Tablet coating3

1. PHR 221: Pharmaceutical Technology II
Course Teacher: Mohammad Nasir Uddin
Lecturer, Department of Pharmacy, NSU

2. Tablet Coating

3. Types of Film Former or Polymer
 Nonenteric Materials
 Hydroxypropyl methyl cellulose (HPMC)
 Methyl hydroxyethylcellulose
 Ethylcellulose (EC)
 Hydroxypropylcellulose (HPC)
 Povidone
 Sodium carboxymethylcellulose

4. Hydroxypropyl Methylcellulose (HPMC)
 HPMC closely approaches the desired attributes of an ideal
polymer for film coating
 The reasons for widespread use of HPMC include:
1. Solubility characteristics of the polymer in gastrointestinal fluid,
and in organic and aqueous systems.
2. Noninterference with tablet disintegration and drug availability.
3. Flexibility, chip resistance and absence of taste or odor.
4. Stability in the presence of heat, light, air or reasonable levels of
moistures.
5. Ability to incorporate color and other additives into the film
without difficulty.

5. Hydroxypropyl Methylcellulose (HPMC)
 Material of choice for air suspension and pan spray coating
systems
 The interaction of this polymer with colorants is rare
 This polymer is also used considerably in glossing solution
 Limitation:
When used alone, the polymer has the tendency to bridge or fill the
debossed tablet surfaces. A mixture of HPMC and other polymers or
plasticizers are is used to eliminate bridging or filling problems.

6. Povidone
 Available in four viscosity grades which are K-15, K-30, K-60
and K-90. The K number refers to the mean molecular weight of
povidone.
 Povidone (K-30) is widely used in pharmaceutical industry as a
tablet binder and in tablet coating.
 Povidone has excellent solubility in a wide variety of organic
solvents, in water and in gastrointestinal fluids.
 Although povidone is soluble in both acidic and basic fluids, it
can be cross-linked with other materials to produce films with
enteric properties.
 Povidone has been used to improve the dispersion of colorants
in coating solution to obtain a more uniformly colored film.

7. Polyethylene Glycol (PEG)
 PEG is available in a wide variety of molecular weights ranging
from low (200 to 600 series) to high (900 to 8,000 series).
 PEG with low molecular weights are liquid at room temperature
and used as plasticizers for coating solution films.
 PEG with high molecular weights are white, waxy solids at
room temperature and used in combination with other polymers
to modify film properties.
 Coats with high molecular weight PEG are hard, smooth,
tasteless and non toxic but somewhat sensitive to elevated
temperature.

8. Types of Film Former or Polymer
 Enteric Materials
 Cellulose acetate phthalate (CAP)
 Hydroxypropyl methylcellulose phthalate (HPMCP)
 Polyvinyl acetate phthalate (PVAP)
 Acrylate polymer

9. Hydroxypropyl Methylcellulose Phthalate (HPMCP)
 Three grades are commercially available which are HPMC 50,
55 and 55S.
 These polymers dissolve at lower pH (5 to 5.5) than CAP or
acrylate copolymers and thus solubility characteristics may result
in higher bioavailability of some specific drugs.
 For general enteric preparation, HP-55 is recommended
 These polymers are quite stable compared with CAP.

10. Cellulose Acetate Phthalate (CAP)
 CAP dissolves at higher pH (˃ 6) and thus delay the absorption
of drugs.
 It is hygroscopic and relatively permeable to moisture and
gastric fluids in comparison with other enteric polymers.
 CAP films are susceptible to hydrolytic removal of phthalic and
acetic acids, resulting in a change of film properties.
 CAP films are brittle and usually formulated with hydrophobic
film forming materials to achieve a better enteric film.

