Green: Advanced Coating Flashcards
What is the purpose of coating tablets?
- Aesthetics: can hide the colours
- Mask taste: sweeteners
- Different release times: slow release to protect tablets from stomach
- Protect the API
- Mechanical strength
What are the three different types of coatings on tablets?
- Enteric
- Film
- Sugar
In the tableting manufacturing process, where does coating appear?
- Near the end
2. Before packaging
How are coatings added to the tablet?
- Coating is in solution and sprayed onto the tablet
2. Dried on the surface of tablets and particles
What are the advantages of sugar hard coatings?
- Coats the central core of the tablets to mask taste in drugs which are unpleasant tasting (ibuprofen)
- Protects the active from both light and moisture so it improves stability
- Increases the size of tablet (disadvantage for relatively large tablets)
What are the two examples of excipients that add sweetness?
- Sucrose
2. Glycerol
What are the three examples of excipients that add mechanical strength?
- Croscarmellulose Sodium
- Gelatin
- Gum Arabic
What is the disadvantage of sugar coating?
Can delay the rate of dissolution and disintegration
Describe the purpose of a film coating?
- Thin layers of inactive excipients thinly coated onto the tablets
- Acts the same as sugar coating to mask flavour to protect it from sunlight and moisture
- Dissolves very quickly with contact with an aqueous environment or mechanical damage
What are examples of polymers to create the film coat?
- HPMC
- Shellac
- Methylcellulose
- Polyvinylacetate phthlate
What are examples of solvents used to create the film coat?
- Water: high surface tension
- Alcohols: ethanol
- Ketones: acetone
- Chlorinated Dichloromethane (DCM)
What are examples of plasticisers used to create the film coat and the reason why they are used?
- Adds mechanical flexibility
- Lowers glass transition temperature between polymer chains to increase free volume, elasticity and softness of film
- Examples: PEG and citrate containing esters
What are examples of colourants, flavours and anti-tack agents that are used to create the film coat?
- Colouants: Organic or inorganic colourants
- Flavours: Asparatimine Fruit Spirits
- Anti-tack Glycerol monostearate (GMS) and talc
How is the dissolution profile affected by film coating?
Not affected much at all due to the thickness being very thin
What is the purpose of sustained release tablets?
- Alter release from dosage form and provides a more sustained release of active thoughout the time it’s in the body or to protect it
- Increases the time for the GI tract to absorb it, mainly the small intestine that absorbs most drugs
What is the standard dosing in terms of drug concentration and time in the body?
Initially the drug concatenation increases as time goes by but as soon as it reaches it’s half life there’s a decrease
What can repeat action of the dosing do?
Determines which coating will delay the release
Describe what delayed release is?
Release of API is delayed from transmission in the stomach (enteric)
Describe what repeat action release is?
The coating will allow the tablet to release it’s API for a second time round to allow for continuous effect
Describe what prolonged/sustained release is?
Takes longer to get to the required therapeutic
Describe what constant release is?
Constant rate release and constant plasma concentration
What is the reason behind modified release tablets?
- Less change in blood levels
- Reduces frequency of dosing
- Reduced side effects
- More convenience and increases compliance to take drug
- Reduction in health care costs
What must patients show in order to be eligible for modified release tablets?
- Must exhibit neither slow or fast rates of absorption
- Must be uniformly absorbed to control the blood levels by the drug itself
- Must be administered in small doses
- Must have a good margin of safety
- For chronic rather than acute conditions
Describe what enteric coating is?
- Relating to or occurring in the intestines
- Delays the breakdown of the tablet until it reaches the small intestine (pH dependent depending on area of tablet)
- Surrounds the API core with excipients
Describe the purpose of the duodenum?
- Site of most chemical digestion
- Usually contains the chemicals produced by the liver, gall bladder and pancreas over here
- Absorption of vitamins, minerals and other nutrients (especially iron)
- Residency time is relatively short so may not be the best area for drug absorption (1 hour)
Describe the purpose of the Jejunum?
- Mucosa surface is covered in villi
- Best area for nutrient absorption
- Good vascular supply
- Slight increase in pH compared to duodenum
Describe the purpose of the ileum?
- Smaller in diameter and thicker walls than the other areas of intestine
- Main role is to absorb vitamin B12 and bile salts
- Contains peyers patches that contain large amounts of lymphocytes
Why do we enterically coat tablets?
- Local or systemic action
- Protects the stomach from the drug
- Allows the acid to not react with the drug so it can travel to the intestines
- Improved bioavailability
Give examples of different forms of enteric coatings?
- Cellulose acetate phthalate
- Polyvinyl acetate phthalate
- Acrylates (Eudragit)
How does enteric coated tablets affect dissolution and disintegration?
Directly affects disintegration and dissolution depending on the rate the patient absorbs the tablet
Give examples of drugs that are commonly used as enteric coatings and why?
- Aspirin and naproxen: dissolves in the stomach acid and can cause stomach ulcers
- Omeprazole: broken down in stomach acid and activates in the small intestine
- Sulfasalazine: treatment of arthritis (drug has to dissolve in stomach) and Crohn’s disease (drug has to dissolve in small intestine)
Give examples of polymers that are used to form enteric coatings?
- Shellac
- Cellulose acetate phthalate
- Hypromellulose phthalate
- Methacrylic acid
(Cover pH range of 4.5 to 7)
What are Eudragits?
- Name for a family of polymers with varying properties
2. Can be a carboxylic acid or ester depending on the situation
How are Eudragits applied in reality when it comes to drugs?
- When there’s an increase in pH, it loses it’s H+ and becomes more soluble
- When in ester form, it’s more hydrophobic so it takes longer to dissolve
Explain the disintegration test for E/C tablets?
- Introduce one tablet into each tube
- Place in 0.1M HCl and leave for 2 hours (Check for no cracks)
- Place in phosphate buffer 6.8 pH and leave for 1 hours
- Tablets pass the test if all six have disintegrated
Explain how repeat action tablets work?
- Two layer of tablets that are separated by enteric coating
- First dose gives a rapid onset of action
- Enteric coating delays the second doses onset of action
