Types of Inhalers

In general, the two big categories of inhalers are metered dose inhalers (MDI) and dry powder inhalers (DPI).

Metered dose inhalers (MDIs) are pressurized containers with medicine in aerosol form. The most common propellant used is usually Hydrofluoroalkane, or HFA. MDI requires patients to click/actuate and then immediately take a slow, deep breath. This can be problematic for patients with difficulty coordinating breathing and actuation. The use of a spacer can help with delivery of the medication. Spacer holds the medicine in the chamber, and patients can then take breath in without having to worry about the exact timing. Another type of MDI called Respimat uses soft mist without propellant. This mitigates the need to use a spacer. Downside is that there is an extra step with twisting the inhaler prior to use and may require more education.

Dry powder inhalers (DPI) deliver medication without a propellant. This requires the patient to take in a fast, forceful breath. There are many types of DPIs. Some require patients to insert a capsule, others will require only push a button or pull back a lever. Patients will need to be able to have sufficient inhalation force. This can be prolematic for patients with poor lung functions to start with.

Often times, a hand held inspiratory flow device can be used to measure whether a patient has enough inspiratory force to use a particular MDI or DPI. One example of this device is the In-Check Dial G16. As a general rule, a patient needs to be able to have peak inspiratory flow rate of at least 60 L/min to be able to use dry powder devices. He or she needs to be able to have at least 30 L/min peak inspiratory flow to be able to use metered dose inhalers.^{1, 2}

A simplified resistance profile of commonly used inhalers are seen above. When in doubt, pick the device with the lowest resistance. A more detailed table of different examples of inhalers is as below:

Inhaler Type	Image	Characteristics	Upsides	Downsides
HFA inhalers		Most common type of MDIs	Most common, easier to learn	Requires good hand-breath coordination. Spacer can help with delivery
Redihaler		Delivery is activated with inhalation instead of actuation	Does not require click or press. Bottom chamber acts as spacer.	Patient still needs to take slow, deep breath
Respimat		Uses soft mist instead of propellant	Delivers slower soft mist. Better delivery. Does not need spacer	More steps. Patient has to turn the base and then press a dose release buttton
Diskus		Most common type of DPI. Patient opens cover until it clicks. Then medicine is delivered with inhalation	-	-
Ellipta		Another very common type of DPI. Works like a Diskus	-	-
Handihaler		Single use DPI that requires capsule for each use	-	Requires capsules to be placed each time prior to use
Twisthaler		An example of DPI that uses twisting motion to deliver	-	-
Flexhaler		An example of DPI that uses twisting motion to deliver	-	-
Pressair		DPI device that uses pushing down of a button to deliver	-	-
Inhub		DPI device that works similar to a Diskus	-	-
Respiclick		Delivers when cap is clicked back	No washing, priming, shaking. No hand-breath coordination	Hard to be approved by insurance