Coating of Tablets

Pharmaceutics III
Lecture 4

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 Learning Objectives

By the end of this lecture, the student will be able to:

1.Identify the rationale for coating solid dosage forms.

2. Differentiate the different types of tablet coatings.
3. Compare the advantages and the limitations of different types of coatings.
4. Explain the significance of enteric coating.
5. Discuss the use of pH sensitive polymers used in enteric coating.
6. Give examples of polymers and materials used in coating.

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 Tablet Coating

❑ Coating (def): is a process by which an essential dry, outer layer of coating material is applied to
the surface of a dosage form in order to obtain specific benefits such as product identification or
modifying drug release.

❑ Coated tablets (def): are covered with one or more layers of mixture of various substances to
confirm some benefits and properties to the dosage form over the uncoated one.

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 Reasons for Coating

• To prevent drug-induced irritation to the oesophagus and stomach.

• To protect the content of tablets from stomach acids (preventing
Therapy degradation and inactivation).
• To increase drug effectiveness.

• To protect the drug from the environment (light and moisture), thus
potentially improving product stability.
• To mask the taste of bitter or unpleasant drugs.
Production
• To mask any batch differences in the appearance of raw materials.
• To facilitate the rapid product identification by the manufacturer and
user.

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 Types of Coating Processes

Film coating

Types of coating
Sugar coating
processes

Press coating.

Left to right: Vitamin-C uncoated tablets,

(Advil) Ibuprofen sugar-coated tablets,
(Motrin) Ibuprofen film-coated tablets.

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 1. Sugar Coating

❑ The traditional method for coating pharmaceutical products.

❑ Sugar coatings are composed of ingredients that are soluble in water.
❑ Sugar coated tablets are smooth, rounded, with even color coverage and a
glossy finish.
❑ Typically, tablets are sugar coated by a panning technique, using a
traditional rotating sugar coating pan with a supply of drying air, and a
system to remove dust and moisture.

Watch: sugar coating!

Traditional sugar
coating pan
https://www.marketwatch.com/press-release/sugar-coated-tablets-market-2019-global-industry-overview-by-size-share-future-growth-development-revenue-top-key-
players-analysis-and-growth-factors-up-to-2024-2019-04-11
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 1. Sugar Coating
Sugar coating is a multistage process and be divided into the following steps ( in order):

1. Sealing tablet core

2. Subcoating

3. Smoothing

4. Coloring
5. Polishing
6. Printing

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 1. Sugar Coating
Sugar coating is a multistage process and be divided into the following steps ( in order):
1. Sealing of the tablet core:
Purpose: to protect the tablet core from water penetration.
How: by the application of a water impermeable polymer (waterproof or sealing coat) such as
Shellac, cellulose acetate phthalate and polyvinyl acetate phthalate, which protects the core from
moisture, increasing its stability.

2. Subcoating:
Purpose: to round off the tablet edges and build tablet size.
How: by adding bulking agents (e.g. calcium carbonate) and anti-adherent (e.g. talc) in
combination with sucrose solution.

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 1. Sugar Coating
Sugar coating is a multistage process and be divided into the following steps ( in order):
3. Smoothing:
Purpose: to remove the rough layers formed in step 2.
How: by applying sucrose syrup mixed with titanium dioxide to achieve the desired level of
whiteness to smooth out the surface of tablet.

4. Coloring:
Purpose: for aesthetic (appealing) purposes.
How: by applying sucrose syrups containing the required colors.

https://patents.google.com/patent/US4274830A/en

https://www.koelcolours.com/products/pharmaceutical
s/organic-colours-for-food-applications.php
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 1. Sugar Coating
Sugar coating is a multistage process and be divided into the following steps ( in order):
5. Polishing:
Purpose: to achieve the glossy finish of the sugar-coated tablets.
How: by applying waxes (such as beeswax or carnauba wax) in form of either fine powder or as a
solution in an organic solvent.

6. Printing:
Purpose: to identify the tablets by the logo, name, or dosage strength.
How: by using special edible inks.

Sites to identify tablets by printing:

https://www.rxlist.com/pill-identification-tool/article.htm
https://pillbox.nlm.nih.gov/
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 1. Sugar Coating
Common Sugar-Coating Defects:

❑ Rough appearance due to wax filling the surface during the polishing stage.

❑ Dull appearance due to insufficient polishing.

❑ Tablets split on storage due to inadequate drying.

❑ Poor color uniformity due to uneven distribution of coloring solution.

❑ Cracking due to expansion of the tablets during coating caused by moisture.

Sugar coating defects

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 2. Film Coating
❑ The modern and the commonly used process for coating solid dosage forms.
❑ Typically, it involves a single step of spraying a thin film of a polymer material to the surface of
the tablet or a capsule.
❑ The coating liquid (solution or suspension) contains a polymer in a suitable liquid medium with
other ingredients such as colorants and plasticizers.
❑ Film coating may be designated as either:

1. Non-functional coating Immediate-release film

coatings for aesthetics purposes.

2. Functional coating (Modified-release or enteric

coating coating films).

