Tablet Coating Flashcards
What are the reasons for coating?
Enhance aesthetic appeal and brand image Masks unpleasant taste and odour Enables product to be easily swallowed Reduces frequency of drug dosing Improves product stability Increases shelf life Facilitates product ID during manufacture and prevent wastage during packing and handling Modifies drug release characteristics Provides enteric release properties for release in the intestinal tract.
What is coating?
The application of a coating composition to a moving bed of substrates with the concurrent use of heated air to facilitate th evaporation of the solvents
How does tablet coating improve product stability ?
by protecting the tablet against deterioration from environment, sunlight, temperature variations, moisture, environmental gases etc.
How does tablet coating modify drug release characteristics?
Can achieve a wide range of drug release including
Immediate release
Specific release
Sustained release
Controlled release
As well as targeted drug delivery properties
What are the 3 general types of equipment used in tablet coating?
Standardised coating pan
Perforated coating pan
Fluidised bed (air suspension) coated
What is the standard coating pan?
Consists of circular metal pan mounted angular lay on a stand.
Heated air is directed into the pan and onto the tablet surface and exhausted by the ducts positioned throughout the front of the pan.
The coating solutions are applied onto the tablet by spraying the material onto the rotating tablet bed.
What is a perforated pan?
This consists of a perforated or partially perforated drum which is rotated on its horizontal axis in an enclosed housing
E.g. Accela-Cota and Hi-Coater systems
What are the main components of a perforated pan?
Air supply Exhaust Spray Perforated coating pan Exhaust plenum Tablet bed
What is the principle of fluidised bed (air suspension) systems?
Suspend the tablets in an upward moving stream of air so that they are not in contact with each other
How is fluidisation of tablets achieved?
In a columnar chamber by the upward flow of drying air.
The airflow is controlled so that more air enters the centre of the column.
This causes tablets to rise in the centre.
The movement of tablets is upward through the centre of the chamber no then they fall toward the chamber wall and move downward to reenter the air stream at the bottom of the chamber
What are the main components of the fluid bed Coater?
ExHaust air duct Coating chamber Funnel like modification Support screen Air atomizing nozzle Fluidizing air supply
What are the types of coating?
Sugar coating Film coating (including enteric film coating allowing pH controlled drug release in the intestines which can be adjusted by a combination of polymers and coating thickness).
What are the advantages of sugar coating?
Elegant Attractive High glossy appearance Inexpensive raw materials Widely accepted with few regulatory problems Wide consumer acceptability
What are the limitations of sugar coating?
Tedious and time consuming process (~3-5 days per batch)
Requires expertise of highly skilled technician
Tablet size and weight almost double
There is batch to batch variability even within same batch.
Costly in terms of space, equipment, packaging, shipping
Potential microbial growth and contamination
Hygroscopic
Not as convenient to swallow.
What are the main steps for sugar coating?
Sealing
Sub coating
Smoothing colour coating
Polishing
Why is the sealing step required?
To prevent moisture penetration into the tablet core.
Without a sealing coat, the over wetted tablet would absorb excess moisture resulting in tablet softening or disintegration, affecting the stability of the final product
What are the excipients used in sealing?
Shellac
Zein
HPMC
CAP
Why is dusting powder (talc) used in sealing?
To minimise the risk of clumping and twinning and sticking of tablets to each other .
Why is subcoating conducted?
To round the tablet edges and build up the code weight.
What happens in subcoating?
The tablet weight increases by 50%-100%
This step consists of alternatively applying a sticking binder solution to the tablets followed by a dusting of subcoating powders followed by drying.
What are the dusting powders used in the subcoating step?
Talc Starch Kaolin CaSO4 CaCO3
What does the binding solution in the subcoating step consist of ?
Sugar + Gelatin and/or acacia
How is the binding solution used in the subcoating step made?
Heavy layers of syrup are applied with acacia and gelatin, then sprinkled with powdered sugar and starch.
Talc, acacia, precipitated chalk may also be used.
What is the purpose of smoothing?
Cover and fill in the imperfections in the tablet surface caused by the subcoating step.
Also imparts the desired colour to the tablet.
What are the two main parts of smoothing?
Grossing
Colour coating
Why is grossing required before colour coating?
Premature application of the colouring agent to a rough tablet can produce a mottled appearance which is undesireable
What happens in grossing?
A syrup coat containing suspended powders i.e a grossing coat is added to the surface of the tablet.
Dilute colouring agent can be added to this phase to provided a tented base which facilitates uniform colouring in later steps
What happens in colour coating?
