses on the whole patient population as well as on subgroups defined by clinical expression (rhinitis and asthma) or age (adults and children) parameters [9-16]. At the same time, other studies evaluated important aspects defining the suitability of SLIT, such as the compliance and the cost-effectiveness.T