The goal of this observational study is to assess the response to treatment, in patients 18 years and older diagnosed with severe asthma in whom an IL5/IL5R antagonists was initiated between 2012 and 2020.

The main question[s] it aims to answer are:

• What is the response rate after one year of treatment with IL5/IL5R antagonists.
• What is the response and remission rate after one year of treatment with IL5/IL5R antagonists in subjects who fullfilled the original randomized control trials (RCTs) inclusion criteria compared with those who did not.

IL5/IL5-receptor (IL5R) antagonists are effective in reducing asthma exacerbations and have a corticosteroid sparing effect in selected severe eosinophilic asthmatics. The original randomized clinical trials that assessed the efficacy of IL5/IL5-R antagonists included highly selected patients who are not necessarily representative of the asthmatic population treated with IL5/IL5R antagonists in clinical practice.

The aims of this study are:

1. To assess the response to treatment, in patients 18 years and older diagnosed with severe asthma in whom an IL5/IL5R antagonists was initiated between 2012 and 2020.
2. To compare the response and remission rate after one year of treatment with IL5/IL5-R antagonists in asthmatics who would and would have not met the inclusion criteria of the original randomized clinical trials.

We will perform a retrospective cohort study using data from the hospital charts of severe asthmatics treated with mepolizumab, reslizumab or benralizumab between November 2012 and December 2020 at the outpatient asthma clinic of a tertiary center (Sacre-Coeur Hospital) in Montreal. Cohort entry (CE) will be defined as the first prescription filled of IL5/IL5R antagonists. Authorization from the research ethics committee of the CIUSSS du Nord-de-l'île-de-Montréal and from the director of Professional Services was obtained.

Statistical analysis Descriptive statistics will be used to summarize clinical, functional, and demographic characteristics of the patients of the whole cohort, as well as of the RCT in group and RCT out group. Baseline data will be recorded on the date closest to cohort entry. Results will be expressed as mean and standard deviation, except for data with a non-normal distribution, which were expressed as median and interquartile ranges and proportions for categorical variables. Chi-squared test and Student's t test will be used to compare patients' characteristics between RCT in group and RCT out group. All tests will be two-tailed, and the statistical significance level will be set at 0.05.

Logistic regression analyses will be performed to identify factors associated with a positive response to treatment as well as the achievement of remission on treatment.

Inclusion Criteria:

All patients 18 years and older diagnosed with severe asthma in whom an IL5/IL5R antagonist was initiated at the outpatient asthma clinic of a tertiary center (Sacre-Coeur Hospital) in Montreal.c between 2012 and 2020.

Exclusion Criteria:

None

Patients 18 years and older diagnosed with severe asthma in whom an IL5/IL5R antagonist was initiated between 2012 and 2020 for were included. Data recorded in the year preceding the initiation of IL5/IL5R antagonist were compared with data recorded in the year following the initiation of the biological therapy.

Subjects who were aged 75 years or younger, had a smoking history of less than 10 pack-year, a FEV1 of less than 80% of the predicted value along with FEV1 reversibility of at least 12% and 200 ml in the previous year were considered as fulfilling the inclusion criteria of the original RCTs (RCT in group). Subjects who did not meet one of those criteria were considered as not fulfilling the original RCT inclusion criteria (RCT out group).

Adverse event were not collected

This is a retrospective chart review, adverses events were not collected.