Controlled Release Systems - Implants & Depot Injections

Question 1

What are the benefits of a controlled release system?

Answer 1

1. Frequency of drug administration is lowered
2. Different medicinal routes developed - e.g. parenteral, subcutaneous
3. Drug plasma concentrations can be measured at any time point
4. Desired drug levels can be maintained for a longer period of time

Question 2

What is zero-order drug release?

Answer 2

It is the steady state concentration of a drug on a graph, without any fluctuations.
This is the most desirable form of release.

Question 3

What are the 2 types of implants?

Answer 3

1. Biodegradable - implants are surgically implanted in the body, where the drug is released for a long time. This also minimises side effects.
2. Non-biodegradable - implants must be taken out once the drug is released

Question 4

How can the delivery rate of an implant be modulated?

Answer 4

By varying its polymer composition.

Question 5

Why do non-biodegradable implants achieve better controlled releases than biodegradable implants?

Answer 5

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

Question 6

What are the limitations of using a non-biodegradable implants?

Answer 6

1. Patient discomfort
2. Tissue fibrosis
3. Irritations

Question 7

What are some advantages & disadvantages of biodegradable implants?

Answer 7

Advantages:

1. Effective
2. Flexibility in drug type
3. Need only insertion & not removal

Disadvantages:

1. Patient discomfort
2. Requires insertion

Question 8

What 3 types of polymers can induce the release of a drug from an implant?

Answer 8

1. Polymer membrane permeation-controlled systems - drug must be permeated before its release, e.g. ocusert or ozurdex
2. Osmotic pressure-activated controlled systems - osmotic pressure controls drugs release, e.g. alzet
3. Hydrolysis-activated controlled systems - polymer undergoes hydrolysis & releases the drug, e.g. zoladex

Question 9

Why can solubility of a drug delay the release of it?

Answer 9

Because the drug would need to solubilise first before taking effect.
Solubility would be the rate limiting step here.

Question 10

What is the ocusert implant used for, and how is its use localised in its target region?

Answer 10

It is used for glaucoma. To facilitate its localisation in the eye, it contains a white titanium dioxide ring.

Question 11

What is the drug in ocusert sandwiched between?

Answer 11

The active ingredient (pilocarpine) is sandwiched between 2 non-biodegradable rate controlling membranes.

Question 12

How long is ocusert used for?

Answer 12

4-7 days

Question 13

What drug does ozurdex controllably release, and what is it used for?

Answer 13

Ozurdex is a polymer that releases dexamethasone in patients with diabetic macular edema (DMA) - diabetic retinopathy at the back of the eye.

Question 14

How is ozurdex administrated, and how long should it be given?

Answer 14

Via injection, which is needed every 3-4months.

Question 15

How long does it take for ozurdex to release its active ingredient?

Answer 15

4 weeks

Question 16

Why is iluvien preferred more than ozurdex for DME?

Answer 16

Because it is cost effective, as only 1 injection is needed which lasts 3 years.

Question 17

What do therapeutic contact lenses strongly depend on, in terms of acting as a reservoir for drugs?

Answer 17

1. Thickness of the lens
2. Molecular weight of the drug
3. Concentration of the drug loaded

Question 18

What is nexplanon used for, and what does it consist of?

Answer 18

It is used for up to 3 years of contraception.

It consists of a non-biodegradable polymer with 68mg of etonogestrel

Question 19

How much drug is released /day with the nexplanon implant?

Answer 19

60-70 ug of etonogestrel /day

Question 20

What is mirena (IUS) used for, and what hormone is present in it?

Answer 20

It is used for contraception for 5 years, and contains 52 mcg of levonorgestrel

Question 21

How much drug is released /day with the mirena implant?

Answer 21

20ug of levonorgestrel /day.

Question 22

Why does the mirena implant contain barium sulphate?

Answer 22

To allow us to see the device in x-ray examinations

Question 23

How does an osmotic pump, such as alzet, work?

Answer 23

1. A flexible bag contains the drug & a salt sleeve to form osmotic pressure
2. Water from the surrounding tissues diffuses through the implants permeable membrane
3. The drug is forced out of the implants reservoir from a flow moderator

Question 24

What is zoladex used for and what type of controlled delivery system is it?

Answer 24

It is a biodegradable controlled drug delivery system used to treat prostate/breast cancer.

Question 25

How long does the zoladex implant release its drug for?

Answer 25

3 months.

Question 26

What is a depot injection?

Answer 26

It is a type of slow release injection which uses a liquid to release the drug slowly into the system.

Question 27

What are leuprorelin depot injections used for?

Answer 27

It is used as treatment for prostate cancer & endometriosis

Question 28

What is risperdal consta used for, and where is it injected to in the body?

Answer 28

It is used for schizophrenia & other psychotic conditions.

It is injected into the deep intramuscular region (IM)

Question 29

What is the process of preparing a risperdal consta injection, using its vial/syringe?

Answer 29

1. The liquid from the ampoule is injected into the vial
2. This makes the liquid diluted to form a suspension
3. The liquid is then up-taken by the syringe, ready to be injected

Question 30

Which 2 HIV drugs are given via depot injections, and when during the patients treatment is it given?

Answer 30

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.

Question 31

What is the rate-limiting step of cabotegravir depot injections?

Answer 31

The dissolution of the drug particles into the surrounding intestinal fluid (solubility)