Hello from JA
I have a much different opinion for you...clinical trials are not a first line approach here.
You have not mentioned
Pulmonary rehabilitation which is doctor can order.
Allergy testing and the desensitization to environamental components stimulating his asthma. Indoor air quality treatment. Working with an allergist immunologist. Working with a pulmonologist. You have not stated that he is impaired to the point of being a clinical trial candidate...and preventing this from progressing would be more important currently.
There are in addition to clinical trial medications, other therapies and forefront considerations from medicine....I can go into these in more detail
Let me know if you have further questions.
Please don't forget a positive rating.