Module 1 - Tablets (Part 3)

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Module 1 - Tablets (Part 3) NIPER JEE Preparation Material

In the part 3 of this module, we will learn the following on the tablets. In this module, we will study only important points for NIPER JEE. Kindly read the references given at the end, if you need more comprehensive information on any topic.

Learning objectives:

Tablet coating

Equipments for tablet coating

1. Conventional coating pan

* Pellegrini pan system

* Immersion sword system

* Immersion tube system

2. Perforated pan system

* Accela-Cota system

* Hi-Coater system

* Glatt coater system

* Driacoated system

3. Fluidized bed coater

Important: Pan speeds of 10-15 RPM - non-aqueous film coating

Pan speeds of 3-10 RPM - aqueous film coating

Sugar coating

Role of each step

Sealing/Water proofing: provides a moisture barrier and harden the tablet


Common materials used as sealants:

* Shellac (dissolution and disintegration time may increase over time due to polymerization - result in low bioavailability of tablets)

* Zein

* Oleic acid

* Propylene glycol

* PEG 4000

* Cellulose acetate phthalate (CAP)

* Polyvinylacetate phthalate

Subcoating: round off the tablet edges and increase the tablet size.

This step involves the application of gum based solution followed by dusting with powder and then drying.

This step causes a 50-100% increase in the weight of tablets.

Solutions used for subcoating are gelatin, acacia, sugar, and corn syrup.

Subcoating/dusting powders are:

* Kaolin

* Dextrose

* Calcium carbonate

* Cane sugar

* Acacia

* Corn starch

* Talc

* Calcium sulfate

Syrup coating (smoothing): smoothes out the subcoated surface. To give a tablet its colour.

Polishing: produces the characteristics gloss/luster.

* Carnauba wax

* White beewax

* Paraffin wax

* Naphtha as solvent for the wax

Film coating

Pan-pour methods

It is not used much now; have several disadvantages:

* Slow

* The method relies totally on the skills of an operator

* It require other steps such as drying process to remove solvents

* Aqueous based coatings are not suitable for this method - overwetting of tablets

Pan-spray methods

Are preferred method for coating due to increased efficiency and automation in the process.

Film formers

Hydroxy Propyl Methyl Cellulose (HPMC)

It is a polymer of choice for air suspension and pan spray coating systems because of solubility characteristic in gastric fluid, organic and aqueous solvent system.

Disadvantage: when it is used alone, the polymer has tendency to bridge

or fill the debossed tablet surfaces. So mixture of HPMC and other polymers/ plasticizers is used.

Methyl Hydroxy Ethyl Cellulose (MHEC)

It is not frequently used as HPMC because soluble in fewer organic solvents.

Ethyl Cellulose (EC)

Insoluble in water and gastric fluids. Hence it is used in combination with water-soluble additives like HPMC and not alone.

Unplasticized ethyl cellulose films are brittle and require film modifiers to obtain an ideal film formulation.

Aquacoat is aqueous polymeric dispersion of ethyl cellulose manufactured by FMC Corporation, USA. It is used to achieve the modified release of the formulations.

Hydroxy Propyl Cellulose (HPC)

Soluble in water below 40 C (insoluble above 45 C), gastric fluid and many polar

organic solvents.


* available in four viscosity grades i.e. K-15, K-30, K-60 and K-90.

* Average molecular weight of these grades is 10, 000, 40, 000, 160, 000 and

360, 000 respectively.

* K-30 is widely used as tablet binder and in tablet coating.

Polyethylene glycols (PEG)

Lower molecular weights PEG (200-600) are liquid at room temperature and are used as plasticizers. High molecular weights PEG (900-8000 series) are white, waxy solids at room temperature. Combination of PEG waxes with CAP gives films that are soluble

in gastric fluids.

Acrylate polymers

* It is marketed under the name of Eudragit. Eudragit E is cationic co-polymer based on Poly(methyl)acrylates.

* Eudragit E is freely soluble and swellable in gastric fluid up to pH 5.

* Eudragit RL & RS are co-polymers with low content of quaternary ammonium groups.

* They produce films for delayed action (pH independent).

Enteric materials

Ideal enteric polymer: should be soluble at PH 5 or above PH 5.

