PH2107 - Nebulisers Flashcards
What is a nebuliser?
A device which transforms a solution or suspension of medication into aerosol that is optimal for deposition into the lower airway
How many doses are delivered by a nebuliser?
One, over multiple breaths
What is the difference between a nebuliser and a pMDI and a Respimat Soft Mist inhaler?
A pMDI and a Respimat Soft Mist inhaler have dose metering capability
What are nebulisers driven by?
Compressed gas or oxygen, or by ultrasonically vibrating crystals
What are nebulisers used for?
When high doses of reliever medication are required
- emergency rooms
- ambulances
What are the advantages of using nebulisers?
- many patients can’t master the correct use of metered dose inhalers or dry powder inhalers (elderly and young children)
- some prefer the nebuliser over other aerosol generating devices
- possible to deliver virtually any drug and in virtually any dose, usually the first choice device during early phase clinical trials
What formulations can be used with a nebuliser?
- aqueous solutions
- suspensions
Describe aqueous systems used in nebulisers
- well established excipients in low concetrations
- dilute with 0.9% NaCl to adjust tonicity
- acids or bases to adjust pH
- need to be isotonic
- unit dose ampoules now standard
Give examples of suspensions that can be used with nebulisers
Drugs with low water solubility
- glucocorticosteroids
- micronized particles
- nanoparticles
Give two examples of types of nebuliser
- air jet
- electronic
How does an air jet nebuliser work?
Compressed gas is used to drive drug formulation through a spray nozzle
Describe the features of an air jet nebuliser
Traditional
- constant output - same output rate during inhalation and exhalation
- more than 50% dose unavailable to patient
Breath-enhanced
- quantity of aerosol generated during inhalation increased by control of air flow through device
Interval
- only generated aerosol during inhalation
How does an electronic nebuliser work?
Creates aerosols from ultrasonic vibration
Describe the features of an electronic nebuliser
Ultrasonic nebulisers
- aerosol formed from fountain above a vibrating piezoelectric crystal
Vibrating membrane nebulisers
- aerosol formed by extrusion of drug solution via a vibrating membrane, mesh or grid
Adaptive aerosol delivery
- aerosol delivery matches individual breathing patterns
What are the features of nebulisers?
- Several minutes to aerosolise a single dose
- Compressed gas causes evaporation and cooling
- temperature of solution falls
- nebuliser solution becomes concentrated - End of nebulisation marked by sputtering
- Device is not empty after nebulisation
- dead volume may comprise more than half the dose
What are the advantages of air jet nebulisers?
- relatively inexpensive
- simple formulation of drugs (including biotechnology products). Suspensions, emulsions, liposomes, other micro-particulates are also feasible
- well accepted (especially in hospitals and for infants)
- drug input can be halted at any time during dosing
What are the disadvantages of air jet nebulisers?
- dose to lung not readily controlled
- lengthy nebulisation time - compliance?
- large drug loss (up to 50% of starting volume left in nebuliser)
- large variability in nebuliser performance
- designed primarily for aqueous solutions (suspensions may show greater variability)
- evaporative cooling and concentration (drug precipitates)
- aerosol may be released into the atmosphere (contamination?)
- not highly portable
- noisy
What are the features of electronic nebulisers?
Compared to air jet nebulisers
- similar dead volume of liquid
- broadly similar output characteristics (model dependent)
- usually quieter and more compact than air jet nebuliser
Temperature of nebuliser fluid tends to rise
- potential damage to thermally sensitive compounds
Do not atomise suspensions and viscous solution efficiently
What are the features of vibrating membrane nebulisers?
Droplets formed at the membrane are small enough for delivery direct to the patient - no baffles needed - no recycle of liquid within the device - low dead volumes (< 1ml) - more efficient aerosol delivery - short nebulisation time Relatively compact, portable and energy efficient Battery operated
What is a DPI?
Dry Powder Inhaler
What are the features of a Pressurised Metered Dose Inhaler?
- portable
- convenient
- multidose
What are the limitations of a pMDI?
- difficult to co-ordinate
- requires propellant
- dose < 1mg per actuation
What are the opportunities for Dry Powder Inhalers?
- mostly breath-actuated (passive devices)
- propellant free
- higher doses than pMDIs
What size particles are in a DPI formulation?
Drug particles < 5um required
- BUT micronised drug particles highly cohesive
