W10 Tablet coating Flashcards
What are the objectives of tablet coating?
- Protect the API^
- Taste masking
- Ease of swallowing
- Masking variation in core appearance, improving appearance
- Identification
- Product packaging
- Reduce dusting, reduce cross-contamination
- Modified drug release
^ Active pharmaceutical ingredient
What are the types of coating? (3)
Film
Sugar
Compression
Film coating
- Most popular
- Spray of liquid coating system
-Polymer-based formulation
Sugar coating
- More traditional
- Successive applications of sucrose-based formulations
Differences between sugar and film
coating?
Sugar coating:
Appearance- Rounded, with high degree of polish
Weight increase- 30 – 50%
Logo/break lines- Not possible
Stages- Multistage
Batch coating time- 8h or longer
Functional coating-Not usually possible, maybe enteric coating
Differences between sugar and film
coating?
Film coating:
Appearance:
- Retains contour of original core,
not as shiny
Weight increase- 2-3%
Stages: Usually single stage
Batch coating time: ~1.5 – 2 h
Functional coating: Can be adapted for controlled release
What is Compression coating?
- Less popular
- Compaction of granular material round a preformed tablet
- Specialist modified release tablets
Film coating:
- Conventional coating pan- Rotating tablet bed
- Side-vented pan coating- At an angle not greater than 45° to the vertical
- Fluid-bed coating equipment- Coating and drying are combined in one process
Film-coating formulations usually comprise of? (4)
- Polymer
- Plasticiser
- Colourants
- Solvent/vehicle
Film coating polymers:
Solubility?
Permeability?
Viscosity?
Mechanical properties?
Solubility
* Immediate release – water soluble
* Modified release – water insoluble
Permeability
* Taste masking
* Drug stability (vapour, gas, oxygen and water)
Viscosity
* Low for trouble-free spraying
Mechanical properties
* Film strength
* Film flexibility
* Film adhesion
Film coating polymers – immediate
release
Immediate release coatings do not affect tablet disintegration, drug dissolution or drug bioavailability
Film coating polymers – enteric film formers
Why is enteric coating used?
- Enteric coating resists dissolution in the stomach, but not in the intestines
Reasons for use:
* To prevent degradation of acid sensitive API
* To prevent irritation of stomach by certain drugs (e.g. aspirin)
* Delivery of API into intestine
* To provide delayed release of API
Film coating polymers – sustained
release
(prolonged, extended)
- Sustained release coatings resist dissolution or disruption at all pH
-Drug release is diffusion-controlled
Plasticisers:
What is their purpose?
Examples?
When are they used?
- Modify properties of polymers to decrease film brittleness, as most polymers, are brittle and inflexible
Examples:
* Polyols – polyethylene glycols and propylene glycol
* Organic esters – diethyl phthalate and triethyl citrate
* Oils/glycerides, such a fractionated coconut oil
Plasticiser molecules: Insert themselves between polymer molecules
* Increasing free volume and making polymer film more flexible
* Reduces residual stresses within the coating (as it shrinks during drying)
What are some examples of Colourants?
- Permitted colorants in a film coat formulation are water-insoluble colours (pigments)
Examples:
* Iron oxide pigments
* Titanium dioxide
* Aluminium lakes (bonded water soluble colourants with
approved substrate such as fine aluminium hydrate particles)
Pigments are preferred over water-soluble dyes:
* More chemically stable towards light
* Better opacity and coverage
* Does not mottle from solvent migration
Solvents (4)
- Environmental- Global warming and
greenhouse effect with organic solvents - Safety
- Flammable, explosive, toxic
hazards - Financial
-Flame- and explosion-proof facilities, high solvent cost, cost of storage and quality control - Solvent residue- Amount of residual solvent in the film
What is sugar coating?
A multi-step process
Sucrose solution spray, Wet & recrystallise (tablet core), Layer build up
Dry Sugar coating (for info)
Sealing
Sub-coating
Smoothing
Colouring
Polishing
Printing
- Prevent watering
- Thick coat of sucrose solution, also containing: Calcium carbonate as bulking agent, Talc to prevent sticking, polysaccharide gum to dec brittleness
- Thin sugar coat also containing dyes or pigments
- Thin sugar coat, also containing dyes or pigments
- Mix with beeswax
- Ink ket or pad printing
Wet sugar coating (for info)
Newer technology:
What are the types of coating?
- Electrostatic coating
* Create coatings with highly distinctive patterns (brand identification)
* To load very low-dose drugs onto tablets - Vacuum film coating
* Low energy requirements
* High coating efficiency
What are the Ideal characteristics of coated tablets? (3)
- Even coverage and colour
-Across each dosage unit, the batch and from batch to batch - Absence of defects
-Visual
-Functional (modified release) - Processing (imbalance between spraying & drying)
-Over-wetting – tablets getting stuck
-Over-drying – tablet surface erosion or chipping - Compliant with finished product specification
What are the types of extended-release tablets? (4)
- Diffusion controlled (membrane):
Release by diffusion through pores in
a water-insoluble membrane - Diffusion controlled (matrix):
Release by diffusion through pores in
a water-insoluble polymer matrix - Erosion controlled:
Release by erosion of matrix - Osmosis controlled:
Release by osmotic pressure