The tablets ae rolled in a light syrup containing dye in a clean pan.
Dyes can either be water soluble dyes or water soluble pigments like lakes used with opacifiers
What is the issue with using water soluble dyes in the colouring process?
In a water soluble dye, the colour migrates to the edges resulting in colouring in the edge and paleness in the centre which is not desired.
Usually use colour lake which is a combination of absorption and water soluble dye and aluminium hydroxide.
The water adsorbs in the heavy metal resulting in the insoluble form of the dye forming a colourlake.
What happens in the polishing process of sugar coating?
A fabric, usually canvas, is impregnated with carnauba wax
Or the wait is dissolved in a non aqueous solvent like acetone and then talc is added.
This is polished onto the tablets
What are the ideal properties of a tablet for tablet coating?
High hardness
Low friability
Good surface adhesion property
What does film coating involve?
The application of thin (20-200μm) polymer based coatings to tablets.
What are the two main types of film coating?
Functional (enteric coating and sustained or controlled release coating)
Non function (to improve the product appearance and stability)
What are the advantages of film coating?
Only adds 10-20μg of weight No need to seal the tablet Easily automated Requires short time frame Coating is non caloric Flexible Method is not as complex Coating is not susceptible to microbial contamination
What are the disadvantages with film coating?
Use of solvents may have adverse effects on safety of worker and environment
Difficult to hide tablet appearance
What are the properties of an ideal film coating material?
Soluble in solvent of choice Capacity to produce elegant looking products Stability No odour, colour or taste Compactibiltiy Pharmacologically inert
What are the basic components of a film coating system?
Polymer Solvent Plasticizer Opaquant extenders Optional ingredients
What are the optional ingredients in the basic components of a film coating system?
Anti tack agent Colour at Flavourant Surfactant Antioxidant Antimicrobial agent
What are the different types of polymers used in film coating?
Celluloses
Acetylate polymers
What are the different types of celluloses used in film coating?
Hydroxypolymethylcellulose (most widely used) Hydroxypolycellulose Ethyl cellulose (used to prepare sustained release coatings)
What are examples of acrylate polymers used in film coating?
Eudragit E (soluble in gastric fluid up to pH 5) Eudragit RL and RS (used for sustained release preparations as they are insoluble in water) Polyethylene glycols (PEGs) Povidone (1-vinyl pyrrolidone)
Why is enteric coating used?
It is intended to resist the gastric acid secretions but dissolve in the intestinal fluid
What happens once an enteric coated tablet reaches the intestine?
The tablet release is identical to that of an uncoated tablet but is displaced by:
- a period of time equivalent to the transit time from the mouth to intestine.
- The time taking for the coating to dissolve
- The gastric emptying rate
What enteric polymers are used?
CAP (cellulose acetate pthalate, most widely used)
Acrylate polymers (Eudragit S and L dissolves in pH 6 and 7 respectively)
Hydroxymethylcellulose pthalate
Shellac
What are the characteristics of an ideal solvent system?
Should dissolve/disperse the polymer system
Be Non toxic and inert
Have no environmental impact
Why should a solvent have no environmental impact?
There are limits on the he acceptable amounts of residual solvents in pharmaceuticals for the safety of the patient
What are examples of solvents?
Water
Alcohols (ethanol, methanol, isopropanol)
Esters (ethyl acetate, ethyl lactate)
Ketones (acetone)
Chlorinated hydrocarbons (chloroform, methylene chloride)
What is the role of plasticizers?
These impart flexibility to the polymers
What does the choice of a plasticizer depend on?
Its ability of solvate the polymer and alter the polymer polymer interactions
The type of plasticizer and its ratio with the polymer is optimised to achieve derived film properties
What are examples of plastizers used?
Castor oil Propylene glycol Glycan Tweens Low molecular weight polyethylene glycans Spans
What sort of colourants are used in film coatings?
Water soluble dyes (FD&C yellow#5, FD&C blue#2) Aluminium lakes (FD&C water soluble dyes) Other lakes (D&C red#6) Inorganic pigments (iron oxides, TiO2, CaSO4, CaCO3) Natural colourants (anthocyanism caramel, carotenoids, chlorophyll, flavones, turmeric etc)
What is the role of opaquant extenders?
Provide more pastel colours and film coverage
Mask colour of tablet code
Reduce requirements of colourants
What are examples of opaque extenders used?
TiO2, Silicates Magnesium carbonate Calcium sulfate Magnesium oxide Aluminium hydroxide
