SELECTED ARTICLES FROM THE RECENT LITERATURE 2004

12/10/04

Sublingual immunotherapy reviewed

Summary
Background - Allergy injection immunotherapy (IIT) significantly reduces symptoms and medication requirements in allergic rhinitis (AR). However, its use has been limited in some quarters by concerns about severe systemic allergic reactions which occur occasionally in IIT. There has been considerable interest in alternative routes of immunotherapy, particularly sublingual immunotherapy (SLIT).

Findings - Wilson et al of the University Hospital in Birmingham, UK carried out a review of 22 randomized, parallel group clinical trials (n=179 patients) comparing SLIT to sublingual placebo in the treatment of AR. An analysis of the findings in these studies was carried out by the method of standardized mean differences (SMD) using a random effects model.

They found considerable heterogeneity in the findings, likely because of varying methods used to administer the SLIT and different clinical response scoring systems employed. However, overall SLIT therapy was followed by a significant reduction in mean symptom scores (p=0.002) and medication use (p=0.0003) when compared to placebo therapy. There was no significant difference in response with use of different allergens in the different SLIT studies. The total amount of allergen delivered may be a determinant of SLIT success but the increasing time duration of SLIT did not clearly increase efficacy. SLIT did not appear to be effective in studies limited to allergic children; however, the numbers of children in such studies were too small to draw definitive conclusions.

Reference
Allergy 2005;60:4-12

Editor's Comments
There has been increasing interest in and trials of SLIT in Europe with apparently less intense interest in this approach in the USA. Some investigators have raised concerns about local adverse reactions to SLIT in the oral mucosa. This sort of problem has apparently not been frequent or a major obstacle in the studies reviewed. One might also be concerned about the inability to arrest systemic absorption of allergens introduced by SLIT in case of a systemic reaction (no tourniquets can be applied in the oral cavity!). However, systemic reactions have reportedly also not posed a major problem with SLIT.

It would be interesting to see the results of a careful comparison of the efficacy of SLIT vs IIT (using the same allergen) vs placebo in a parallel-group study of patients with similar baseline SAR. However, the logistics involved in a double-blind, double-dummy protocol to make valid comparisons would be a sizable challenge.

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