W10 Tablet coating

Question 1

What are the objectives of tablet coating?

Answer 1

• 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

Question 2

What are the types of coating? (3)

Answer 2

Film
Sugar
Compression

Question 3

Film coating

Answer 3

• Most popular
• Spray of liquid coating system
  -Polymer-based formulation

Question 4

Sugar coating

Answer 4

• More traditional
• Successive applications of sucrose-based formulations

Question 5

Differences between sugar and film
coating?
Sugar coating:

Answer 5

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

Question 6

Differences between sugar and film
coating?
Film coating:

Answer 6

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

Question 7

What is Compression coating?

Answer 7

• Less popular
• Compaction of granular material round a preformed tablet
• Specialist modified release tablets

Question 8

Film coating:

Answer 8

• 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

Question 9

Film-coating formulations usually comprise of? (4)

Answer 9

• Polymer
• Plasticiser
• Colourants
• Solvent/vehicle

Question 10

Film coating polymers:
Solubility?
Permeability?
Viscosity?
Mechanical properties?

Answer 10

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

Question 11

Film coating polymers – immediate
release

Answer 11

Immediate release coatings do not affect tablet disintegration, drug dissolution or drug bioavailability

Question 12

Film coating polymers – enteric film formers
Why is enteric coating used?

Answer 12

• 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

Question 13

Film coating polymers – sustained
release
(prolonged, extended)

Answer 13

• Sustained release coatings resist dissolution or disruption at all pH
  -Drug release is diffusion-controlled

Question 14

Plasticisers:
What is their purpose?
Examples?
When are they used?

Answer 14

• 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)

Question 15

What are some examples of Colourants?

Answer 15

• 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

Question 16

Solvents (4)

Answer 16

• 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

Question 17

What is sugar coating?

Answer 17

A multi-step process
Sucrose solution spray, Wet & recrystallise (tablet core), Layer build up

Question 18

Dry Sugar coating (for info)

Answer 18

Sealing
Sub-coating
Smoothing
Colouring
Polishing
Printing

1. Prevent watering
2. Thick coat of sucrose solution, also containing: Calcium carbonate as bulking agent, Talc to prevent sticking, polysaccharide gum to dec brittleness
3. Thin sugar coat also containing dyes or pigments
4. Thin sugar coat, also containing dyes or pigments
5. Mix with beeswax
6. Ink ket or pad printing

Question 19

Wet sugar coating (for info)

Question 20

Newer technology:
What are the types of coating?

Answer 20

1. Electrostatic coating
   * Create coatings with highly distinctive patterns (brand identification)
   * To load very low-dose drugs onto tablets
2. Vacuum film coating
   * Low energy requirements
   * High coating efficiency

Question 21

What are the Ideal characteristics of coated tablets? (3)

Answer 21

• 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

Question 22

What are the types of extended-release tablets? (4)

Answer 22

• 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