Lecture 17 - implants Flashcards
what are types of implants ?
contraceptive implants
drug coated orthopaedic implants
polymer coated drug eluding stents
intravitreal implants
what are the material characteristics of implants ?
in crystalline solid suspension, the polymer phase is amorphous, the drug phase is amorphous and the appearance is opaque.
in amorphous solid dispersion, the polymer phase is amorphous the drug phase is amorphous and the appearance is transparent
in amorphous solid solution he polymer phase is amorphous the drug phase is amorphous and the appearance is transparent
what are delivery considerations for implants?
Implants deliver a fixed dose in a fixed volume, which is not adjustable based on individual patient weight (mg/kg) or body surface area (mg/mm²).
Functional lifetime is controlled by the total drug in the implant reservoir (volume ~2 ml) and delivery rate controlled by the implant
Maximum delivery dose generally limited to ~1 g
If treatment needs to be stopped, the implant can be surgically removed
what are excipients used in biodegradable implants
Poly(lactide-co-glycolic acid) – PLGA
Poly(lactic acid) – PLA
Collagen
describe glidel wafers
he Gliadel wafer is specifically used for local treatment of brain cancer
Brain cancer has a very poor prognosis, with survival typically ranging from 3 to 12 months after diagnosis.
The recurrence of glioma, the cancerous tumor, usually happens only at the site of the primary tumor.
The treatment approach with the Gliadel wafer requires a surface-eroding (biodegradable) polymer to deliver the therapy directly to the tumor site.
An antitumor agent with a very short half-life is needed in this treatment to minimize neurotoxicity
how is glide wafer drug released
Upon degradation, the anhydride bonds in the polymer are hydrolyzed to yield two products: carboxyphenoxy propane and sebacic acid.
the products are renewals secreted and sebacic acid metabolised in the liver
The release of carmustine, the active anticancer drug in the wafer, is controlled by the degradation of the polymer matrix.
discuss a contraceptive implant
The implant is rod-shaped, designed for 3 years of birth control, and it releases the hormone etonogestrel.
It is made from ethylene vinyl-acetate (EVA) copolymer and contains 68 mg of etonogestrel.
The core of the implant has a higher concentration of vinyl acetate (28%), making it a highly viscous liquid similar to glue, while the skin has a lower concentration (15%), making it more film-like.
The drug is released through diffusion out of the core but does not pass through the outer skin of the implant, which allows for strong control of the release kinetics.
describe in situ gelling injectables
In-situ gelling injectables provide prolonged drug release and are easy to administer, potentially allowing for patient self-administration.
They pose a reduced risk of dose dumping (uncontrolled release of the drug) due to impact, storage, and transport conditions.
Production costs for these injectables are lower compared to implants.
They have the potential to carry a higher drug load
The formulations are solutions at room temperature (RT) and before injection.
Gelling occurs in response to physical stimuli such as temperature changes (using materials like chitosan/β-glycerophosphate and poloxamers), pH changes (using materials like Carbopol 934), and changes in ion concentration (using materials like pectin, sodium alginate, and gellan gum).
A novel approach involves the use of supramolecular gelator molecules which can form gels upon certain stimuli.
