Coating of Solid Dosage forms

Question 1

What are some reasons to coat tablets?

Answer 1

• mask taste (original purpose)
• help with swallowing
• controlled or modified release
• improve mechanical strength and flow
• protection from crumbling in high porosity
• reduce irritation of the GI tract or protect drug from from acidic environment
• colours for identification and improved appearance
• reduce interaction between components

Question 2

What are the types of tablet coating?

Answer 2

1. Sugar coating
2. Film coating
3. Press (compression) coating
4. Other → enrobing, gel dipping, hot-melt coating

Question 3

What is the equipment used for sugar coating tablets?

Answer 3

Rotating sugar-coating pan with supply of drying air and extraction system to remove dust and moisture

Question 4

What is sugar coating?

Answer 4

Deposition of aqueous sucrose solution (or sugar alcohols like sorbitol → “sugar free”)

Question 5

What are the steps in sugar coating?

Answer 5

1. Sealing
2. Subcoating
3. Coating
4. Colouring
5. Smoothing
6. Polishing
7. Printing

Question 6

What happens in the sealing step of sugar coating?

Answer 6

Application of polymer coating to tablet core to protect it from moisture, light and oxidation; typically alcohol solutions of 10-30% of specialized resins or polymers are used

Shellac → mixture of aliphatic and alicyclic hydroxy acids and polyesters

Cellulose acetate phthalate (CAP) and polyvinyl acetate phthalate (PVAP) are most commonly used

Question 7

Why is shellac no longer used in the sealing step of sugar coating?

Answer 7

Can compromise bioavailability due to natural polymerization

Question 8

What happens in the subcoating/coating step of sugar coating?

Answer 8

Subcoating → enhances mechanical strength of tablet; subcoating syrup solution is added in small quantities and alternated by subcoating powder in 3-8 layers

Coating → gives 30-50% weight increase of the tablet, rounds off edges of tablet; coating syrup applied stepwise alternated with coating powder for up to 40 layers

Question 9

What is an example of subcoating syrup?

Answer 9

• gelatin
• acacia gum
• sucrose
• tween 80
• water qs

Question 10

Example of subcoating powder formulation

Answer 10

• calcium carbonate
• colloidal slilica
• talc
• sucrose
• acacia gum

Question 11

Example of coating syrup

Answer 11

• sodium CMC
• Colloidal silica
• titanium dioxide
• sucrose
• starch
• water qs

Question 12

What is involved in the colouring step of sugar coating?

Answer 12

Multiple applications of syrup solutions with colouring materials; usually with the last coating layer

→ colourants include water-soluble dyes, water-insoluble pigments (titanium dioxide, iron oxide)

Question 13

Are pigments or dyes preferred in the colouring step of sugar coating?

Answer 13

Pigments because they are less prone to move to the surface and cause mottling

Question 14

What is involved in the smoothing step of sugar coating?

Answer 14

Smoothing → application of a simple syrup solution; may contain titanium dioxide (1-5%) as opacifier

Question 15

What is involved in the polishing step of sugar coating?

Answer 15

Polishing → gives glossy finish to tablets by application of wax mixtures

Question 16

Is printing done before or after the polishing step?

Answer 16

Doesn’t matter

Question 17

What are some potential problems with sugar coating?

Answer 17

• breakage of tablets during tumbling process
• non-uniform coating due to poor mixing
• twinning (tablets sticking together) → from improper drying
• colour migration during drying when using water-soluble dyes
• rough tablets may result in marble-like appearance during polishing
• cracks and fissures from permeation of moisture into the core

Question 18

What is film coating?

Answer 18

Involves the deposition of a thin, uniform polymer coating onto the surface of tablets, capsules and multiparticulates

Question 19

What are some advantages of film coating?

Answer 19

• minimal weight increase (5% of tablet core weight)
• does not change original shape of core
• reduced processing time; increased efficiency and output
• allows for modified release

Question 20

What are the three rules for avoiding dose dumping?

Answer 20

1. film coating must be mechanically sound and resist rupture on ingestion of the dosage form
2. sufficient coating must be applied uniformly across the surface of material to be coated
3. dosage form must not be chewed or crushed

Question 21

How does the solubility of the coating relate to the release rate?

Answer 21

Insoluble → extended release

Water soluble → immediate release

Question 22

What are the three most common polymers used for film coating?

Answer 22

• cellulose derivatives
• acrylic resin
• polyvinyl derivatives

Question 23

Why are insoluble pigments preferred colourants for film coating?

Answer 23

• reduce permeability of coating to moisture → improves product stability
• bulking agent → increases overall solid content in coating dispersion
• less colour migration
• opacifying → improved stability of photolabile API

Question 24

Is it possible to have a drug inside the coating?

Answer 24

YES

Question 25

What is the most commonly used equipment in coating and how does it work?

Answer 25

Side-vented pan/perforated pan coater → adequate mixing and agitation of the tablet bed, sufficient heat input in drying air provides latent heat of vaporization of aqueous solvents

Question 26

What is the difference between airless and air spray coating?

Answer 26

Airless → pumped under pressure through small nozzle to achieve atomization; used in large scale coating operations using organic solvents Air → compressed air is used to atomize coating liquid; used in small scale operations pr aqueous coating formulations

Question 27

How does a continuous film-coating process work?

Answer 27

Tablets are rotated down elongated perforated pan and spray nozzle coats the tablets

Question 28

What is fluidized bed coating typically used for?

Answer 28

Commonly used to coat for taste masking, enteric and ER coatings of multiparticulates \*\*also used for drying and granulating

Question 29

What are the three devices used in fluidized bed coating?

Answer 29

1. Wurster process (bottom spray) 2. Top spray process (granulation or convention mode) 3. Rotor process (tangential spray) → double chamber

Question 30

What are the advantages, disadvantages and applications of top spray coating?

Answer 30

Advantages → large batch sizes, simple setup and easy access nozzle Disadvantages → limited applications Applications → aesthetics and enteric coatings (not recommend for SR or tablet coating)

Question 31

What are the advantages, disadvantages and applications of bottom spray/Wurster process?

Answer 31

Advantages → moderate batch sizes, uniform and reproducible film characteristics, widest application range Disadvantages → tedious setup, cannot access nozzles during process, tallest fluid bed machine Applications → SR, enteric release, layering, aesthetics (not recommended for tablet coating)

Question 32

What are the advantages, disadvantages and applications of tangential spray/rotary mode?

Answer 32

Advantages → simple set up, nozzle access during process, high spray rate, shortest machine Disadvantages → mechanical stress on product Applications → good for layering, SR, enteric coating (not recommended for friable products/tablets)

Question 33

What are some advantages and disadvantages of press coatings?

Answer 33

Advantages → incompatible materials can be formulated together, no solvent needed Disadvantages → formulation and processing of the coating layer requires some care, problems with lamination

Question 34

What are some potential problems with film coating?

Answer 34

* picking (wet tablets stick and pull film of surface) * orange peel (roughness) * mottling * twinning * cracking and edge chipping * wrinkling or blistering (film detaches from tablet) * tablet logo bridges and infilling logos

Question 35

What are the most important aspects of coated tablets?

Answer 35

Appearance and drug availability

Question 36

What are the standards tests for coated tablets?

Answer 36

* content and weight uniformity * tablet breaking force * friability * dissolution test * disintegration test

Question 37

What is the difference in time frame for the disintegration test for film versus enteric coating?

Answer 37

Film → 30 minutes Enteric → 1 hour