Dosing of European sublingual immunotherapy maintenance solutions relative to monthly recommended dosing of subcutaneous immunotherapy

Background: Recently, a series of assays has been conducted in which sublingual immunotherapy (SLIT) maintenance extracts of European manufacturers were compared with U.S. concentrated extracts by using U.S. Food and Drug Administration recommended in vitro testing. These test results have been published. We herein performed further data analysis to facilitate interpretation of SLIT dosing by U.S. physicians. Objective: To express the allergen quantity of maintenance SLIT as recommended by European manufacturers relative to U.S. subcutaneous immunotherapy (SCIT) maintenance dosing. Methods: We analyzed the maintenance SLIT solutions of Dermatophagoides pteronyssinus, timothy grass pollen, cat, and ragweed pollen from four European manufacturers and concentrated extracts from three U.S. manufacturers and from the U.S. Food and Drug Administration. Here, we expressed the potency of these European SLIT solutions in U.S. terms and from there calculated the monthly maintenance dose relative to the recommended monthly SCIT doses per allergen. Results: Over the whole range of allergen extracts analyzed here, one of the manufacturers consistently dosed low ("EUR1," monthly SLIT dose 1-5 times the SCIT dose) and one of the manufacturers dosed high ("EUR4," monthly SLIT dose 16-237 times the SCIT dose). Discussion: For more than half of the products, SLIT was not "high dose" as has originally been recommended. When reviewing the low-and high-dose products with respect to efficacy in clinical trials included in a meta-analysis on SLIT, some low-dose extracts showed efficacy. Thus, apart from the allergen dose, it might very well be possible that other factors also play an important role in determining clinical efficacy in SLIT.