D4. Targeting different parts of the digestive system Flashcards
Why coat tablets?
-Protection from environmental factors
e.g. light, moisture…
-Mask a bitter/unpleasant drug taste
-Substances need to be in solution to be tasted
-Ease of swallowing
-Coatings can mask batchwise differences in tablet colour
-Coatings may be coloured allowing easy identification
-May confer additional mechanical strength
-To control when (and for how long) a drug is released
types of tablet coating?
-film coating
-sugar coating
-compression coating
Describe film coating
-immediate release
-modified release
-This category includes enteric release coating
Describe enteric coats
Enteric coats are used to prevent the tablet disintegrating (and the drug subsequently dissolving) in the stomach, because of either:
-Stomach acid “damages” the drug
-Drug “damages” the stomach
How is film coating done?
-Thin film sprayed onto the tablet on a rotated, mixed tablet bed
-Capsules, pessaries, granules and others may also be coated
-Drying process removes the solvent and leaves the film coat on the tablet
What are the typical constituents in film coating?
-Polymer (5 - 10%)
-Vehicle / solvent (90%)
-Plasticiser
-Pigments
what polymers are used for film coating?
-Polymers used in film coating are often derivatives of cellulose
-Hydroxyl (– OH) groups of cellulose are etherified to prepare polymers that are better suited to film coating
ONE NOTE
Describe Cellulose acetate phthalate (CAP)
-Enteric film coatings are intended to be stable in the strongly acidic stomach environment
-CAP is a pH-sensitive cellulose derivative
-Henderson-Hasselbalch
ONE NOTE
What polymers are used for enteric coating?
-Other (non-cellulose derivate) polymers are also used in enteric coating
-Methacrylic acid copolymers
-Like CAP contains an acidic functional group
-Available as an aqueous dispersion eliminating the need for organic solvents
ONE NOTE
Typical enteric coating?
ONE NOTE
Describe gastric emptying
-The stomach only empties its contents periodically – allows time for digestion to commence
-Small particles can pass through the pyloric sphincter (separates the stomach and duodenum) but large intact tablets cannot
Describe enteric coated granules
-The granules present inomeprazole capsuleformulations are ec
-Although the gelatin capsule shell dissolves in the stomach the enteric coat on the granules does not
-Being much smaller than a typical tablet / capsule the granules can pass through the pyloric sphincter without the stomach emptying
Describe MUPS
-MUPS = multiple unit pellet system
-Enteric coated particles compressedinto a tablet
-The polymer coat needs to be moreflexible because of the compression forces that are applied in the tableting process
-Methacrylic acid copolymers seem to be best suited to the enteric coating of particles making up MUPS tablets
-MUPS tablets work on the same principle as ec granules in a capsule, i.e. tablet disintegrates in the stomach and small ec particles can pass through the pyloric sphincter
