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This page describes products and general use; it is not medical advice.
Short answer: a pressurized metered-dose inhaler (MDI) is built from a metal canister that holds the medicine, a plastic actuator that sprays it, a mouthpiece cap and, on some products, a dose counter. The canister and actuator are a matched set: the manufacturer’s instructions for use (IFU) for the product described here say not to swap either one with parts from another inhaler.
Who uses this reference: clinic and pharmacy staff who receive or reconcile inhaler stock, buyers who read product labeling, and students learning device anatomy. After reading, you should be able to name each part, say which parts belong together, and know what to check on the package and IFU.
What the parts of an inhaler are
The component names below come from the IFU for one FDA-approved product, Beclomethasone Dipropionate HFA Inhalation Aerosol (Amneal, IFU revision 07/2020). Other MDIs may be laid out differently, so each product’s own IFU is the authority for that product.
| Part | What the IFU says |
|---|---|
| Metal canister | One of the “2 main parts”; it holds the medicine. |
| Plastic actuator | The other main part; it sprays the medicine from the canister. The mouthpiece is part of the actuator. |
| Cap | Covers the mouthpiece of the actuator to protect it from dust. |
| Dose counter | Located on the back of the actuator; its window shows the number of actuations (puffs) remaining, starting at 120 on this product. |
How the parts fit together: a matched set
The canister sits in the actuator, and the two are supplied together. This IFU states that the canister must not be removed from the actuator, that its canister must not be used with an actuator from any other inhaler (including another inhaler of the same drug), and that its actuator must not be used with a canister from any other inhaler. For staff, the practical consequence is that a loose canister or a loose actuator is not a usable unit.
The dose counter
On this product the counter is “permanently inserted into the actuator” and “cannot be reset.” The counter shows the number of actuations remaining, so it is the label-defined readout for the device, not an estimate to be adjusted. The IFU also tells users never to change the counter’s numbers.
FDA addressed counters for oral MDIs in the guidance Integration of Dose-Counting Mechanisms into MDI Drug Products (final, CDER, issued March 2003, docket FDA-2003-D-0285). The guidance is intended for manufacturers developing oral-inhalation MDIs; it is not specifically intended for MDIs for other routes such as nasal MDIs, and it is not intended for multidose dry powder inhalers, which FDA notes already incorporate dose counters.
MDI versus dry powder inhaler parts
The parts above describe a pressurized MDI. A dry powder inhaler is a different design with different components. For the design differences, see MDI vs DPI. Two related pages cover accessories and a separate device class: the valved holding chamber (a holding chamber used with an MDI) and the nebulizer.
What staff should check on the package and IFU
- The canister and actuator are the pair supplied together; the IFU forbids mixing parts between inhalers.
- The cap is present, since its stated job is to keep dust off the mouthpiece.
- The dose counter window is readable and shows the count the IFU describes for a new unit (120 for the product above).
- The expiration date on the package is present and not passed.
- The IFU in the box is the one for that exact product. To trace a device record, see Basic UDI-DI; for sourcing questions see gray market medical supplies.
Common mistakes
- Treating parts as interchangeable. The IFU says not to pair a canister with another inhaler’s actuator, or the reverse.
- Taking the canister out of the actuator. The IFU says not to.
- Expecting to reset the counter. It cannot be reset and the numbers are not to be changed.
- Washing the device in water. For this product the IFU says not to wash or put any part in water. Other products may differ, so read that product’s IFU.
FAQ
What are the main parts of an inhaler?
For the metered-dose inhaler described in the Amneal IFU: a metal canister that holds the medicine and a plastic actuator that sprays it, plus a cap over the mouthpiece and a dose counter on the back of the actuator.
Can I use a canister from one inhaler in another actuator?
No. The IFU for this product says not to use its canister with an actuator from any other inhaler, nor its actuator with a canister from any other inhaler.
Can the dose counter be reset?
Not on this product: the IFU says it cannot be reset and is permanently inserted into the actuator.
Sources
- Amneal, Instructions for Use: Beclomethasone Dipropionate HFA Inhalation Aerosol, revision 07/2020 (FDA-approved product), https://products.amneal.com/beclo/wp-content/uploads/sites/12/2026/04/Beclo-dipro-HFA-Inhalation-IFU-Rev-07-2020-01.pdf. Checked 2026-11-01. Facts above apply to this product.
- U.S. FDA, Integration of Dose-Counting Mechanisms into MDI Drug Products (guidance, March 2003, final), https://www.fda.gov/regulatory-information/search-fda-guidance-documents/integration-dose-counting-mechanisms-mdi-drug-products. Checked 2026-11-01.
