Controlled Release Systems Flashcards
What are the benefits of controlled release systems?
achieve desired drug level in plasma for a prolonged time period
- drug plasma concentrations are predictable
- the frequency of drug administration is lower than a conventional dosage form
- it is possible to achieve a zero order drug release
What are the types of implants/inserts?
they can be solids or semisolids being either biodegradable or non-biodegradable
What are the advantages and disadvantages of erodible inserts/implants?
advantages
- effective
- flexibility in drug type and dissolution rate
- need only insertion not removal
disadvantages
- patient discomfort
- requires insertion
What are the advantages and disadvantages of non-erodible inserts/implants?
advantages
- controlled rate of release
- prolonged delivery
- flexibility for type of drug selected
- sustained release
disadvantages
- patient discomfort
- irritation to eye
- tissue fibrosis
What are the types of controlled release systems?
polymer membrane permeation controlled systems
- ocusert, ozurdex
osmotic pressure activated controlled systems
- alzet
hydrolysis activated controlled systems
- zoladex
How does ocusert work?
polymer membrane permeation controlled system
- made as an ocular implant
pilocarpine (drug) is present in a reservoir as drug-alginate complex
- microporous ethylene vinyl acetate copolymer used is rate controlling
release of drug occurs via diffusion of drug through pores in the semipermeable membrane
it also contains a white titanium dioxide ring to localise the drug in the eye
- prevents spread of drug to other systems
How does ozurdex work?
polymer membrane permeation controlled system
- made as an ocular implant
is a polymer (PLGA) coated pellet that release dexamethasone drug in the vitreous humour of patients with diabetic macular oedema
- is biodegradable
implant releases drug as polylactide co-glycolide (PGLA) hydrolyses to lactic acid and glycolic acid which are then removed by further metabolism
What is Iluvien?
an intravitreal implant containing corticosteroid
- fluocinolone acetonide
Why are contact lenses used for drug delivery? What types are used? What does their use depend on?
provides extended release of drug into the eye
hydrogel soft contact lenses can be used to absorb drugs and release them into the post lens lachrymal fluid
- minimises clearance and sorption through the conjunctiva
use depends on the ability of the contact lenses to be a drug reservoir
- depends on water content and thickness of the lens
- depends on the molecular weight of the drug and the concentration of the drug loaded
What is a nexplanon implant?
a contraceptive implant that can be used unto 3 years
- is non-biodegradable solid
composed of ethylene vinyl acetate impregnated with etonogestrel as a solid dispersion in silicone matrix
What is a intrauterine system? What is an example?
hormonal contraceptive inserted into the uterus
Mirena
- levonorgestrel is present as a solid dispersion in a silicone matrix
= is released at a constant rate
How does alzet work?
osmotic pressure activated controlled system
- zero order release
the drug is in solution in a reservoir bag with a flexible impermeable wall
the reservoir is surrounded by another reservoir containing the osmotically active agent which is in turn surrounded by a semi permeable membrane
- upon insertion into the body, water from surrounding tissues penetrates through the semipermeable membrane dissolving the osmotically active agent thus increasing osmotic pressure
- this creates pressure on the collapsible drug reservoir reducing its volume and forcing the drug out of the reservoir through an orifice
What can affect release of drug in alzet?
osmotic pressure activated controlled system
water flow rate which can be affected by
- osmolality of the osmotic agent within the release unit
- permeability of the polymer membrane
How does zoladex work?
hydrolysis activated controlled systems
- is a biodegradable controlled drug system
it is a cylindrical subcutaneous (s.c) polylactide co-glycolide (PLGA) implant containing gosrelin
- the hydrolytic degradation of the polymer chains control the release of the drug
drug release is achieved initially by surface erosion of the polymer then bulk erosion
What is leuprorelin depot injection?
leuprorelin acetate is a gonadotropin releasing hormone agonist/analogue
- used to treat prostate cancer and endometriosis
- depot injection means its given either i.m or s.c
drug is incorporated into microspheres made of either PLGA or polylactic acid
