Three years of specific immunotherapy may be sufficient in house dust mite respiratory allergy.

Background: Specific immunotherapy (SIT) duration for respiratory allergy is currently based on individual decisions.

Objective: To evaluate the differences in clinical efficacy of SIT as a result of the duration between the current recommended limits (3-5 years).

Methods: A 5-year prospective, controlled clinical trial of SIT blind until the first year and randomization to a 3-year (IT3) or 5-year (IT5) course was conducted. Of the 239 patients with respiratory allergy caused by D pteronyssinus initially included, 142 completed 3 years of SIT with good compliance. Twenty-seven controls were included at the third year. Efficacy of SIT after 3 (T3) and 5 (T5) years was assessed by using clinical scores, visual analog scales (VASs), rhinitis (RQLQ) and asthma (AQLQ) quality of life questionnaires, skin tests, and serum immunoglobulins.

Results: At T3, significant reductions were observed in rhinitis (44% in IT3 and 50% in IT5; P < .001), asthma (80.9 % in IT3 and 70.9% in IT5; P < .001) scores, VAS (P < .001 in both), RQLQ (P < .001 in both) and AQLQ (P < .001 in both). At T5, the clinical benefit was maintained in both groups, and IT5 patients presented additional decreases (19%; P = .019) in rhinitis scores. At Tf, specific IgG(4) measurements were lower in IT3 (P = .03) without detecting differences in IT5. An increase in asthma score of 133% was the only difference observed in controls.

Conclusion: Clinical improvement is obtained with 3 years of D pteronyssinus SIT. Two additional years of SIT add clinical benefit in rhinitis only.