Inhaler devices for asthma treatment
In this entry (part 1 of 2), I would like to review basic devices for delivering asthma medications. Proper administration of asthma medications for the best results can be helped not only by using proper technique, but also understanding a little background on how they work. I review the basics of the three main drug delivery devices:
- Metered dose inhalers (MDIs)
- Dry powder inhalers (DPIs)
Next month, in part 2, I will review devices that help optimize delivery of inhaled medications to the lungs from metered dose inhalers, including spacers/holding chambers, and some other newer features of inhalers to help patients take care of their asthma.
Metered dose inhalers (MDI)
The metered dose inhaler is the oldest type of asthma inhaler. There are two main components:
- The canister holds the medicine under pressure (usually a very fine suspension of a powder), which, when activated, sprays medicine from the point of delivery (the stem).
- The dosing chamber (also called the ‘boot'), into which the canister inserts, receives the dose of medicine and disperses it into a fine spray which is breathed in by the patient.
Due to the fact that the medicine in an MDI is under pressure, it comes out of the inhaler as a relatively fast-moving jet that slows down as it gets further away from the mouthpiece. Due to this and the size of droplets that are generated by the inhaler, most medication from an inhaler doesn't make its way to the lungs -- most of it is deposited in the mouth, throat, and above the voicebox before it can get into the lungs. In fact, even with the best inhaler technique, only a quarter of the dose sprayed from a metered dose inhaler ends up in the lungs. Not to worry, this is well known by MDI manufacturers and the dose that comes out of the inhaler is calculated for what will end up in the lungs.
Proper technique is very important for keeping down the fraction of medication that ends up in the mouth/throat. Your doctor, nurse, or respiratory therapist should take you through the proper steps in good inhaler technique, especially if you have not used and inhaler before or feel that you are not getting relief from your inhalers (this applies particularly to quick relief inhalers (bronchodilators)).
Dry Powder Inhalers (DPI)
Dry power inhalers differ from metered dose inhalers in two main ways:
1) the patient breathes in, both bringing the medicine out of the device and into the lungs, so there is no need for the patient to time their breath with medicine delivery as in an MDI
2) while the patient is supposed to breathe in slowly with and MDI, he or she is supposed to breathe in quickly with a DPI. Another subtle feature about DPIs is that the size of particles is a little smaller, so a slightly larger fraction of medication that is breathed in gets into the lungs. Overall, there are several advantages of DPIs. However, they are not the best choice for individuals whose breathing is weak, since the force of taking a deep breath in is what brings the medication out of the device and into the patient's lungs.