Enhanced Efficacy of Dust Mite Sublingual Immunotherapy in Low-Response Allergic Rhinitis Patients after Dose Increment at 6 Months: A Prospective Study

<b><i>Background:</i></b> Several studies have suggested that sublingual immunotherapy (SLIT) involves a dose-response relationship and inadequate dosage might not achieve a favorable clinical effect. <b><i>Objective:</i></b> The aim of this prospective study was to investigate the efficacy and safety of increasing SLIT dosage at 6 months in patients with house dust mite-induced allergic rhinitis (AR) who had low response to treatment. <b><i>Methods:</i></b> A total of 157 AR participants aged 4–60 years were enrolled and received SLIT with <i>Dermatophagoides farinae</i> drops. After 6 months of SLIT, patients were interviewed and then classified into a high-response (HR) group and a low-response (LR) group based on the combined symptom and medication score (CSMS) reduction rate. Patients with a CSMS reduction rate over 50% were defined as HR and continued the original dose, while patients with a CSMS reduction rate ranging from 20 to 50% were defined as LR and received an increased dose (percentage of dosage increment, 33.33% for patients aged &#x3c;14 years and 50% for patients aged ≥14 years). Patients with a CSMS reduction rate below 20% were considered nonresponse (NR) and recommended to withdraw from SLIT. CSMS, visual analog scale (VAS), and adverse events were assessed at 0.5, 1, 2, and 3 years during the 3-year treatment. <b><i>Results:</i></b> A total of 54 and 56 patients completed the treatment in the HR and LR groups, respectively. The CSMS and VAS of both groups decreased significantly at 6 months (<i>p</i> &#x3c; 0.05). Significant differences between the two groups were found in CSMS and VAS at 6 months and 1 year (<i>p</i> &#x3c; 0.05), but not in later follow-ups (<i>p</i> &#x3e; 0.05). The improvement of adults in the LR group was significantly lower than that of children at 6 months (<i>p</i> &#x3c; 0.05), but there was no difference in later follow-ups (<i>p</i> &#x3e; 0.05). There was no difference in CSMS or VAS in patients with monosensitization and polysensitization in the same treatment group at 1 year and in subsequent visits (<i>p</i>&#x3e; 0.05). Overall, 47 patients withdrew from this study due to NR (<i>n</i> = 22) and other reasons (<i>n</i> = 25). <b><i>Conclusions:</i></b> Six months might be a critical time point for efficacy assessment and dosage adjustment for AR patients after SLIT. In patients with low response, dosage enhancement within a certain range may enhance the effectiveness of SLIT.