Controlled Release Systems - Implants & Depot Injections Flashcards
What are the benefits of a controlled release system?
- Frequency of drug administration is lowered
- Different medicinal routes developed - e.g. parenteral, subcutaneous
- Drug plasma concentrations can be measured at any time point
- Desired drug levels can be maintained for a longer period of time
What is zero-order drug release?
It is the steady state concentration of a drug on a graph, without any fluctuations.
This is the most desirable form of release.
What are the 2 types of implants?
- Biodegradable - implants are surgically implanted in the body, where the drug is released for a long time. This also minimises side effects.
- Non-biodegradable - implants must be taken out once the drug is released
How can the delivery rate of an implant be modulated?
By varying its polymer composition.
Why do non-biodegradable implants achieve better controlled releases than biodegradable implants?
Because the shell of the non-biodegradable implants is going to stay intact, so the drug will be diffused in a controlled manner (achieving zero-order kinetics) - desirable
What are the limitations of using a non-biodegradable implants?
- Patient discomfort
- Tissue fibrosis
- Irritations
What are some advantages & disadvantages of biodegradable implants?
Advantages:
- Effective
- Flexibility in drug type
- Need only insertion & not removal
Disadvantages:
- Patient discomfort
- Requires insertion
What 3 types of polymers can induce the release of a drug from an implant?
- Polymer membrane permeation-controlled systems - drug must be permeated before its release, e.g. ocusert or ozurdex
- Osmotic pressure-activated controlled systems - osmotic pressure controls drugs release, e.g. alzet
- Hydrolysis-activated controlled systems - polymer undergoes hydrolysis & releases the drug, e.g. zoladex
Why can solubility of a drug delay the release of it?
Because the drug would need to solubilise first before taking effect.
Solubility would be the rate limiting step here.
What is the ocusert implant used for, and how is its use localised in its target region?
It is used for glaucoma. To facilitate its localisation in the eye, it contains a white titanium dioxide ring.
What is the drug in ocusert sandwiched between?
The active ingredient (pilocarpine) is sandwiched between 2 non-biodegradable rate controlling membranes.
How long is ocusert used for?
4-7 days
What drug does ozurdex controllably release, and what is it used for?
Ozurdex is a polymer that releases dexamethasone in patients with diabetic macular edema (DMA) - diabetic retinopathy at the back of the eye.
How is ozurdex administrated, and how long should it be given?
Via injection, which is needed every 3-4months.
How long does it take for ozurdex to release its active ingredient?
4 weeks
Why is iluvien preferred more than ozurdex for DME?
Because it is cost effective, as only 1 injection is needed which lasts 3 years.
What do therapeutic contact lenses strongly depend on, in terms of acting as a reservoir for drugs?
- Thickness of the lens
- Molecular weight of the drug
- Concentration of the drug loaded
What is nexplanon used for, and what does it consist of?
It is used for up to 3 years of contraception.
It consists of a non-biodegradable polymer with 68mg of etonogestrel
How much drug is released /day with the nexplanon implant?
60-70 ug of etonogestrel /day
What is mirena (IUS) used for, and what hormone is present in it?
It is used for contraception for 5 years, and contains 52 mcg of levonorgestrel
How much drug is released /day with the mirena implant?
20ug of levonorgestrel /day.
Why does the mirena implant contain barium sulphate?
To allow us to see the device in x-ray examinations
How does an osmotic pump, such as alzet, work?
- A flexible bag contains the drug & a salt sleeve to form osmotic pressure
- Water from the surrounding tissues diffuses through the implants permeable membrane
- The drug is forced out of the implants reservoir from a flow moderator
What is zoladex used for and what type of controlled delivery system is it?
It is a biodegradable controlled drug delivery system used to treat prostate/breast cancer.
How long does the zoladex implant release its drug for?
3 months.
What is a depot injection?
It is a type of slow release injection which uses a liquid to release the drug slowly into the system.
What are leuprorelin depot injections used for?
It is used as treatment for prostate cancer & endometriosis
What is risperdal consta used for, and where is it injected to in the body?
It is used for schizophrenia & other psychotic conditions.
It is injected into the deep intramuscular region (IM)
What is the process of preparing a risperdal consta injection, using its vial/syringe?
- The liquid from the ampoule is injected into the vial
- This makes the liquid diluted to form a suspension
- The liquid is then up-taken by the syringe, ready to be injected
Which 2 HIV drugs are given via depot injections, and when during the patients treatment is it given?
Cabotegravir & rilpivirine.
They are both given as 2 separate injections every 2 months after an initial oral lead-in period.
The patient must have an undetectable viral load.
What is the rate-limiting step of cabotegravir depot injections?
The dissolution of the drug particles into the surrounding intestinal fluid (solubility)
