Background Modification of allergens by glutaraldehyde in extracts used for immunotherapy reduces the risk for side-effects, but the therapeutic efficacy of such extracts still requires further evaluation. The aim of this study was to show the efficacy and safety of immunotherapy with a single-strength glutaraldehyde-modified aluminium hydroxide-adsorbed extract of birch pollen.
Methods In a multi-centre, randomized, placebo-controlled double-blind setting, starting in 2001 between 1 August and 15 December, birch pollen-allergic subjects (n=62) were injected subcutaneously with increasing doses of the allergen extract or placebo at weekly intervals over a 6-week period (or longer if adverse reactions occurred). Maintenance dose was given monthly for at least 18 months till June 2003. Efficacy was evaluated on the basis of the clinical index score (CIS), a combined symptom and medication score.
Results Fifty-eight patients could be evaluated for clinical efficacy. Treatment with the birch pollen extract resulted in a lower CIS for the eye and nose during the peak birch pollen season of 2003, compared with placebo (reductions of 42% and 31%, respectively) (P=0.017 and 0.039). Active treatment induced IgG and IgG4 antibodies reacting with Bet v 1 (P<0.001). Sera from treated patients had a blocking effect on Bet v 1-induced basophil activation (P<0.04). No major adverse reactions occurred, and local reactions, if occurring, were mild.
Conclusion Immunotherapy with a modified slow-release birch pollen extract, administered in a single-strength preparation with a rapid dose increase, is safe and efficacious. IgG and IgG4 antibodies against native Bet v 1 are induced, which block basophil activation.