Subcutaneous immunotherapy versus sublingual immunotherapy: which is more effective?

Subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) are both effective treatments for allergic rhinitis and allergic asthma, both show clinical evidence of disease modification by decreasing new sensitizations in individuals who were monosensitized, by reducing the development of asthma in patients with allergic rhinitis, and by inducing clinical improvement that persists for years after discontinuation of a successful course of treatment. Initiation of SLIT is accompanied by a high incidence of local symptoms, but these are generally mild and do not usually persist beyond the first few weeks. Systemic reactions do occasionally occur with SLIT but much less frequently than with SCIT, and, to date, no fatal or near fatal reactions have been reported. Effective doses have been defined for many allergens for SCIT and are now being defined for SLIT. There remains the unanswered question of the effectiveness of SLIT with multiple allergen extracts. The relative clinical efficacy of SCIT and SLIT remains to be defined. When each is compared with placebo, results of meta-analyses suggest greater efficacy of SCIT. In the limited number of randomized, head-to-head studies, SCIT has more often provided greater clinical and immunologic responses. However, head-to-head studies with well-defined effective doses by the 2 routes are urgently needed.