release Flashcards
What is drug release?
The process by which a drug leaves a formulation and is subjected to absorption.
What is rate of release controlled by?
Physiochemical properties of the delivery system.
Why is drug release modified?
To achieve optimal concentration levels of drug in plasma, where the drug is effective but not toxic.
What is delayed release? give an example.
Delayed release is the release of drug after a lapse of time, or after environmental conditions are reached.
Example is enteric coating.
What is repeat action release?
A delivery system where doses of drug is released at different times.
What is prolonged release?
Where drug is released slowly to maintain plasma conc over time. There are two types being;
- sustained: long duration but constant
- controlled: constant rate of release then sustained at optimal levels.
How can polymer be used to modify drug release?
- Enteric coating: breaks down in higher pH to protect the drug from the environment or vice versa, or to target an area.
- Matrix tablet and embed a drug: a large complex that can manipulated as desired.
- Targeted delivery: adhesion and release locally.
Describe the mechanism and use of enteric coatings.
Enteric coatings are made of pH sensitive polymers that are resistant to hastric pH and dissolve when exposed to intestinal pH. This can be used to protect the drug from the stomach enivronment, environment from the drug, or target areas of the GI system.
Describe the mechanism and use of matrices for release
Used for sustained release, where this involves penetration of surrounding liquid, dissolution of drug in penetrated liquid and leaching of drug through interstital channels or pores.
These processes causes release to be much slower.
Describe release from a non-erodible polymer.
Here, water will enter the matrix and dissolve drug which diffuses out. This creates a depletion zone that the solvent will need to cross in order to reach and dissolve more drug, resulting in an inconsistent plasma concentration of drug.
Describe release from an erodible polymer.
Eroding matrices means that there is no depletion zone as the matrix will erode as drug is dissolved. This gives essentially consistent release.
Describe the osmotic pump system
This is a form of controlled release, where release is perfectly consistent.
Water enters the osmogen through the semi-permeable polymer membrane, causing it to expand and push drug out of the drug reservoir via the delivery oriface.
Describe the use and mechanism of bioadhesive polymers.
These are coatings that bind biological surfaces, where an example is mucoadhesion.
Heres, drug will bind to mucous membrane al allows for interaction at a localised area, increasing contact time with the target tissue.
This can be used for potential optimal drug absorption or action on a local disease..
Describe the use and mechanism of ion-exchange resins.
This uses polymer beads of 1-2mm that bind to charged drug molecules.
This allows charged drugs to have optimal properties,
What is the Higuchi equation and what does it assume?
Q = K(H) x t^1/2
It assumes that intial drug concentration is higher than the solubility of the drug, diffusion only occurs in one dimension, matrix does not erode and diffusion coefficient is constant, and perfect sink conditions are obtained.
Quantifies drug release rate.
