Pressurised Metered dose Inhalers Flashcards
pMDI - lecture
what are pMDIs?
- compact, pressurised aerosol dispenser for oral inhalation - multiple doses (200) of finely dispersed drug to the lungs.
- needed for treatment of asthma - only fraction of drug reaches the deep lungs.
- pMDIs are either suspension formulations or solution formulations.
Formulation types
suspension formulations = consist of micronised drug particles suspended in propellant. challenges include agglomeration, caking and particle growth, clogging of valves and powders and propellant must be dry.
Solution formulations = offer better deep lung deposition, with reduced oropharyngeal deposition.
Components
Propellant = hydrofluoroalkanes (HFAs) are common due to environmental safety and stability.
Surfactants and Co-solvents = maintain uniform suspensions and stabilise formulations.
E.g.) salbutamol sulphate and beclometasone dipropionate.
Device features
- Valves control dose delivery and spray characteristics
- Metering valves ensure accurate dosing
- Containers are typically made of aluminium, tin plate, glass, or plastic - chosen for durability and compatibility.
Particle delivery
- Aerodynamic diameter determines the effectiveness of drug delivery.
- Cascade impactors are used to measure particle size distribution and inhalation performance.
Manufacturing and Filling
2 methods: cold filling and pressure filling, with quality checks like leak tests and spray tests.
Challenges and Innovations
- new strategies include the use of advanced surfactants and particle engineering for better performance and stability
Raoul’s Law and Dalton’s law
- used to calculate vapour pressure in propellant blends.
cascade impactor
- used to characterise aerodynamic particle size.
- for unit density spherical particles
K = CρUDp2 /18µDc - Where:
- U = Relative Velocity of the air flow, ρ = Particle
Density, Dp = Particle Diameter - µ = Gas Viscosity, Dc = Diameter of the Orifice Jet,
C = Cunningham Slip-Correction Factor
