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AAI: Pharmaceutics > Delivery Systems & Formulation For Inhalation > Flashcards

Delivery Systems & Formulation For Inhalation Flashcards

1
Q

How do we deliver drugs to the lungs?

A

Aerosol

Dispersion of solid particles or liquid droplets in a gas

(Needs a source of energy required to form an aerosol)

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2
Q

Types of inhalers

A

1) Nebulisers
2) Pressurised metered dose inhalers (pMDI) - widely used + most convienient
3) Dry powder Inhalers (DPI)

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3
Q

Nebulisers

A

Aqueous drug solution/suspension aerolised onto droplets

  • energy provided by compressed air or ultrasound
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4
Q

pMDI

A

Drug formulated in a liquefied gas under pressure

  • Aerosol formed by evaporation of the gas at atmospheric pressure
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5
Q

DPI

A

Drug normally with other solid excipients in a dry powder state

  • Aerosolisation by patient’s inhalation
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6
Q

2 types of Nebulisers

A

Jet Nebuliser

Ultrasonic Nebuliser

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7
Q

Jet Nebuliser

A

Air from a compressor forced through a narrow hole to give high velocity air stream

  • High velocity air breaks drug solution/suspension into droplets for inhalation
  • baffles used to remove larger particles
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8
Q

Ultrasonic Nebuliser

A
  • Piezoelectric (vibrating) crystal emits high frequency signal
  • breaks drug solution/suspension into droplets for inhalation
  • lighter + quieter than a jet nebuliser
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9
Q

How to use nebulisers

A

Patient breaths normally into face mask/mouthpiece

Patient needs to wash it every time

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10
Q

Advantages of Nebulisers

A
  • aqueous drug solutions
  • no hand-lung coordination
    • good for elderly + children
  • no controlled inhalation manoeuvre required
    • useful in severe, acute asthma attacks
  • large doses of drugs not normally available can be given
  • low cost
  • visible mist (patient reassured)
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11
Q

Disadvantages of nebulisers

A
  • not fully portable
  • equipment not fully regulated
  • lengthy nebulisation time
  • low efficiency
    • as low as 10% of drug reaches lungs
  • solution concentrates as water evaporates
  • insoluble drugs require solubilisation
  • some suspensions can be difficult to nebulise
  • susceptible to microbiological contamination
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12
Q

Name the different parts of a MDI

A
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13
Q

Metered dose inhaler (Canister) container requirements

A

Must:

  • withstand high pressure
  • Robust
  • Light in weight
  • Inert
  • Made of aluminium/stainless steel
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14
Q

pMDI metering valve

A

Ensures accurate + reproducible volume of drug formulation is delivered

Different from continuous spray valves

volume = 25-100 microlitres

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15
Q

pMDI propellant requirements

A

Must be:

  • liquid under pressure
  • gas at atmospheric pressure + ambient temperature
  • that its vapour pressure must stay constant
  • non-flammable, non-toxic
  • chemically inert + compatible with drug formulation
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16
Q

Types of propellants in pMDIs

A

Chlorofluorocarbons

Hydrofluoroalkanes

17
Q

CFCs

A

Ozone depleting gases

Banned

Responsible for ‘cold-freon effect’

18
Q

Hydrofluoroalkanes

A

Drugs need to be re-formulated due to different properties of HFA vs CFC

New valve materials had to be developed

19
Q

What is the dose range for each actuation in a pMDI?

A

Dose per actuation from 5 microgram to 5 milligram

20
Q

Drug formulation types for pMDIs

A

Drug is soluble in propellant

  • drug solubilised in propellant
  • ethanol might be added as a co-solvent

Drug is insoluble in propellant (most common)

  • micronised drug particles suspended in propellant
  • surfactants added to increase suspension stability
21
Q

Suspension formulation of a pMDI

A
  • each volume of suspension must be homogenous
  • surfactants added to formulation to
    • improve stability
    • aid in the formulation of a flocculated suspension
  • surfactants approved in inhaled products: oleic acid, sorbitan trioleate, lechitin
22
Q

Problems with suspensions

A

Sedimentation

Flocculation (reversible aggregation by shaking)

Caking (difficult to redisperse)

Particle size growth by Ostwald ripening (deposition in lungs reduce)

23
Q

How can we minimise caking

A

Controlled flocculation

24
Q

what is the ideal suspension stability

A

Slow flocculation (>30 secs)

Slow sedimentation (>30 secs)

Easy redispersion

(still need to shake device before use to redisperse settled flocculates)

25
Q

Excipients included in pMDI drug formulation

A

Flavours - to mask bitter drugs

Sweeteners - to mask bitter drugs

Lubricant - to improve valve operation

Density modifiers - to decrease sedimentation rate

Antioxidants - to prevent chemical degradation

26
Q

Why use spacer devices with pMDI

A

Increase lung deposition

  • delay between actuation + inhalation
  • decrease velocity of the spray
  • more time for the propellant to evaporate

However, it is cumbersome (have to carry around bulky device) + decreases dose inhaled by patient (deposition in the device as electrostatic charges cause droplets to stick to chamber)

27
Q

How to improve inhalation of pMDI

A

Spacer devices

Breath-actuated pMDI

28
Q

Why does a Breath-actuated pMDI improve inhalation for the patient?

A

Inhaler is fired by the patients inhalation

No coordination needed

Particles still leave inhaler at a high velocity

29
Q

Advantages of pMDI

A

Compact, portable, robust, convenient

Multi-dose

Short treatment time

Consistent format

Good dose content uniformity

Inexpensive

Good protection against moisture + pathogen

Inexpensive

30
Q

Disadvantages of pMDI

A

Usually no breath-actuation

Low lung depostion

No dose counter

Only low doses can be delivered (<1mg)

Need priming before use

Performance depends on temperature

Drug formulation is challenging

Not environmentally friendly - HFAs are still greenhouse gases

31
Q

What are Dry Powder Inhalers?

A

Delivers dry powder, no solvent

Developed for delivery of sodium cromoglicate as large dose could not be delivered by pMDI

Breath actuated (no coordination required)

As a drug + excipients in a dry form tend to be more stable than drug dispersed in a solvent as in pMDI

32
Q

Components of DPI

A

Drug powder or blend of drug with excipients

Drug reservoirs or pre-metered doses

Body of device

Cap to protect powder from dust, moisture

33
Q

Principles of DPI operation

A

Patient’s inspiration flow is used to:

  • fluidise the static powder blend
  • de-aggregate particle agglomerates into inhalable particles

Dose delivered + deposited into the lungs depends on the patient’s inspiratory flow rate

34
Q

DPI - particle de-aggregation

A

Particles less than 5 micrometers are extremely cohesive

35
Q

Types of DPI

A

Unit dose device

Multiple unit dose

Reservoir devices

36
Q

DPI: Single uni dose device

A

Drug excipients In capsule

37
Q

DPI: multi-unit dose

A

.

38
Q

DPI- multidose reservoir devices

A

.

AAI: Pharmaceutics (7 decks)

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