Inhalation systems | Features of available devices | pMDI - Press. Meterdose Inhaler

Characteristics of pressurized metered-dose inhalers (pMDI)

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 in solution 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.

Literature:

Voshaar T. Therapie mit Aerosolen. 2005. Uni-Med: Bremen

Course of particles using a pressurized metered dose inhaler (pMDI)

Description
This animated model shows the aerosol flow generated by a pressurized metered dose inhaler into the upper respiratory tract.

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