It is easy to know when a DPI is empty because DPIs have incorporated dose counters that help you keep track of how many doses remain in the inhaler and remind you when to refill your prescription. Some dose counters count down as you use each dose or puff of medicine. Others count down every 10 doses. The Diskus device counts down each time you inhale a dose, and when five doses remain in the DPI, a red number 5 appears in the window, followed by a red 4, 3, 2, 1, and then 0. The Twisthaler device also counts down for you until “00” appears in the display. The Flexhaler counts down by ten—the display will not change after each puff—until zero is reached. It is a good idea to keep an eye on how many doses remain in your DPI so that you can refill your prescription before you run out of medicine. Never use a DPI when the dose counter reads zero.
Preloaded DPIs are dispensed by your pharmacist in a moisture-protective foil wrapper. The instructions for patients that come with the prescribed DPI will specify how long a DPI can be kept before it has to be replaced with fresh medicine. An Advair containing Diskus DPI must be discarded within 30 days of opening the foil wrapper, regardless of whether or not the counter registers 0 doses.
A Serevent Diskus DPI must be discarded within 6 weeks of opening the foil wrapper, regardless of how many doses of drug remain in the device. Simi-larly, Asmanex Twisthaler has to be thrown away after 45 days, even if the counter indicates that a few doses remain in the device.
Four MDIs available in the United States have built-in dose counters. The MDIs with incorporated dose-counters are Advair HFA, Flovent HFA, Symbicort HFA, and Ventolin HFA. The first three medications are daily use, control medicines, and the fourth is a quick-relief, short-acting β2 agonist bronchodilator. All four have dose counters that count down as you use up the medicine, making it clear when only a few doses remain in the device.
All MDIs contain active medicine and a propellant (HFA) as described in Questions 59 and 60. It is important to understand that once the active medicine has been used up, propellant may remain in the MDI canister. Even though no medicine remains in the device, it is not entirely empty. That is why you cannot tell if an MDI is empty by shaking it. Once you have used the number of medication doses contained in any MDI, you should dis-card it. If you continue to use that particular MDI (something I obviously discourage) you will be inhaling propellant!
If you have been prescribed Advair HFA, Flovent HFA, Symbicort HFA, or Ventolin HFA, the dose counters will let you know when a canister is out of medicine. If your MDI inhaler does not have an incorporated dose counter, the only way to be certain that an MDI still has medicine in it is to actually count each (and every) dose as you use the medicine. Small, external counters that fit in the palm of your hand can be clicked each time you use the MDI, an accurate but not always convenient solution. External dose counters that attach to MDIs are also on the market. Another option involves estimating ahead of time when you will need to replace the MDI.
Your estimate is based on how many doses (or actuations) the MDI contains and how frequently you use the MDI. For example, consider an MDI whose label states that it contains 100 puffs of medicine. If you take one puff of the medication twice daily the new MDI should provide enough medicine for 50 days; dividing 100 (the number of doses in the MDI) by 2 (the number of doses used in 1 day).
You can also ask your pulmonary doctor or pharmacist to help you anticipate when you will need to obtain an MDI refill. You divide the total number of doses in the full MDI by the number of daily doses you plan to use to determine for how many days the MDI will last. Consider writing the date in your calendar or PDA ahead of time so you remember to con-tact your pharmacist a few days ahead of the expected empty MDI date.
Various strategies have been advanced over the years to help you know when your MDI is empty or nearly empty. As noted above, shaking the inhaler is an unreliable method of assessing whether or not the inhaler still contains medication. Another idea that is not recommended involves removing the metal MDI canister from its plastic mouthpiece and dropping the canister into a glass of water to see if it floats near the surface, which would indicate that it is empty or nearly so.
MDI manufacturers and the NAEPP are strongly opposed to immersing the metal MDI canister in water, so floating any MDI canister is a no-no under any circumstances.
The potency of inhaled medications cannot be guaranteed if the canister is immersed in water. Finally, note that Ventolin HFA with an incorporated dose counter and Symbicort HFA, a quick-acting, rapid-relief bronchodilator and a daily-use controller medicine respectively, are packaged in moisture-proof protective pouches.
Once you open the pouch, each medicine must be used within a specific amount of time to ensure its effectiveness. The Ventolin HFA with an incorporated dose counter must be discarded 6 months after the pouch is opened, even if the dose counter does not yet read “000.” Symbicort HFA must be discarded 3 months after opening, even if not all the 120 doses it contains have been all used up.