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 2. Film Coating
❑ Film Coating Equipment:
1. Pan Coating:
▪ The common process which involves spraying of the coating material onto a bed of tablets.
▪ Accela Cota is an example of pan coating equipment used for film coating.

https://www.youtube.com/watch?v=oqCsbManpYs
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 2. Film Coating
❑ Film Coating Equipment:
2. Fluid-Bed:
▪ Fluid bed technology helps in achieving fast and uniform coating using air to mix, coat and dry
the tablets at the same time.
▪ Limitation: high friability and dull appearance compared to pan coating process.

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 2. Film Coating
❑ Film Coating Formulations:

Features: Purpose: Water insoluble Traditionally, organic

SOLVENT/VEHICLE
COLORANT
POLYMER

PLASTICIZER
1. Soluble in most to reduce film pigments are more solvents had been
solvents. brittleness (Friability). favourable than water used to dissolve the
soluble dyes because polymer but replaced
2. Acceptable color How? of: with water because of
and taste. plasticizers place significant drawbacks
1. Better chemical
3. Stable in different themselves between stability in light. of organic solvents
environments. the polymer to fill the including
spaces to increase 2. Impermeability to environmental and
4. Pharmacologically water vapor.
film flexibility. health issues.
inert.
3. Better opacity and
5. Compatible with covering ability.
other ingredients.

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 2. Film Coating
❑ Film Coating Formulations:

Examples: Examples: Examples: Examples:

SOLVENT/VEHICLE
COLORANT
POLYMER

PLASTICIZER
For immediate-release Polyols: Polyethylene Iron oxide pigments. Organic solvents:
coating: glycols. Titanium dioxide. methanol/
Cellulose derivatives: Oils/glycerides: Aluminium lakes. dichloromethane
Hydroxypropyl fractional coconut oil combination.
methylcellulose and Diethyl phthalate. Acetone.
Methylcellulose.
For modified-release
coating:
Modified acrylate or
Ethyl cellulose

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 2. Film Coating
Description of Film-Coated Tablets:
❑ Even coverage and color of the coating across the tablets.
❑ No abrasion of tablet edges (no defects).
❑ Logos and break lines should be distinct and not filled.

Common Film Coating Defects:

❑ Visual defects due to imbalance between the coating liquid and dry step
(results in either over-wetted or over-dried tablets).
❑ Film cracking or breakage due to defects in the tablet core which make the
tablet unable to withstand the coating process.

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Major Differences Between Sugar and Film Coating
Features Sugar Coating Film Coating
Tablets
Shape Rounded Retains contour of original core
Appearance Shiny and glossy Not as shiny as sugar coat types.

Weight increase due to 30-50% 2-3%

coating materials
Logo or break line Not possible possible

Process
Stages Multistage process Single stage
Typical batch coating 8 h or longer 1.5-2 h
time
Functional Coatings Possible for enteric Easily adaptable for controlled
coating release or enteric coating. 19
 3. Press Coating
❑ Based on a modification of tableting process.
❑ It involves the compaction of granular material around a preformed tablet core.
❑ At first, tablet core is prepared and moved into another part of the machine contains a larger
die filled with a coating powder.
❑ Then, the tablet core is filled again with more coating powder, before going into a second
compression cycle.
❑ Advantages:
1. Enables incompatible materials to be formulated together (more than one ingredient can
be placed in the core and the other(s) in the coating material).
2. Does not involve the use of volatile solvents.
❑ Disadvantages:
a complex process that requires caution and experience.
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Preformed or pre-
compressed tablet
without the coat

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 Enteric Coating
❑ Enteric-coated tablets (def): conventionally compressed tablets coated with a polymer that
does not dissolve in the acidic condition of the stomach but readily dissolves in the alkaline pH
of the small intestine.

❑ Advantages of enteric coating:

1. Protect drugs from the degradative effects of gastric acidity.
2. Protect gastric mucosa from irritation from certain drugs.
3. Deliver the drug to specific site in small intestine (e.g.: anthelmintics).

❑ The coatings may be applied in multiple portions to build a thick coating or as a thin film coat.

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 Enteric Coating
❑ Polymers that have enteric-coating ability include shellac, cellulose acetate phthalate (CAP),
cellulose acetate butyrate (CAB), and methacrylic acid co-polymers (Eudragit).

❑ Ideal properties of enteric coating materials:

› Resistance to gastric fluids.
› Susceptible/permeable to intestinal fluid.
› Compatibility with most coating solution components and the drug substrate.
› Formation of continuous film.
› Nontoxic, cheap and ease of application.
› Ability to be readily printed.

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Enteric Coating

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Example

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 References

1. Allen L. Ansel's pharmaceutical dosage forms and drug delivery systems. 11th ed. Philadelphia:
Wolters-Kluwer; 2017.
2. Aulton M, Taylor K. Aulton's pharmaceutics.4th ed. Edinburgh: Elsevier; 2018.
3. Dash A, Singh S, Tolman J. Pharmaceutics: Basic Principles and Application to Pharmacy Practice.
1st ed. Amsterdam: Elsevier-Academic Press; 2014.
4. Hussan S. A review on recent advances of enteric coating. IOSR Journal of Pharmacy (IOSRPHR).
2012;2(6):05-11.
5. https://www.pharmapproach.com/?s=coating+process
6. Various materials and images obtained from the web.

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