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3.24 > Lecture 8: Formulation of medicines for the respiratory system > Flashcards

Lecture 8: Formulation of medicines for the respiratory system Flashcards

1
Q

What are the Pulmonary delivery devices used to generate an aerosol?

A
  • Pressurised meter dose inhalers (pMDI)
  • Dry powder inhalers (DPIs)
  • Nebulisers
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2
Q

What are the most common active pharmaceutical ingredients delivered y aerosols?

A
  • b2 agonists
  • Anticholinergics
  • Corticosteroids
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3
Q

What is the definition of an aerosol?

A

Colloidal systems consisting of very finely subdivided liquid or solid particles dispersed in and surrounded by a gas

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4
Q

What is the definition of an aerosol?

A

Colloidal systems consisting of very finely subdivided liquid or solid particles dispersed in and surrounded by a gas

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5
Q

Define Mass median aerodynamic diameter (MMAD)

A

Diameter at which 50% of the particles of an aerosol by mass are larger and 50% are smaller than the median diameter

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6
Q

Define Fine Particle Fraction (FPF)

A

Fraction of particles (< 5 micron diameter) that can achieve deposition in the lower respiratory tract

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7
Q

Define labelled dose

A

Dose that is metered and stated on device packaging e.g. Flixotide® 125 (125mcg fluticasone per actuation of inhaler)

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8
Q

Define Emitted dose

A

The mass of drug emitted per actuation that is actually available for inhalation at the mouth

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9
Q

What are the advantages of local treatment of respiratory disease

A
  • Non-invasive and painless
  • Delivers high drug concentrations directly to the disease site(s)
  • Rapid clinical response
  • Bypasses barriers to therapeutic efficacy e.g. poor GI absorption, first-pass metabolism
  • Achieve similar or superior clinical effects with a fraction of a systemic dose e.g. 2 - 4mg salbutamol PO is equivalent to 100 – 200 mcg by pMDI
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10
Q

What are the disadvantages of local treatment of respiratory disease

A
  • Administration techniques differ between and within device categories
  • Less than optimal technique of device can therefore compromise therapeutic effect
  • More patient training and time is required for effective drug administration
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11
Q

What are the five key components of a metred dose inhaler?

A
  • Container
  • Propellants
  • Actuator
  • Metering valve
  • Formulation
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12
Q

What is the container of a metred dose inhaler made from and what are the advantages?

A

Aluminium
- Light
- Inexpensive
- Compact material

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13
Q

Why is the container of a metred dose inhaler made from alumium?

A

Prevents ingress of daylight (good for photostability)

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14
Q

Wha are the requirements of a container?

A

Must be able to withstand the high pressures generated by the propellant

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15
Q

What is the internal surface of a container of a metred dose inhaler coated with and why?

A

inert polymer to prevent interaction of the formulation with the container surface e.g. adhesion of drug particles in a suspension formulation

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16
Q

What is the actuator of a metred dose inhaler manufactured using?

A

plastic injection moulding techniques

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17
Q

What does the actuator house?

A

pMDI canister and has an inbuilt nozzle

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18
Q

What volume of the formulation does a metering valve deliver?

A

25 - 100 nL

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19
Q

What is the basic operating principle of metering valve?

A
  • Prior to activation a channel between the container body and the metering chamber is open to allow formulation entry into dosing chamber
  • As the pMDI is activated, this channel closes, and another channel connecting the metering chamber to the atmosphere opens
  • The pressurized formulation is expelled rapidly into the valve stem, which, together with the actuator expansion chamber allows the propellant to start to boil resulting in the production of an aerosol plume
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20
Q

How is the metering valve used?

A

The canister is used in the inverted position, with the valve below the container to allow valve filling under gravity
Some valves are surrounded by a retaining cup that contains a few doses of drug

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21
Q

What can impact upon aerosol particle size distribution and subsequent lung distribution?

A

The actuator polymer and the nozzle design

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22
Q

What is a pMDI?

A

A solution formulation where drug is dissolved in the propellant. Homogeneous phase so patients do not need to shake the inhaler immediately prior to use.

23
Q

Why are co-solvents or surfactants used in pMDI?

A

Drug solubility in HFA may be limited

24
Q

What surfactants are used in pMDI?

A
  • sorbitan trioleate
  • oleic acid
  • soya lecithin
  • typically at 0.1% to 2% w/w
25
Q

What co-solvents are used in pMDI?

A
  • Ethanol
  • Glycerol
  • Propylene glycol
26
Q

What are the effectds of ethanol?

A
  • Changing the formulation density and thus changing the total mass of formulation atomized during device actuation
  • Changing atomization of the formulation and the size of the atomized droplets
  • Changing the evaporation rate of the droplets towards their residual particle sizes
27
Q

What are the processes to reduce particle size?

