Introduction [edit]. A carboxyl group consists of a carbon double-bonded to an oxygen and also bonded to a-OH group. Compounds with carboxyl groups are called carboxylic acids or organic acids. The carboxyl group can act as an acid when by donating a proton (H +) to a solution and becoming ionized.
It therefore makes perfect sense to use the bronchodilator first, wait a few minutes, and then to use the steroid inhaler, after the airways have been opened up and are more relaxed. This way, the steroid can penetrate the lungs more effectively, and get down to decrease inflammation in your smaller airways.
Metered Dose Inhaler (MDI). This type of inhaler uses a small canister of medicine inside a plastic holder. The medicine in the canister is under pressure. As you press on the canister, a small burst (a metered dose) of medicine is sprayed out of the canister. Most people call this a  puff  of medicine. Your doctor will tell you the number of puffs (inhalations) to use, for example one or two puffs for each dose.