How to Know If Your Asthma Inhaler Is Empty

A boy using an inhaler outside
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You may think the answer to this question is easy — that a person knows when their inhaler is empty when it stops spraying. But this answer is actually wrong. 

A Common Misconception

HFA-based metered-dose inhalers (MDIs) utilize a propellant to deliver the medication, and the propellant will continue to spray long after the medication has run out. Therefore, it is possible to continue to use an asthma inhaler while inhaling only propellant and no medicine. Obviously, this can present a major concern, especially when it comes to rescue inhalers used for the emergency treatment of asthma symptoms.

For people taking the new HFA-based metered-dose inhalers (MDIs), knowing when the inhaler is empty or close to being empty can be a challenge. The currently available albuterol inhalers, with the exception of Ventolin HFA, do not have a dose-counter on the inhaler. In addition, most of the steroid-containing inhalers, such as QVAR, Symbicort, and Advair HFA, also don’t have dose-counters, although Flovent HFA does.

A Simple Calculation

Since the steroid-containing inhalers are used routinely, it is possible to determine when the inhaler is empty:

  • First, determine the number of inhalations contained in the asthma inhaler when it is new from the pharmacy (this number should be clearly printed on the box, or you can ask your pharmacist). For most steroid-inhalers, this number is 120.
  • Next, determine how many puffs you use every day from your inhaler. In many cases, people use two puffs twice a day or four puffs a day. Realize that the number of puffs used daily may vary depending on what your doctor has prescribed.

Then, the number of days that your inhaler will last is:

The number of inhalations that the inhaler contains divided by the number of inhalations you use daily.

For example, Advair HFA contains 120 inhalations. The usual amount prescribed of this medication is two puffs twice a day, or four total puffs every day. 120 divided by 4 is equal to 30. Therefore, an Advair HFA device should last 30 days.

A Word From Verywell

I often recommend to my patients to make the above determination when they start a new inhaler and/or new dosing regimen. When they obtain their new inhaler, I recommend writing the “empty date” on the inhaler with a Sharpie marker. For example, if a new inhaler is started on October 1, then write October 31 on the inhaler. This will remind you to get a new inhaler on October 31, whether or not the old inhaler continues to spray propellant.

Unfortunately, the above rule doesn’t apply to albuterol (rescue) inhalers, since most people don’t use this medication on any regular basis. In addition, the new HFA-inhalers don’t work to “float” the device in a bowl of water, an old trick that worked to determine how full the old CFC-based inhalers were. Instead, I often recommend to my patients that once their albuterol seems to be less-than-half-full when they shake it, they should get a new one.

Of course, the makers of Ventolin HFA love to point out that their device contains a dose-counter, which eliminates all of the guess-work and uncertainty about how much medicine is left in an inhaler. My suspicion is that other manufacturers of albuterol will soon follow suit, as it only makes sense to know that there’s medicine available for you to use when you need it most — when an asthma attack is occurring.

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  1. Sander N, Fusco-Walkert SJ, Harder JM, Chipps BE. Dose counting and the use of pressurized metered-dose inhalers: running on empty. Ann Allergy Asthma Immunol. 2006 Jul;97(1):34-8. doi: 10.1016/s1081-1206(10)61366-x