How to Know If Your Asthma Inhaler Is Empty

You may think the answer to this question is easy—that a person knows when their inhaler is empty when it stops spraying.

Anxious boy using an inhaler outdoors
Seb Oliver / Getty Images

A Common Misconception

HFA-based metered-dose inhalers (MDIs) contain a propellant to deliver the medication that will continue to spray even 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 in the case of rescue inhalers that are used to treat asthma symptoms in an emergency.

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

Inhalers that contain steroids are used on a regular basis to prevent asthma symptoms from occurring: For this reason, they often are called "controller" inhalers. Since they typically are used a predetermined number of times per day (or week), it's possible to determine when the inhaler is empty in three simple steps:

  1. Note the number of inhalations contained in your 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.
  2. Consider the number of puffs you take every day from your inhaler. This will vary depending on the severity of your asthma and your healthcare provider's orders.
  3. Divide the number of inhalations in the device by the number of puffs you take each day. This will tell you how many days the medication will be available. For example, if your inhaler contains 120 inhalations and your healthcare provider has you take two puffs twice a day, that's a total of four puffs per day. One hundred twenty divided by four equals 30; therefore, your inhaler will last 30 days.

For some people with mild to moderate persistent asthma, the math may be a bit more complicated. According to updated recommendations about asthma treatment from the National Institutes of Health (NIH) issued in December 2020, individuals in this group may not need to use an inhaler every day to control their asthma. If this applies to you, talk to your healthcare provider about how the new guidelines might affect your treatment. If your prescription changes, you'll need to determine a different formula for calculating how long your inhaler will last.

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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