Dose counting and the use of pressurized metered-dose inhalers: running on empty

Pressurized metered-dose inhalers (pMDIs) are the cornerstone of asthma treatment. The pMDI is an economic and portable medication delivery system, but the device does not indicate how much medicine remains in the canister once a patient starts using it.

To determine how patients evaluate the contents of their pMDI and whether they are either discarding inhalers when medication remains or using inhalers beyond the indicated number of doses.

This study was conducted in April 2003 via a 6.5-minute telephone interview with a random sample of 500 families with asthma from across the United States.

Of the 500 respondents participating in the telephone interview, nearly one third (31.6%) named an inhaled corticosteroid or bronchodilator and inhaled corticosteroid combination as the inhaler used when wheezing, coughing, or short of breath. Respondents using a bronchodilator (n = 342) varied in the frequency with which they use their pMDIs: 31.9% daily, 18.7% weekly, 23.4% monthly, and 23.1% less than once per month. More than half (53.8%) of bronchodilator users refill their prescriptions more frequently than recommended by national guidelines. Only 36% of bronchodilator users reported ever having been told to keep track of pMDI doses used. Of those, 79% had been advised to do so by a physician, 6% by a pharmacist, and 3% by a nurse. Eighty-seven (25%) of the 342 respondents who named a bronchodilator reported having found their pMDI empty during an asthma exacerbation. Seven of those patients had to call 911. Of these 87 patients, 71 (82%) considered their pMDI empty when absolutely nothing came out.

Patients do not have a reliable means of monitoring the contents of their metered-dose inhalers, which is causing serious problems that need to be addressed. Given the necessity of a reliable dose counting method, it is clear that manufacturers should include dose counters as a standard feature of every metered-dose inhaler.