Cellulose acetate phthalate (CAP)

* Widely used

* Soluble only at PH above 6.

* Aquateric:

It is patented aqueous dispersion of CAP marketed by FMC Corporation, USA.

* Particle size of CAP in Aquateric

0.05-3 micron

Acrylate polymers

Acrylate Polymer

Solubility (PH)


Eudragit L


As organic solution (isopropanol), solid and aqueous dispersion

Eudragit S


Available only as organic solution (isopropanol) and solid

Hydroxypropyl methylcellulose phthalate

Popular brand names: HP-50, HP-55, HP-55-S

It is soluble at lower PH (5 to 5.5) than other polymers.


To dissolve the polymers.

Ideal solvent is water.


Function: it change the physical properties of polymer.

* It changes the polymer-polymer interactions

* It optimizes the flexibility, tensile strength, and adhesion properties of the film.

Commonly used plasticizers:

* Castor oil

* Propylene Glycol (PG)

* Glycerin

* Lower molecular weight (200-400 series) PEG

* Surfactants, etc.

For aqueous coating PEG and PG are more used while castor oil and spans used for organic-solvent based coating solution.


Concentration: (light shade)-0.01%- (dark shade )2%

Commonly used Colorants

* Lakes-most preferred

* Iron oxides

* Anthocyanins

* Caramel

* Carotenoids

* Chlorophyll

* Flavones

* Turmeric

* Carminic acid

Other special coloring agents; which doesn't require milling equipments

Opalux: for sugar coating

Opaspray: for film coating

Opadry: film coating concentrate

Opaquant extenders

They increase the film coverage of colors; thereby they decrease the amount of expensive colorants needed for the film coating.


Titanium dioxide (most commonly used)


Aluminum oxide

Calcium sulfate

Magnesium oxide

Aluminum hydroxide

Film defects

Sticking and picking

It is defect where isolated areas of film are pulled away from the surface

when the tablet sticks together or to the coating pan (due to overwetting) resulting an exposed area of core of tablet.

Preventive measures:

* Increase the inlet air temperature

* Decrease the rates of application of coating solution


Definition: roughness of film coating. The polymer is dried before reaching the base of coating pan.

Preventive measures:

Reducing the degree of atomization

Moving the atomizer deep into the coating pan

Orange peel effect

Definition: It is surface defect resulting in the film being rough and nonglossy.

Appearance is similar to that of an orange.

Preventive measure:

* Use mild drying conditions

* Use additional solvents to decrease viscosity of solution.

Bridging and filing

Definition: the film shrink and pull away from the bisects of tablet

Preventive measure:

Increasing the concentration of plasticizer or change the plasticizer.


Definition: too rapid drying of solvents in polymer

Preventive measure:

* Use mild drying conditions


Definition: coating becomes dull immediately or after prolonged storage at high temperatures

Also called blooming.

Preventive measure:

Decrease plasticizer concentration and increase molecular weight of plasticizer

Color variation

Definition: A defect which involves variation in colour of the film

Preventive measure:

Proper mixing, reformulation with different plasticizers and additives or use

mild drying conditions


Definition: It is defect in which the film either cracks across the crown of the tablet

(cracking) or splits around the edges of the tablet (Splitting)

Preventive measure:

Adjusting the plasticizer type and concentration

References and further reading

Banker, G. S., & Anderson, N. R. (1991). The theory and practice of industrial pharmacy; Lachman, L. 3rd edition.

Remington, J. P. (2006). Remington: The science and practice of pharmacy (Vol. 1). D. B. Troy, & P. Beringer (Eds.). Lippincott Williams & Wilkins.

About the Author

Kapil Pal's picture
Author: Kapil Pal

Kapil Pal holds a Bachelor's and Master's degree in Pharmacy. He is a registered pharmacist based in India. He had earned a national scholarship to study at the prestigious National Institute of Pharmaceutical Education and Research, Punjab, India. He has a lot of medical articles to his credit, published in the Drug Today Medical Times, India. He authored three chapters for the Encyclopaedia on Pharmacology and Society, Sage Publications, which is currently in the publishing stage. He has also published many business cases in Sage Publications.He has also authored a book on Ebola Virus Disease, titled Ebola: Is There Any Cure? He is currently working in a UK based pharmaceutical consultancy company.

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