Aerosols Flashcards
Advantages of pulmonary route
Direct lung targeting
Non invasive
Rapid onset of action
Avoid GI Tract
Large sa and blood supply for drug abs7
Most devices are portable
Disadvantages of pulmonary route
Correct technique of inhaler usage is important for efficient delivery
Disease state- increase volume of mucus in lung infections or compromised inhalation effort
Local/throat irritation possible
Stability of aerosols
Generally lower delivery efficiency
Anatomy of respiratory tract
Trachea
Bronchi
Alveolus
Airway diameter decreases and cross sectional area increases down this path
Site of deposition and its effects
Back of throat= swallowed
Bronchioles= for local treatment
Alveoli= systemic absorption
Aerodynamic diameter
Diameter of a sphere with unit density that has the same sedimentation rate in air
Factors that affect the aerodynamic size
(Higher) Density of particle
Unit density
(Higher) Physical diameter
Shape factor
Inertia impaction - deposition mechanism
Particle carried by a gas stream has its own momentum
Airstream changes direction/velocity so particle follows the changing airstream or follows its own momentum and impact on airways walls
What happens to particles > 5um
Deposit in the upper airways by inertia impaction as it has a high momentum
Sedimentation= deposition mechanism
Particles suspended in a fluid is subjected to vertical gravitational force
Particles between 1-5 um
Deposit in lower airways
Diffusion= deposition mechanism
Random movement of particles through a fluid (brown Ian motion)
Rate is inversely proportional to particle size
Particles less than 1um
What other factors affect particle deposition
Elongated particles have small aerodynamic diameters so easily deposit in alveoli
Porous or hollow particles have lower density = good aerodynamic properties
Hydrophilic particles pick up on the moisture and grow in size+ agglomerate and stay in upper airways
What can you tell, the patient to have optimal deposition
Deep breath to increase inhaled volume so there is an increased deposition at lower respiratory tract
Slow inspiration to reduce flow rate and reduce deposition at upper respiratory tract by inertial impaction
Breath holding to increase deposition by sedimentation and diffusion
Suspensions
Drug with low solubility
Some sprayed droplets will be drug free
Good chemical stability
High powder loading may clog spray exit
Drug caking/ flocculations may lead to dose variability
Solution
High drug solubility in propellant
Each sprayed particle contains drug
May need a co solvent to aid dissolution
Chemical stability may be a problem
Greater flexibility on adaptor design and finer sprayed particle size
No caking problem
Spacers
Improve delivery efficiency for children because it provides extra time for propellant drop,eat to evaporate which reduces particle size and reduce impaction in throat because smaller momentum
Reduce droplet velocity- reduce impaction and momentum
Coordination not required
Reduce cost of treatment
Disadvantages of using spacers
Bulky
Requires cleaning
Drug may be lost inside the spacer
Breath- actuated mdi
Drug release is triggered by inspiration so does not require coordination
Need a forceful breathe in which can be difficult
Advantages of Dry powder inhaler
Does not require propellants
Passive, no coordination required
Higher delivery efficiency
Higher dose can be given
Disadvantages of dry powder inhaler
Complex delivery system so higher cost of production
Different mechanisms
Energy input may not be sufficient to deaggregate powder
Advantages of nebulisation
Can be inhaled during normal tidal breathing
Useful for patients with difficulty using other inhalers (acute conditions, children, elderly)
Disadvantages of nebulisation
Need to be used with nebuliser which is bulky
Long administration time for high dose administration
Require cleaning= higher maintenance cost
Aerosol contamination to the environment
What is nebulisation
Delivery of large volumes/ doses of drug in the form of a mist inhaled into the lungs
Jet nebulisers
Jet of high velocity compressed gas passes through a nozzle, creating regions with reduced pressure
Ultrasonic nebuliser
Crystals generates ultrasonic frequency
Vibrating mesh nebuliser
Liquid passes through a vibrating mesh
Ultrasonic vibration
Soft mist inhaler
No propellants
