Background. Although allergen immunotherapy is effective for allergic rhinitis, its role in treating asthma is unclear. Methods. We examined the efficacy of immunotherapy for asthma exacerbated by seasonal ragweed exposure. During an observation phase, adults with asthma who were sensitive to ragweed kept daily diaries and recorded peak expiratory flow rates between July and October. Those who reported seasonal asthma symptoms and medication use as well as decreased peak expiratory flow were randomly assigned to receive placebo or ragweed-extract immunotherapy in doses that increased weekly for an additional two years. Results. During the observation phase, the mean (±SE) peak expiratory flow rate measured in the morning during the three weeks representing the height of the pollination season was 454±20 liters per minute in the immunotherapy group and 444±16 liters per minute in the placebo group. Of the 77 patients who began the treatment phase, 64 completed one year of the study treatment and 63 completed two years. During the two treatment years, the mean peak expiratory flow rate was higher in the immunotherapy group (489±16 liters per minute, vs. 453±17 in the placebo group [P=0.06] during the first year, and 480±12 liters per minute, vs. 461±13 in the placebo group [P=0.03] during the second). Medication use was higher in the immunotherapy group than in the placebo group during observation and lower during the first treatment year (P=0.01) but did not differ in the two groups during the second year (P=0.7). Asthma-symptom scores were similar in the two groups (P=0.08 in year 1 and P=0.3 in year 2). The immunotherapy group had reduced hay-fever symptoms, skin-test sensitivity to ragweed, and sensitivity to bronchial challenges and increased IgG antibodies to ragweed as compared with the placebo group; there was no longer a seasonal increase in IgE antibodies to ragweed allergen in the immunotherapy group after two years of treatment. Reduced medication costs were counterbalanced by the costs of immunotherapy. Conclusions. Although immunotherapy for adults with asthma exacerbated by seasonal ragweed exposure had positive effects on objective measures of asthma and allergy, the clinical effects were limited and many were not sustained for two years.
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