Patches, injections and inhalers Flashcards
What is transdermal drug delivery?
where the drug is delivered (over time) using a patch on the skin
How is TDD achieved? (2 ways)
- by a matrix e.g. durogesic patches
2. using a rate limiting membrane (reservoir system) e.g. Scopaderm
How does the packaging of patches for TDD allow them to work?
- the patch is protected by an occlusive backing layer
- the adhesive creates a diffusion gradient and adheres to the skin
- a removable strip protects the adhesive
- in membrane systems, the membrane will be behind the adhesive layer
How are TDD patches packaged?
in a foil lined sachet like pouch for protection
In what form will the drug be in in the matrix/reservoir?
-the drug will be in solution/suspension
What are the advantages of TDD?
- by passes the GIT
- systemic effects
- no first pass metabolism (goes directly into systemic circulation)
- controlled constant rate of delivery
- long duration of action (up to 7 days)
What are the disadvantages of TDD?
- can cause skin irritation
- patch may fall off
- not suitable for all drugs (needs to be hydrophobic)
- not suitable for hairy areas
What formulations are injections in?
solutions, suspensions, emulsions
What are the different routes for injection?
IM, IV (bolus vs infusion), SC, intradermal, intraarterial, intraspinal
If a drug has low solubility, what is it formulated as?
Emulsions
Which of IV/IM are o/w and which is w/o?
IV is o/w whereas IM is w/o
What other excipients are needed for injection?
- Water - must be free of pyrogens (harmful bacteria) and be pure
- Preservatives - to prevent bacterial growth
- Buffers
- Tonicity adjusting agents e.g. 0.9% NaCl
In order of most to least, which formulations are the most stable?
emulsions — suspensions — solution
How are injections packaged?
- If as single dose ampoules, they’re in glass packaging,
- For multi dose vials, they’re in glass with a rubber bung
- Pre-filled syringes are in plastic/glass
- Can be given as infusion bags
What are the advantages of injections?
- they can be for local or systemic action
- used when oral route isn’t appropriate
- avoids all problems of the GIT
- no first pass metabolism
- rapid onset of action or prolonged release
What are the disadvantages of injections?
- they’re invasive/painful
- patients can be scared of needles
- risk of infection or embolism (block of an artery by a clot)
- difficult to reverse effects
- difficult to administer in some patients
How is particle size in inhalers related to drug penetration?
The smaller the particle size, the further down the respiratory tract the drug will penetrate
What is optimum particle size in inhalers and what happens above and below this size?
3-5 micrometers is optimum.
When they are less than 1 micrometer, the particles are exhaled and so the drug isn’t retained.
More than 10 micrometers results in particles staying in the oropharynx
What is an MDI?
They are aerosols of drugs in solution or suspension which have a propellant such as HFAs or CFCs
What does actuation result in in MDIs?
It results in evaporation of propellant to form droplets to be inhaled into the lung
What is the technique used by the patient for MDIs?
Coordination is required between actuation and inspiration as well as a long steady inspiration (to avoid exhaling the drug particulates)
What item can be used to aid the use of MDIs and how do they work?
Spacers are used to remove the need to coordination. Children are always prescribed a spacer with an MDI
What is a breath actuated MDI?
Inhalation triggers the actuation of the device and so this is used for those who have difficulty coordinating. Brands are easi breathe and autohaler
However a strong breath is required to trigger the actuation.
What are the excipients for MDI?
- Propellant (HFA and CFC)
- surfactants (to aid wetting for suspension e.g. oleic acid)
- co-solvents (to aid dissolution e.g. ethanol)
What is a dry powder inhaler?
This is breath actuated too but the drug is a micronised powder for inhalation. Brands include accuhaler, tubrohaler.
No propellant or coordination are required and larger doses are given.
What are the excipients in DPI?
- carrier for the drug e.g. accuhaler, lactose
- pure drug e.g. turbohaler
Which is more stable, MDIs or DPI?
MDIs are more stable as the container/packaging protects it from oxidation, hydrolysis and microorganisms. DPI however are susceptible to moisture degradation, therefore are less stable
What are the advantages of inhalers?
- can use small doses
- reduced systemic side effects
- fast onset of action
- can use drugs with poor bioavailabilty
What are the disadvantages of inhalers?
- difficult technique
- not suitable for all drugs
- only 20% of drug reaches the lung
- inflammation can reduce the size of the airways