Asthma pressurised metered dose inhaler performance: propellant effect studies in delivery systems

Area of Science:

• Pharmacology
• Respiratory Medicine
• Inhalation Therapy

Background:

• Current pressurised metered dose inhaler (pMDI) propellants, such as hydrofluoroalkane 134a (norflurane), are not pharmacologically inert like previous chlorofluorocarbons (CFCs).
• Inhaled propellants may exert smooth muscle relaxant effects and anaesthetic properties.
• Propellant gas volumes per actuation have not been previously quantified.

Purpose of the Study:

• To measure the volume of propellant gas released per actuation from pMDIs.
• To assess the impact of pMDI actuations on oxygen (O2) levels in valved holding chambers (VHCs) and lung ventilator devices.

Main Methods:

• In-vitro studies were conducted to measure gas volumes from pMDIs.
• Oxygen (O2) levels were monitored in VHCs and lung ventilator delivery devices following pMDI actuation.

Main Results:

• Propellant gas volumes varied from 7 ml to 20.4 ml per actuation depending on the pMDI type (HFA or CFC) and size.
• Total gas volumes ranged from 1640 ml to 3885 ml per inhaler.
• Oxygen levels in a VHC decreased to 11% after 10 actuations of a large HFA salbutamol inhaler.
• Ventilator devices showed a reduction in oxygen levels from 100% to 81-93% after five actuations.

Conclusions:

• Pressurised inhaler propellants have measurable gas volumes and can significantly reduce oxygen concentrations.
• Further investigation into the pharmacological effects, specifically smooth muscle relaxation, of these propellants is warranted.