Pressurised Metered Dose Inhalers + Nebulisers Flashcards
What must the drug be in pMDI?
Dissolved/suspended in non-polar volatile propellant
Describe the delivery of the drug in pMDI
Drug in solution or suspension in pressurised canister
Actuation of metering valve - pre-determined dose released
Vol expansion of formulation
Enters airways as fine spray of droplets
What does deposition depend on?
Inspiratory flow + separation
What are the containers?
Aluminium canisters
10-30ml
Inert
What is the vol of medicine in the metering valve component?
25-100 microL
Describe the metering valve component
Inverted position
Valve stem fits into actuator
Describe what happens with metering valve component
Depression of valve stem = contents discharged
After actuation = refills with liquid
What must happen to pMDI?
Needs to be primed
= pressed multiple times
Describe the actuator component
Polyethylene or polypropylene
What do the dimensions of the orifice in the actuator determine?
Shape, speed + emitted aerosol
Describe the propellants component
Liquefied gases
Liquid under high pressure in cannister
What are the propellants that are used?
Hydrofluroalkanes
What are the problems with propellants?
Poor solvents
What can pMDIs be?
Solution or suspension
What should the particle size be?
Solution or suspension
Why does it say to “breathe in slowly + deeply”?
Minimise inertial impaction
Why does it say to “hold your breath for as long as possible”?
Allow for drug particle to follow air into lungs
Why does it say, “do not breathe into the inhaler”?
Block the valve
Why does it say to “shake”?
If the formulation is a suspension
What do spacers reduce?
Aerosol velocity, allowing for more time to inhale the drug
What must you make sure when dispensing a spacer?
Compatible with pMDI mouthpiece
What may be attached to a spacer for young patients?
Mask
What is the drug in nebuliser?
Dissolved/suspended in polar solvent (usually H2O) + aerosolised
How does nebuliser deliver it to the lungs?
Drug in solution/suspension added to nebuliser drug reservoir
Nebuliser connected to power source
Drug solution aerosolised
Enters airways as fine spray of droplets
What is dissolution dependent on?
Droplet density, charge + size
What is absorption dependent on?
Patient inhalation pattern + airways
What are the different types of nebulisers?
Jet nebulisers
Ultrasonic nebulisers
Vibrating mesh nebulisers
What do nebulisers consist of?
Compressor supplying compressed air
Nebulising chamber containing nebulised drug
Mouthpiece or face mask
What are jet nebulisers driven by?
Driven by compressed air
What does the rate of air flow determine in jet nebulisers?
Droplet size + rate of drug delivery
Describe the Bernoulli principle + Venturi effect
Compressed gas passes through capillary tube
= increases air velocity = low pressure zone around nozzle (V)
= formulation to rise in liquid reservoir (B)
What are the issues with jet nebulisers?
Quite noisy = affect patient acceptability
Continuous operation = significant amount of drug lost
Describe how ultrasonic nebulisers work
Sound wave created from vibration of piezoelectric crystals at high frequency
= creates crests that break liquid particles into small droplets
What do ultrasonic nebulisers require?
Power source
How do vibrating mesh nebulisers work?
Passing liquid drug through vibrating mesh
What droplet size do vibrating mesh nebulisers produce + what is it ideal for?
1-5 micrometres
Ideal for deep lung deposition
What are the advantages of vibrating mesh nebulisers?
Quieter + more portable
Describe formulating nebuliser fluids
Formulated in H2O
Surfactants added = suspension
Iso-osmotic fluid = pH3-10
What isn’t often added to nebuliser fluids + why?
Antioxidants + preservatives = cause bronchospasm
Why must it be pH 3-10?
Avoid bronchoconstriction
What is poorly delivered from ultrasonic nebulisers?
Suspensions
Why may the fluid in jet nebuliser drop in temperature?
Due to evaporation of solvent during nebulisation
What may happen if the fluid drops in temperature?
Drug solubility may be reduced
Affect asthmatic patients who suffer from bronchoconstriction