A
  • Milling
  • Micronizing
28
Q

What is a principle consideration for a suspension?

A

The drug must be practically insoluble in the formulation vehicle

29
Q

What can facilitate a drug being insoluble in a formulation vehicle?

A

The use of an insoluble salt eg salbutamol sulfate, fluticasone propionate

30
Q

What can happen to particles in formulation?

A

May sediment or cream (rise) upon standing so need to shake to uniformly re-suspend particles before use and ensure uniform dosing

31
Q

What is sedimentation defined by?

A

Stokes law

32
Q

What are the particle interactions that change particle size distribution?

A
  • Mechanical interlocking due to surface asperities
  • Capillary forces from the presence of water
  • Electrostatic interactions
  • van der Waals forces
33
Q

What can minimise formulation issues with pMDI suspenstions?

A

The use of suspending agent stabilisers eg PEG 0.05 - 0.5% (w/w) with 0.001% (w/w) PVP to reduce inter-particle cohesiveness
and Surfactants (minimise electrostatic interactions)

34
Q

What is MMAD from suspension pMDI dependant on?

A

Aerosol droplet size and particle concentration

35
Q

Why is the interest in DPI increasing?

A
  • They are simpler to use and are breath activated
  • They are propellant-free and environmentally friendly
  • DPIs preferred for their stability and processing since they are formulated as one phase, solid-particle blends
36
Q

What are the four basic features all DPI have?

A
  • a dose-metering mechanism
  • an aerosolisation mechanism
  • a de-aggregation mechanism
  • an adaptor to direct the aerosol into the mouth.
37
Q

What are the two types of devices DPIs can be?

A

Single or multi unit devices

38
Q

What is the composition of DPI powder?

A

consist of micronised API (0.5 - 5 mm) supported on a coarse carrier e.g. lactose particles (~ 50–200 mm).

39
Q

What is the minimum threshold energy of a DPI?

A

Each DPI has a minimum threshold energy below which de-agglomeration is inefficient, resulting in a reduced emitted dose with a high MMAD and small FPD. Below the minimum threshold energy, the patient will receive no, or very little, therapeutic effect from the drug.

40
Q

What factors are DPI dose dependent on?

A
  • The properties of the drug formulation (powder flow, particle size, shape and surface properties, drug/ carrier interactions)
  • The performance of the inhaler device
  • Correcr inhalation technique for deposition in the lungs
  • Patient inspiratory flow rates
41
Q

What does a good API aerosolisation require?

A

Adhesive forces between API particle and the coarse carrier particle to be overcome

42
Q

What do lactose particles have?

A

Surface asperities which can prevent API not being fully exposed to flow stream preventing detachment

43
Q

What is done to enhance re-dispersion of API?

A

Fine lactose (<32 μm) is blended with larger lactose particles

44
Q

What is the active site theory?

A

Fine lactose particles occupy the high energy surface areas of the larger lactose carrier particle. This leaves only lower energy binding sites (less adhesion) on the surface for the API to occupy.

45
Q

Describe the dose uniformity of DPI?

A

Blended formulations of small API particles and large excipient carrier particles

46
Q

Wha can cause poor dose uniformity?

A

Mixing powders with different properties, particle sizes and ratios is technically challenging and if inadequate can cause poor dose uniformity

47
Q

What is a critical step in the manufature of a DPI

A

Blending

48
Q

What were the first devices developed for inhialation therapy?

A

Nebulisers

49
Q

What are the two common types of nebulisers?

A
  • Air-jet nebulisers
  • Vibration mesh nebulisers
50
Q

Describe air jet nebulisers

A
  • Traditional nebulizer type
    -U ses compressed air to generate a fine mist
  • Offers a range of particle sizes
  • Can be loud
  • No medication restrictions
  • Durable
  • Available in table top models and handheld models
51
Q

Describe vibrating mesh nebulisers

A
  • Newer nebuliser technology
  • Uses ultrasonic vibrations passed through water to generate a fine mist
  • Offers a very consistent particle size
  • Virtually Silent
  • Medication restrictions
    suspensions
    heat is transferred to the medication e.g. dornase alpha
  • Available in handheld models only
52
Q

What devices are used for inspiratort flow >30L/ Min in patients with Good actuation-inhalation coordination?

A
  • pMDI
  • BA-pMDI
  • DPI
  • Nebuliser
53
Q

What devices are used for inspiratort flow <30L/ Min in patients with Good actuation-inhalation coordination?

A
  • pMDI
  • Nebuliser
54
Q

What devices are used for inspiratort flow >30L/ Min in patients with poor actuation-inhalation coordination?

A
  • pMDI + spacer
  • BA-pMDI
  • DPI
  • Nebuliser

3.24 (28 decks)

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