11. Plasticizers
 Plasticizers are generally added to film coating formulations to
modify the physical properties of the polymer to make it more
usable.
 When incorporated with film former or polymer, plasticizer
increase film flexibility and film tensile strength.
To choose an ideal plasticizer following factors should be
considered :
 Viscosity of the plasticizer
 It’s influence on the final coating solution
 It’s effect on film permeability, tackiness, flexibility, solubility
and taste
 It’s toxicity, compatibility with other coating solution
components

12. Plasticizers
Examples of commonly used plasticizers are:
 Polyols such as polyethylene glycol and propylene glycol
 Organic esters, such as diethyl phthalate and triethyl citrate
 Oils/glycerides, such as fractionated coconut oil
 Surfactants such as polysorbates (Tweens), sorbitan esters
(Spans)

13. Solvents
 The primary function of a solvent system is to dissolve or
disperse polymers and other additives and convey them to the
substrate surface.
Characteristics of an ideal solvent system:
1. It should either dissolve or disperse the polymer system.
2. It should easily disperse other coating components into the
solvent system.
3. Small concentration of polymers (2-10%) should not result in
an extremely viscous solution system (>300cps), creating
processing problems.
4. It should be colorless, tasteless, inert and non-inflammable.
5. It should have a rapid drying rate (the ability to coat a 300
kg/load in 3 to 5 hours)
6. It should have no environmental impact.

14. Solvents
 The most widely used solvents either alone or in combination
are water, ethanol, methanol, isopropanol, chloroform, acetone
etc.
 Water is the solvent of choice because of environmental and
economic considerations.
 Drugs that readily hydrolyze in the presence of water can be
more effectively coated with non-aqueous solvent based
coatings. Such a process might require applying an initial
sealing coat from organic based sub coating followed by
aqueous color and gloss coating.

15. Colorants
 Pharmaceutically acceptable colorants are available in both
water soluble form (known as dye) and water insoluble form
(known as pigments).
 The water insoluble form or pigment is preferred for film
coating formulations due to following reasons:
 Pigments tend to be more chemically stable towards
light
 Provide better opacity and covering power
 Provide a means of optimizing the permeability
properties of the applied film coating

16. Colorants
 Examples of colorants are:
 Iron oxide pigments
 Titanium dioxoide
 Aluminium lakes

17. Opaquant-Extenders
 These are very fine inorganic powders used in coating solution
formulations to provide more pastel colors and increase film
coverage.
 These opaquants can provide a white coating or mask the color
of the tablet core.
 Less colorants need to be used when opaquants are used.
 Most commonly used opaquant is titanium dioxide. Some other
materials are silicates (talc, aluminium silicate), carbonates
(magnesium carbonate), sulfates (calcium sulfates), oxide
(magnesium oxide) and hydroxides (aluminium hydroxide).

18. Miscellaneous Coating Solution Components
 Flavors or sweeteners can be added to mask objectionable odor
or to enhance a desired taste.
 Surfactants can be used to solubilize insoluble ingredients or to
facilitate faster dissolution of the coating.
 Antioxidants can be added to stabilize a dye system to
oxidation and color change.
 Antimicrobials can be added to prevent microbial growth in the
coating composition during its preparation and storage and on
the coated tablets.

19. Film Coating Process
Two methods are used: 1. Pan-Pour and 2. Pan-Spray Methods
1. Pan-Pour Methods:
 The coating solutions are poured over the tablet cores.
 The operator determines the quantity of solution to add, the
method and rate of the pouring, when to apply drying air and
how long or how fast the tablets should be tumbled in the pan.
 Tablets coated by pan pour methods are subjected to alternate
solution application, mixing and drying steps.
 This method is relatively slow and relies heavily on the skills
and technique of the operator to balance the steps to produce an
acceptable product.
 Tablets that are coated by pan pour method almost always
require additional drying steps.

20. Film Coating Process
1. Pan-Spray Methods:
 The introduction of spraying equipment has improved the
coating efficiency process.
 Spraying allows for automated control of liquid application.
 Spray patterns are selected to provide a continuous and across
the tablet bed surface.
 Broad, flat spray patterns are usually chosen by selection of
appropriate nozzle systems so that the entire width of the tablet
bed can be covered by the spray from 1 to 5 nozzles.

21. Film Coating Process
Process Variables
 The variables to be controlled in pan-spray film coating processes
are:
1. Pan variables
• Pan design/baffling
• Speed
• Pan load
2. Process air
• Air quality
• Temperature
• Airflow rate/volume/balance
3. Spray variables
• Spray rate
• Degree of atomization
• Spray pattern
• Nozzle-to-bed distance