Metered Dose Inhalers Don't Reveal When They're Empty and Patients Suffer
The most common way patients are instructed to monitor remaining medication in their inhaler is by counting down the number of puffs left, which was ineffective for many patients that use inhalers infrequently. Most patients don't count, and insteade consider their inhaler empty when no more puffs come out. Unfortunately, they don't realize that the inhaler only delivers medicine for a certain number of puffs, then afterwards, continues to appear to puff but only is releasing the propellant and pressurized air without any medication. Either situation is dangerous, since the patient doesn't have access to the medication that can save them from more serious immediate breathing problems. In the Annals article, 25% of respondents thought their inhaler was empty when it stopped puffing, and 7 had to call 911 because they couldn't manage their breathlessness with an empty inhaler.
As an allergist's son, I also remember years back when he instructed patients to discard their inhalers when they don't float in water, but now that's been found to be unreliable to see if medication remains due to the remaining pressurized propellant.
The article and accompanying editorial support a counter that would instruct patients how many doses of medication remain. The way it could work is by a mechanism similar to that of a medication i had to use after a chronic cough last year - advair. Although advair (salmeterol/fluticasone) is a delivered as an inhaled powder, it has a counter to let me know how many doses remain. That way I can call for a refill if I needed it, especially with the delay in delivery from my insurance company's mail-order pharmacy which is a lot cheaper, and is willing to provide 3 month refills rather than 1.
1. Sander; Chipps
Dose counting and the use of pressurized metered-dose inhalers: running on empty
Annals of Allergy, Asthma and Immunology, Vol. 97, No. 1, pp.34-38