Sublingual Immunotherapy, SLIT or “allergy drops”, continues to be a hot topic in the allergy community. There continue to be questions about its effectiveness and its exact role in allergy treatment. A couple of recent articles have added to the debate.
The first article looked at SLIT using one allergen vs. SLIT with multiple allergens. This has always been a big question regarding SLIT use in the U.S., since most U.S. allergy sufferers are allergic to multiple different allergens. In this trial, they took people with grass pollen allergy and put them on SLIT containing either just grass pollen or grass pollen and several other allergens. At the end of the trial, neither group showed any difference in symptom scores or medication use, though the grass pollen alone group did better in some secondary measures. This trial reiterates the difficulties U.S. researchers have had replicating the overwhelmingly positive results of the southern European researchers. It calls into question whether SLIT will be widely adopted in the U.S.. If multi-allergen SLIT is ineffective, then it will not be appropriate for the majority of U.S. immunotherapy candidates.
The second paper reviewed the several meta-analyses published regarding SLIT. A meta-analysis takes numerous studies and pools their information to try and achieve higher statistical certainty regarding the subject. MAs can be helpful, but they are not the ultimate answer some claim them to be. Often the studies they use are very different in terms of patient selection, interventions, methodology, and endpoints. They also suffer from the GIGO problem: garbage in, garbage out. In other words, pooling a bunch of poorly done studies does not make for one good study.
In any event, this review of 5 MAs looking at SLIT found numerous inconsistencies among the MAs. That is, when different MAs used data from the same trial, they reported different outcomes from the trial. This is a big red flag and signals that the MA authors were either altering the data to fit their predetermined conclusions or were being inexcusably sloppy. The reviewers also noted probable “publication bias”, where positive studies get published and included in MAs, but negative trials get ignored and never published. Despite all this, the reviewers conclusion was that there was not sufficient evidence to recommend SLIT at this time.
We at the AAAMT have about 20 patients currently on SLIT, versus over 1000 on traditional allergy shots. I’ve been brutally honest with SLIT patients regarding my healthy skepticism for the long-term prognosis of SLIT. In my opinion, the jury is still out on SLIT and I will continue to recommend it only in rare circumstances.