In metered-dose inhalers aerosol is generated with the aid of propellants like chlorofluorocarbons (CFC) or hydrofluoralkanes (HFA). They have a high dose consistency and average particle size as well as fine particle fraction are independent of the inspiratory air flow.

Mainly drugs in metered-dose inhalers are suspended within the propellant. They need to be shaken before use and generate particles with an average size of 3-5 µm. Substances insolution do not require shaking and are released from the inhaler with considerably smaller average size of about 1 µm thus being more easily deposited in the distal lung areas.

In most metered-dose inhalers aerosol inhalation has to be coordinated with dose actuation. Several studies have demonstrated that up to 70% of patients fail to complete the correct inhalation manoeuvre. This problem is overcome by breath-actuation or inhalation aids like spacers and holding chambers, which contrawise are more bulky to carry.



This section contains a list of things you should do (DOs) and things you shouldn’t do (DON’Ts) when using the pMDI. This list only covers items known from practice to be the most important and most likely to be forgotten or performed incorrectly by patients; this information is in addition to the prescribing and other information provided with the pMDI.

uso_si DO
uso_no DON’T
  • Take the cap off
  • Shake the inhaler
  • Seal lips around mouthpiece while opening the teeth
  • Start to breathe in slowly through the mouth
  • Then activate inhaler while continuing to breathe in
  • Breathe in slowly, over at least 5 seconds until lungs are full
  • Hold your breath as long as you comfortably can, then relax
  • Replace the cap
  • Check the dose counter on your inhaler regularly (if it has one) so you know when to get a new one in good time
  • Always keep a spare inhaler
  • Breathe in too quickly
  • Activate the inhaler before you start breathing in
  • Stop breathing in when you activate the inhaler
  • Stop breathing when you feel the medicine in your mouth
 © ADMIT, June 2009