Drug Delivery Devices Flashcards
What is an MDI?
Metered Dose Inhalers (MDI)
- Contains Bronchodilator drugs
- Solution mixed with CFC propellant
- Environmentally friendly HFC propellant
- When bannister is pressed fixed volume of drug released
What does canister mechanism lead to?
Rapid Vaporisation of propellant breaks drug up the liquid stream into an aerosol for inhalation
What volume is in each metered dose?
between 25 and 100 micro litres
What % reaches lungs?
10%
What % reaches mouth/throat?
80%
Where does drug deposited in mouth throat?
- Absorbed in blood via mucus
- Swallowed
What about the remaining drug go?
Exhaled air or left in apparatus
What is key for efficacy of drug delivery?
Inhaler technique
Advantages of MDI’s?
- Portable and Compact
- Treatment time is short
Disadvantages of MDI’s?
- Complex hand/breathing co-ordination is required
- Drug concentrations are fixed
- Possible reaction to propellant
- High oropharyngeal impaction loss
Common Inhaler errors?
- Dust cap not removed
- MDI not held upright
- Canister not shaken to disperse drug
- Firing of MDI not coordinated with breath in
- Breath in too fast
- No breath hold
- Aerosol released onto tongue/teeth
- Canister is empty
How can extensions on MDI’s help?
- They decrease particle size and velocity before inhalation
2 main types of extensions?
- Volume Holding devices
- Spacer devices
Describe Volume holding devices
- Cone Shaped Extension chambers
- Aerosol spray cloud
- Volume 750cm^3
- Also aerochamber which is smaller
How do you use a Volume Holding device?
1) Insert the MDI into end of the device
2) Shake the cone/drug beforehand
3) Put lips around mouthepiece
4) Breathe all the way out
5) Press canister once and breathes in slowly and deeply via mouth
6) Hold breath for 10s
7) Breathe normally again on mouthpiece and hold breath for as long as comfy and then relax
8) Wait at least a minute before repeating 2-6
Describe spacer device?
- 10 cm tube
- Vol 100cm3
- Open end for inhalation
Spacer technique
Same as above but breathe out gently OFF the device and then lips tight on deep breathing and breath hold 10s
-Wait 1 minute and repeat
What are the advantages of extension devices?
- Oropharyngeal deposition is reduced
- This is bc larger particles deposit on walls of attachment
- This decreases side effects
- Improved Drug delivery from 10 increasing to 14-20%
- Less need for good technique
What are DPI’s?
Dry Powder Inhalers
How does a DPI work?
- They overcome technique/coordination issues
- Drug is a powder in a small MDI
- Powder dispensed during inspiration
- Breath activated
Example of DPI?
Rotadisk and Turbohaler
Advantages of DPI’s?
- Small and Portable
- Short Preparation and time
- Decreased coordination requirements
- Dose counter available
Disadvantages of DPI’s?
- Limited range of drugs available
- Poss reaction to carrier e.g. glucose/lactose
- Increased inspiratory flow rates required
- Some require loading beforehand
Why do we use Nebulisers?
- Severe airway obstruction
- Deliver higher dose than MDI’s/DPI’s
- All nebulisers contain a reservoir to hold liquid drug
Commonly used nebulisers?
- Jet nebuliser
- Ultrasonic nebuliser
Should a mouthpiece or facemask be used?
- Lung deposition is same in adults/older children with either
- Depends on patients choice
- Facemasks better for infants
When would a mouthpiece be recommended?
- Cortricosteroids or anticholinergics are nebuliser use a MP due to potential problems with glaucoma or raising IOP
What does MMAD stand for?
Mass Median Aerodynamic Diameter
How does a nebuliser work?
(1) [Compressed Gas]
- Uses compressed gas which passes rapidly through a narrow opening creating an area of low pressure
How does a nebuliser work?
(2) [Gas Flow rate]
-Gas flow rate used to nebulise particles to 2-5mm (small airway deposition)
How does a nebuliser work?
(3) [Liquid in reservoir]
- The liquid in reservoir pushes upwards by atmospheric pressure and gets atomised
How does a nebuliser work?
(4) [Droplets/baffle]
-Liquid gets shattered into droplets by baffle system and aerosol produced for inspiration
What is the Venturi effect?
Venturi = restriction in a tube
- Varies flow rate of gas/liquid
- Pressure falls and gas velocity increases
- Forces liquid up (Bernoulli)
What gas sources could be used?
- Oxygen (beware if inc PaCO2)
- Air cylinder
- Wall Mounted outlets
How does flow rate affect delivery?
- Affects treatment time and size of particle produced
- Aerosol size is inversely proportional to gas flow rate
Good flow rate?
- flow rate of 6-8 l/min ensures a MMAD of < 5um
How does fill volume affect delivery?
Increasing fill volume increases delivery time
What is important with equipment?
CLEAN IT!
-Often single patient use
REVISE CALCULATIONS?
Approximately how many actuations of a salbutamol inhaler (100ug) are equivalent to administering 2.5 and 5mg of salbutamol via a nebuliser?
When would a nebuliser be necessary?
- When large doses are needed
- Controlled coordinated breathing is difficult
- Hand held inhalers ineffective
Advantages of Nebs?
- Aerolize any drug solution
- Minimal co-ordination needed
- Effective with low inspiratory flows
- Drug conc can be modified
- Higher doses
Disadvantages of Nebs?
- Expensive and big
- Lengthy treatment times
- Dose delivery inefficient and wasteful
- Contamination of equipment possible
- Higher dose may lead to more Side effects
How does fill volume effect nebs?
- Increased FV leads to longer time delivering
- Increased nebuliser time may mean patient less likely to want to use
- BD’s usually in pre-packaged ampoules
Tapping effect?
Tapping increases volume output of the nebuliser
