Coating Flashcards
Why do we coat tablets?
- To mask unpleasant taste/odour
- To protect drug from inactivation in gastric fluids (enteric coating)
- Minimize irritation (GI mucosa)
- To improve mechanical strength and flow
- Reduce interaction
- To modify drug release properties
What are the types of tablet coating?
- Sugar coating
- Film coating
- Press coating
Describe the sugar coating steps (7)
- Sealing
- Subcoating
- Coating
- Colouring
- Smoothing
- Polishing
- Printing
Describe the sealing step in sugar coating
Ex.
- application of polymer coating to tablet core to protect from moisture, light, oxidation
Ex. Shellac, Cellulose acetate phthalate (CAP), Polyvinyl acetate phthalate (PVAP)
Describe the subcoating step & coating in sugar coating
Subcoating
- improves mechanical strength of tablet and protect against moisture
- subcoating syrup and powder in 3-8 layers
Coating
- gives 30-50% weight increase
- coating Syrup and powder up to 40 layers
When is colouring step in sugar coating
- usually with the last coating layer
Ex. water-soluble dyes or water-insoluble pigments
(titanium dioxide, iron oxide)
what is added in the smoothing step in sugar coating
add a simple syrup solution
- contain a low % of titanium dioxide
- approx. 60-70% sugar solids
Describe the polishing step in sugar coating
ex?
gives the glossy finish to tablets
- wax mixtures
Describe the printing step in sugar coating
can be done before or after polishing
What are some problems with sugar coating?
- breakage of tablets during tumbling process
- non-uniform coating due to poor mixing
- twinning (tablets sticking together) due to improper drying before the application
- Colour migration (mottling) during drying when water-soluble dyes are used
- Cracks and fissures from permeation of moisture into core
Describe film coating in general
- involves adding a thin, uniform polymer coating onto the surface of tablets, capsules, multiparticulates (pellets)
- Minimal weight increase (5%)
- significant reduction in processing time
- provide multiple options to modify release of drug
What are the 6 components in a film coating formulation?
- Polymers
- Solvents
- Plasticizer
- Colouring agents
- Anti-adherents
- Surfactants
What are the 2 types of polymers in film coating formulation? which are functional vs non-functional
Immediate release (non-functional)
Modified release (functional)
What are examples of immediate-release coating?
- Cellulose derivatives
- hypromellose or HPMC
- Hydroxypropyl cellulose
2 .Vinyl derivatives
- Polyvinyl alcohol
- Acrylic derivatives
- Methylmethacrylate copolymers
- methacrylic acid copolymers
Explain delayed release
- designed to prevent release in the upper part of the GI tract
- known as enteric coatings or gastroresistant coatings (protect drug & minimize irritation from stomach)
What pH do most effective polymers have for enteric coatings (delayed release)
pH 5-6
Delayed release coating polymers examples
see one note
Explain the polymers of EXTENDED-release coatings?
Ex.
- Polymers are insoluble in water, however (polymer swells and forms a water-permeable membrane allowing for diffusion of drug)
Ex.
- Ethylcellulose (Aquacoat)
- Acrylic resins (methacrylates)
What do you have to be aware of when using extended-release coatings?
How to avoid?
Dose dumping
Avoided if:
- film coating is mechanically sound
- enough coating is applied uniformly
- dosage form is not chewed or crushed prior to ingestion
Disadvantages of using water as solvents in film coating
- slow evaporation, longer drying time
- appearance of picking or peeling or flakes
- mottling (colour migration)
Explain use of organic solvents for film coating
Faster drying
- expensive: efficient venting, plant optimization
- Safety issues: flammable, toxic
What are plasticizers used for?
Examples?
Improves flexibility of the coatings, reduces risk of film cracking
Ex.
polyols: propylene glycol, glycerin, polyethylene glycols
Organic esters: diethyl phthalate, dibutyl sebacate, triethyl citrate, tributyl citrate, triacetin
What type of colourants are preferred in film coatings? why?
Insoluble pigments
- reduce moisture which improves stability
- bulking agents: increase solid content without increasing viscosity
- less colour migration (mottling)
- Opacifying
Purpose of anti-adherents in film coating? examples?
- Reduces stickiness of film
- prevents substrates agglomeration
Ex. Talc, magneisum stearates, glyceryl monostearate, high MW PEGs
