metered dose inhaler Flashcards
what is a pressurised meter dose inhaler?
compact, pressurized aerosol dispenser designed for oral inhalation delivery of multiple doses (200) of finely dispersed drug to the lungs. Valve volumes 25-100 ml.
emitted fine drug suspension is available for inhalation
what kind of deposition in the lungs is needed for asthma treatment?
deep lung deposition- not alveolar deposition which leads to systemic absorption instead of interaction with bronchioles.
what precentage of the dose reaches the lung area?
aprox 20%
what formulations do pMDIs come in?
either suspension formulations (majority) or solution formulations
how do you use a pMDI?
Shake the inhaler well before use Remove the cap Breathe out, away from your inhaler Bring the inhaler to your mouth. Place it in your mouth between your teeth andclose you mouth around it. Start to breathe in slowly. Press the top of you inhaler once and keep breathing inslowly until you have taken a full breath. Remove the inhaler from your mouth, and hold your breath for about 10 seconds, then breathe out.
what is the basic formulation of suspended particles?
100 mg per 100 ml = 0.1 % w/v
what is the propelllant and what is it used for?
propellant –‘heart’ of the system with high vapour pressure
what is the jobs of the surfactant and co-solvent?
surfactant –maintain uniform suspension and lubricate valve
co-solvent –improve solubility of surfactant. Usually ethanol up to 10% w/v
give an example of an oil soluble surfactant and what its HLB means?
oleic acid oil- has to have a low HLB of around 3 meaning that it is oil soluble
what size is the drug in the suspension formulation?
micronized (1-10 mm). ‘square-circular’ shape Problems due to agglomeration
what properties does a propellant have?
liquified gas •do not deplete ozone (CFCs banned) •non-flammable •suitable vapour pressure •non-toxic •use hydrofluoroalkanes(HFAs) •poor solvents for most drugs used for asthma, hence suspensions are formulated
what is tetrafluoroethane and what are its properties?
it is a propellant
it is relatively polar compared to CFCs
gives low molecular attraction
high vapour pressure
why do surfactants usually need a co-solvent?
usually not very soluble in HFA
what is the purpose of a surfactant?
stabilize suspension, adsorbing to particles to remove air, promote good wetting and flocculation
what happens upon actuation?
larger droplets (around 30 mm diameter) travelling at 30-50 m s-1undergo ‘flash vaporization’ •patient inhales drug with trace of surfactant. Ethanol should be driven off with propellant •if propellant hits back of throat –cough reflex known as ‘cold freoneffect’
what are the problems associated with suspension formulations?
caking •agglomeration •particle growth •clogging of valves •powders and propellant must be dry (<300ppm)
what is the difference in the two formulations?
greater deep lung deposition and lower oropharyngeal deposition compared to CFC suspension
what happens in solution process to delivery the drug?
droplets evaporate and patient inhales very fine particles of drug that were in solution.
true or false :solution not bioequivalent with respect to suspension, reduce dose
true
what are the types of new stratigies with no surfactants?
use hollow lipid porous particles –‘pulmospheres’ –match density of the formulation. Propellant permeates within the particle.(ii)suspended annealed particulate salbutamol sulphate in tetrafluoroethane
(iii)trapping HFA
what are more recent formulations?
Proventil, salbutamol sulphate (with ethanol/oleic acid) suspension in HFAFlovent, fluticasone propionate in HFA suspension. No surfactant or co-solvent used.Ventolin, salbutamol sulphate in HFA onlyAtrovent–ipratropium bromide solution with HFA, using co-solvent (water/ethanol) and surfactant (citric acid)
what is Oligolacticacids (OLAs)?
short chain polymers of lactic acid, better solubility (>5 %w/w) in HFAs
what do spray characteristics depend on?
the propellant system
what are the 4 main spray characteristics of aerosols?
vapour pressure of the propellants: higher pressure = greater disruptive forces = finer spray
•propellant-product ratio: the greater the proportion of propellant, the finer & drier the spray. Single propellant gives finer spray than a mixture of propellants with same vp
•presence of solvents: these lower vp
•Viscosity: as viscosity of formulation increases, droplet size increases and may give stream
what are the 3 other factors that influence spray characteristics of aerosols?
temperature: rapid change in vpwith temperature (non-linear increase). Most testing done at 21.1 oC, however may change for hotter overseas climates•valve design•actuator
what are the two functions of valves?
a device used to seal the aerosol container and permit a controlled discharge of the contents
how does a metering valve work?
This fills up, empties and fills up again- keeps taps opening and closing
There is a slight hole in stem oriphous
Allows liquid to flow.
