[Allergen-specific immune therapy in the treatment of asthma]

1. To identify all published randomised controlled trials of allergen specific immunotherapy in asthma. 2. To estimate the overall efficacy of allergen specific immunotherapy upon asthmatic symptoms, medication requirements, lung function, nonspecific bronchial hyperreactivity (BHR) and allergen specific BHR.

A search of the asthma database by the Cochrane Airways Group at St. Georges Hospital Medical School, London identified 660 nonunique citations with the keywords Immunotherapy* or Hyposensitive or Desensiti*. This database included all studies published up to 1997 with the keywords Asthma or Wheez* from the Medline, Embase and Cinahl databases, together with other studies identified by handsearching.

The review was restricted to randomised controlled trials (RCT). Only studies which focussed upon asthma were included. Allergen specific immunotherapy was defined as the subcutaneous administration of extracts of house dust mites, pollens, animal danders or moulds, chemically modified allergoids or antigen-antibody complexes. Although placebo controlled trials were methodologically stronger, studies which administered house dust or other relatively antigenically inactive preparations to the control group were also considered. Double blinded trials were preferred, but single blind and open studies were also reviewed for possible inclusion. At least one of the following clinical outcomes had to be reported: asthmatic symptoms, asthma medication requirements, lung function, nonspecific BHR or allergen specific BHR. Inclusion of studies in the review was decided by a simple majority of all three reviewers, who independently read the methods sections of papers identified by the search strategy and applied the stated criteria. Quality assessment was performed by 2 reviewers, who independently assessed the concealment of allocation.

The comparisons were: Allergen immunotherapy v placebo, Allergen immunotherapy v antigenically inactive control, House dust v placebo and Allergen immunotherapy v untreated control. These comparisons were performed separately for each outcome, whenever these results were reported. Outcome data were extracted and entered into RevMan 3.0.1 for statistical analysis. Categorical outcomes were analysed as odds ratios (OR) and 95% confidence intervals (95% CI) calculated by Peto's method. Continuous outcomes were analysed as standardised mean differences (SMD). Fixed effects models were used to obtain summary statistics for the overall efficacy of allergen immunotherapy and x2 tests were performed to assess heterogeneity between studies.

Fifty four randomised controlled trials published between 1954 and 1997 satisfied the inclusion criteria. There were 25 studies reporting immunotherapy for mite allergy, 13 studies of pollen allergy, eight studies of animal dander allergy, two studies of allergy to the mould Cladosporium and six studies which attempted simultaneous immunotherapy for multiple aeroallergens. Concealment of allocation was assessed as clearly adequate in only 11 studies. The adequacy or otherwise of 40 studies could not be determined from the details published in the papers. Only three studies used a clearly inadequate method for concealment of allocation. There was a significant overall improvement in asthma symptom scores following immunotherapy (combined SMD -0.52; 95% -0.70 to -0.35). Patients randomised to immunotherapy were also significantly less likely to report a deterioration in asthma symptoms than those randomised to placebo (OR 0.27; 95% CI 0.21 to 0.35). Asthma medication requirements were significantly reduced (SMD -0.51; 95% CI -0.74 to -0.28). Patients randomized to immunotherapy were also significantly less likely to require medication than those randomised to placebo (OR 0.28; 95% CI 0.19 to 0.42). There was no overall improvement in lung function following immunotherapy and marked hete