Non-degradable polymer implants and inserts Flashcards
What drug does Norplant release?
Levonorgestrel
Where is Norplant injected?
Subdermal
How many flexible closed capsules are there?
6
What is Norplant made of?
Dimethylsiloxane/Methylvinylsiloxane
What is the total quantity of drug in Retisert?
Fluocinolone acetonide 0.59mg
What is the initial rate of release of FA in Retisert?
0.6ug/day then decreasing over first month to steady state of 0.3ug-0.4ug/day
how long does retisert work for
30 months
indication of retisert
uveitis
Describe structure of retisert
FA core in silicone elastomer cup and PVA membrane positioned between drug core and orifice to control drug release. PVA suture tab anchors the implant inside the eye
Where is Iluvien injected
Injected into vitreous cavity in order to release FA to posterior segment of eye
Indication of iluvien
Reduce inflammation in diabetic macular oedema
Total quantity of drug in Iluvien
0.19mg of FA
How long does Iluvien work for
36 months
Describe the structure of ILuvien
- Internal matrix containing 0.19mg of FA
- Permeable membrane of PVA at one end through which drug is released
- Non-bioerodable tube of polyimide
- Non-permeable cap at the other end
What drug and quantity does Mirena release?
52mg of Levonorgestrel
What materials are used in Mirena?
Polydimethylsiloxane reservoir
BaSO4 which is radiopaque is included in some to enable tracking
How long is Mirena licensed for?
Contraception up to 5 years
4 years in endometrial protection
Name 3 MOA of Mirena
- Thickens cervical mucus to prevent sperm from entering uterus
- Thins uterine lining
- Inhibits sperm from reaching/fertilizing egg
Name 4 non-biodegradable reservoir systems?
- Norplant
- Iluvien
- Retisert
- Mirena
Why is it difficult to achieve zero order drug release in matrix/monolith devices?
Because of drug dispersion - drug near the surface will be released faster than drug in centre of device
In non-degradable matrix devices does drug release increase, decrease or remain the same over time and why?
Decrease as drug near the surface of matrix is depleted as drug diffusion progresses. Remaining drug has to travel further in order to be released.
what equation describes drug release from non-degradable polymer implants which are matrix devices?
M is proportional to square root of time
or M = k root t`
This is the Higuchi equation
explain drug release from matrix type non-degradable polymer implants
- Up to 60% of the total drug is released following the Higuchi equation.
- After 60%, release slows down exponentially as the remaining drug molecules are deep inside the matrix and must travel further to reach the surface.
- The implant remains non-swellable and non-dissolving, meaning its structure stays the same.
- The diffusion coefficient (D) remains constant.
What drug does Taxus DES release?
Paclitaxel
