The Environmental Exposure Unit: a system to test anti‐allergic treatment
Authors: Day J. 
Published: November 2003

Background  The Environmental Exposure Unit (EEU) is an indoor pollen exposure system designed to evaluate the efficacy and especially the onset of action of antiallergic medications. Some of the unpredictable factors that are associated with outdoor studies, which influence pollen levels are controlled using this system and antiallergic treatment can be assessed under conditions of predetermined uniform pollen levels sustained over designated time periods.

Objective  The aim of this study was to determine the onset of action and efficacy of cetirizine 10 mg OD, loratadine 10 mg OD and placebo in allergic subjects exposed to ragweed pollen in the EEU, using a study identical in design to a previously conducted EEU study and from the results to substantiate the EEU as an effective test system of antiallergic medication.

Methods  The onset of action and efficacy of cetirizine and loratadine on the symptoms of seasonal allergic rhinitis in subjects challenged with ragweed pollen in the EEU, were investigated in two separate randomized, placebo‐controlled, double‐blind, parallel‐group studies of identical design. In the first study (1995), a total of 202 subjects were randomized to cetirizine (n = 67), loratadine (n = 67) or placebo (n = 68). Subjects meeting inclusion/exclusion criteria were exposed to ragweed pollen in the EEU to activate allergic symptoms (priming phase) and those with qualifying symptoms returned for the treatment phase. Subjects attaining qualifying symptoms during the first 1.5 h of the baseline period of the treatment phase were randomized to receive a single daily dose of either cetirizine 10 mg, loratadine 10 mg or placebo on days 1 and 2. During the treatment phase, subjects were challenged to ragweed pollen (7 h on day 1, 6 h on day 2) and symptoms were recorded at half‐hourly time points. This study was repeated using a larger number of subjects (n = 360) in 1999 with an identical design.

Results  In both studies, cetirizine produced significant symptom improvement at 1 h compared with both loratadine and placebo. Cetirizine continued to reduce Total Symptom Complex (TSC) and Major Symptom Complex (MSC) scores at nearly all half‐hourly time points after onset of action for the 1995 study, and at all time points vs. placebo and at most time points vs. loratadine after onset of action during the 1999 study. The onset of action for loratadine was 3 h compared with placebo and loratadine significantly reduced symptoms postdosing on day 1 in both studies. The 24 h duration of effect of cetirizine was evident in both studies after 1.5 h of pollen exposure on day 2, which was not observed with loratadine. Cetirizine produced a significantly greater percentage change in MSC and TSC scores at 24 h compared with both loratadine and placebo in the 1995 study and in MSC scores in the 1999 study.

Conclusion  Cetirizine acted earlier and was more effective than loratadine and placebo in reducing symptoms of seasonal allergic rhinitis in subjects undergoing controlled ragweed pollen challenge in the EEU. The onset of action for cetirizine was 1 h compared with 3 h for loratadine. Similar results were observed in both studies that not only confirmed medication performance but validated the EEU as a test system for the determination of onset of action and short‐term efficacy of antiallergic medications.