I am an asthma patient.

Since the inhaler contains a medication (salbutamol), the use of it in the state of fasting will invalidate the fast. We advise you take medication at the time of Sahri to avoid an asthma attack. However, should you get the attack during fasting, if there is no adequate alternative which does not break the fast, you may use the inhaler and make-up for that fast later (make Qadhaa).