Background: To evaluate the long-term safety of subcutaneous immunotherapy with TO-204, a standardized house dust mite (HDM) allergen extracts, we conducted a multicenter, open label clinical trial. Methods: Japanese patients aged 5–65 years were eligible for the study, if they had HDM-induced allergic rhinitis (AR), allergic bronchial asthma (BA), or both. TO-204 was administered in a dose titration scheme, and the maintenance dose was determined according to the predefined criteria. The treatment period was 52 weeks, and patients who were willing to continue the treatment received TO-204 beyond 52 weeks. This clinical trial is registered at the Japan Pharmaceutical Information Center (Japic CTI-121900). Results: Between July 2012 and May 2015, 44 patients (28 with AR and 16 with allergic BA) were enrolled into the study. All patients were included in the analysis. The duration of treatment ranged from 23 to 142 weeks and the median maintenance dose was 200 Japanese allergy units (JAU). Adverse events occurred in 22 patients (50%). The most common adverse event was local reactions related to the injection sites. Four patients experienced anaphylactic reactions when they were treated with the dose of 500 JAU. Two patients experienced anaphylactic shock with the doses of 1000 JAU at onset. These 6 patients could continue the study with dose reduction. Conclusions: Safety profile of TO-204 was acceptable in Japanese patients with HDM-induced AR or allergic BA. Higher doses should be administered carefully, because the risk of anaphylaxis increased at doses of 500 or 1000 JAU.
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