Comparison of the clinical efficacy and safety of subcutaneous and sublingual immunotherapy: methodological approaches and experimental results

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Abstract
Sublingual immunotherapy has been documented as clinically effective in controlled studies. Some concerns about the magnitude of disease severity reduction in relation to standard subcutaneous immunotherapy have been raised. The comparison with subcutaneous immunotherapy is important for giving recommendations on the use of sublingual immunotherapy in daily clinical practice. Only three controlled comparative studies of sublingual and subcutaneous immunotherapy have been published. The methodology of the studies indicated that some study design deficiencies limited the interpretation of efficacy. Only one study used an optimal placebo-controlled, double-blind, double-dummy and randomized design. The studies are assessed with respect to a sufficient number of patients to detect statistically possible differences, the inclusion of patients, clearly defined outcome measures, doses of extract administered, and duration of treatment. In all three studies the reduction in disease severity was of the order of 50% with no significant difference between the two treatments. The clinical efficacy of sublingual immunotherapy is based on three studies only, and a limited number of patients equal to the efficacy obtained by subcutaneous immunotherapy. Only limited information on long-term efficacy and preventative capacity are available. More data on these aspects are needed, but the restraint in using sublingual immunotherapy in the treatment strategy of allergic diseases does not seem to be evidence based. Future research should also focus on identifying which subsets of patients would most benefit from either of the two routes of immunotherapy administration.