D4 Targeting different parts of the digestive system Flashcards
state 7 reasons that we coat tablets
- protection from environmental factors
- mask taste
- ease of swallowing
- mask batch wise colour differences
- easy identification by colour
- additional mechanical strength
- control drug release
what environmental factors may tablets need to be coated in order to be protected from?
light
moisture
why may a coating be needed to mask batch wise colour differences of tablets?
- different identical batches could have different colour tinges which can be masked with coatings to make sure they all look identical and adherence is maintained
- patients may panic if their tablets look an unfamiliar colour and they won’t take them
why may tablets need coating for mechanical strength?
prevents them crumbling or breaking if they are rattling around in a pot being carrier around
what are the 3 broad categories of tablet coating?
film coating
sugar coating
compression coating
what are the 3 different subdivisions of film coatings of tablets?
modified release
enteric release
immediate release
what are enteric coats used to do?
to prevent the tablets disintegrating (and the drug subsequently dissolving) in the stomach
what reasons may a drug need an enteric coating on its tablet?
- stomach acid ‘damages’ the drug
- drug ‘damages’ the stomach
how are film coatings applied to tablets?
thin film sprayed onto the tablet on a rotated, mixed tablet bed
what types of formulations can be film coated?
tablets
capsules
pessaries
granules
what are the typical constituents of film coatings for tablets?
- polymer (5-10%)
- vehicle / solvent (90%)
- plasticiser
- pigments
why is there a drying process in the steps for film coating tablets?
removes the solvent and leaves the film coat on the tablet
what additional thing happens when film coating granules as opposed to tablets?
granules are sprayed with film coating and circular drum rolls them around so they become fully coated
state polymers that are used for film coating
cellulose
cellulose ethers
cellulose acetate phthalate (CAP)
other non-cellulose derivatives
describe cellulose as a polymer used in film coating
- polymers used in film coating are often derivatives of cellulose
- often derived from natural products
- polymer of beta glucose
what is done to the hydroxyl groups of cellulose when it is used as a polymer for film coating and why?
hydroxyl groups are etherified to prepare polymers that are better suited to film coating
describe the use of cellulose ethers as polymers for film coatings
- approx half of the OH groups are methylated in methyl cellulose
- water solubility of polymer is improved by modifying
describe CAP (cellulose acetate phthalate) as a polymer used in film coating
- enteric film coatings are intended to be stable in the strongly acidic stomach environment
- CAP is a pH-sensitive cellulose derivative
which molecules are more soluble in water, free acids or their salts?
salts
what does the carboxylic acid group in CAP allow for when it is used as a polymer in film coating?
- available as an aqueous dispersion eliminating the need for organic solvents
- carboxylic acid group gives potential for ionisation in basic environment
ingredients of a typical enteric coating mixture
- cellulose acetate phthalate (5.0%)
- glyceryl triacetate (1.0%)
- isopropyl alcohol (17.0%)
- dichloromethane (68.5%)
- water (8.5%)
why is acetate a common ingredient in film coatings?
increases solubility
why should enteric coated tablets not be chewed or crushed?
- this would damage the enteric coat and the drug will dissolve in the gastric fluid
- this means it would have been released early
why do some tablets contain enteric coated pellets instead of enteric coating all around them?
stomach does not empty completely for around 4 hours so if the pellets are released, they will be allowed to pass through the pyloric sphincter faster because they are smaller
what type of medicines is it not a good idea to take with enteric coated medicines?
- antacids
- rise in pH of gastric fluid means enteric coat may dissolve in stomach
describe gastric emptying
- stomach only empties its contents periodically
- this allows time for digestion to commence
- small particles can pass through the pyloric sphincter but large intact tablets can’t
what does the purloin sphincter do when closed?
separates the stomach and duodenum
describe enteric coated granules with an example
- granules in omeprazole capsule formulations are EC
- the gelatin capsule shell dissolves in the stomach but the EC on the granules doesn’t
- the granules pass through the pyloric sphincter due to being smaller without the stomach emptying
what does MUPS stand for?
multiple unit pellet system
describe MUPS
- EC particles compressed into a tablet
- polymer coat needs to be flexible because of compression forces in tableting process
which polymers seem to be best suited to the EC of particles in MUPS tablets?
methacrylic acid copolymers
what principle do MUPS tablets work on?
- the same as EC granules in a capsule
- tablet disintegrates in the stomach and small EC particles can pass through the pyloric sphincter
