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

2. Tablet Coating

3. SUGAR COATING
Sugar coating is a multistage process and can be divided into the
following steps:
1. Sealing
2. Subcoating
3. Smoothing
4. Coloring
5. Polishing
6. Printing

4. Sealing
• To prevent moisture penetration into the tablet core, a seal coat
is applied. This is specially needed in pan-ladling processes, in
which localized over wetting of a portion of the tablet occurs.
• Without a seal coat, the over wetted tablets would absorb
excess moisture, leading to tablet softening or disintegration
and affecting the physical and chemical stability of the
finished product.
• In spray process, over wetting does not occur and the
application of subcoats and further coats can be adjusted which
can eliminate the seal coating step.

5. Sealing
• Shellac is an effective sealant, but tablet disintegration and
dissolution times tend to lengthen on aging because of the
polymerization of the shellac.
• Zein has also been used as an another effective sealant which
does not lengthen tablet disintegration and dissolution time.
• Besides, some synthetic polymers such as cellulose acetate
phthalate (CAP) or polyvinyl acetate phthalate (PVAP) are
also being used as sealant.

6. Subcoating
• The subcoating is applied to round the edges and build up the
tablet size. Sugar coating can increase the tablet weight by 50
to 100%
• The subcoaing step consists of alternatively applying a sticky
binder solution to the tablets followed by a dusting of
subcoating powders and then drying.
• Subsequent subcoats are applied in the same manner until the
tablet edges have been covered and the desired thickness is
achieved.

7. Subcoating
• For spray processes, a subcoating suspension containing both
the binder (e.g. sucrose) and the insoluble powder (e.g.
calcium carbonate) is sprayed intermittently on the tablet bed.
• Antiadherents such as talc may be used to prevent tablets
sticking together.
• Polysaccharide gums, such as gum acacia, may also be added
as a binder in order to reduce brittleness.

8. Smoothing
• The purpose of the smoothing step is to cover and fill in the
imperfections in the tablet surface caused by the subcoating
step and to impart the desired color to the tablet.
• To facilitate the application of the coloring layer which
requires a smooth surface, subcoated tablets are usually
smoothed out by applying a sucrose coating that is often
colored with titanium dioxide to achieve the desired level of
whiteness.

9. Coloring
• Nearly all sugar coated tablets are colored.
• Color coatings usually consist of sucrose syrups containing the
requisite coloring materials.
• Traditionally, water soluble dyes have been used for color
coating.
• Nowadays, to speed up the coating process and minimize
color migration problems, dyes have been replaced with
pigments.

10. Polishing
• Once the color coatings layers have been applied and dried, the
tablet surface tends to be smooth but somewhat dull in
appearance.
• To achieve the glossy finish, a final stage involving the
application of waxes is employed.
• Suitable waxes include beeswax, carnauba wax or candelila
wax, applied as finely ground powders or as
suspensions/solutions in an appropriate organic solvents.

11. Printing
• For sugar coated tablets identification (manufacturer logo,
product name or other code) can be achieved by means of a
printing process, which is typically an offset gravure process,
using special edible inks.
• Alternative printing processes, such as inkjet and pad printing
processes, have also gained acceptance.

12. Sugar coating defect
Common sugar coat defects include:
 Tablets that are rough in appearance
 Tablets that are smooth but dull in appearance
 Tablets that have debris stuck to the surface
 Tablets exhibiting poor color uniformity
 Tablets that splits on storage as a result of inadequate drying

13. COATING OF MULTIPARTICULATES
• Coated multiparticulates, often referred to as pellets or beads,
commonly form the basis for a wide range of modified-released
dosage forms.
• Typically used for extended and delayed released products
• In these systems, the dosage of the drug substances is divided
on a plurality of subunit, typically consisting of thousands of
spherical particles with diameter of 0.5-2.00 mm

14. Benefits of coated multiparticulates
• Capitalizing on small size (typically 0.5-2.0 mm)
• Minimizing irritant effects
• Reducing the consequences of imperfect coatings
• Reducing the impact of poor coating uniformity
Please go through the book (Pharmaceutics by Aulton page 511-512)
for details.

15. Types of multiparticulates
• Drug crystals
• Irregular granules
• Spheronized granules
• Drug-loaded non-pareils
• Mini tablets
Figure: page 512 (Pharmaceutics by Aulton)

16. Drug-loaded non-pareils
• These are preformed spherical particles about 1 mm in
diameter consisting primarily of sucrose and starch.
Application of the drug uses any of following two methods:
• A powder dosing technique involving alternate dosing of
powder (containing the drug substances) and binder liquid
onto the surface of the non pareils until the required dose of
the drug has been achieved

17. Drug-loaded non-pareils
• Spray application of drug, either suspended or dissolved in a
suitable solvent (usually water) containing also a polymer
binder (e.g. HPMC or PVP) onto the surface of the non
pareils.
Coated drug loaded non-pareil

18. Mechanisms of drug release from multiparticulates
 Diffusion
• Diffusion is primarily a process whereby drug will partition
into the film coat membrane and permeate through it.
• The rate at which the drug is released by this mechanism is
influenced by the drug concentration gradient across the
membrane, the thickness of the membrane, the solubility of
the drug in the membrane and the permeability coefficient
governing passage of the drug through the membrane.

19. Mechanisms of drug release from multiparticulates
 Osmosis
• Once water has passed through the film coating, dissolution
of soluble components (excipients and drug) within the core
can allow an osmotic pressure to be generated inside the
coated particle that will influence the rate at which the drug
will be pushed out through pores or a preformed aperture in
the membrane.

20. Mechanisms of drug release from multiparticulates
 Dialysis
• Dialytic effects describe conditions where water-filled
channels are formed in a micro porous membrane (often
created by the imperfections common to many applied film
coatings) through which drug in solution can pass. The key
factors influencing drug release by this mechanism include
the length and tortuosity of these channels, as well as the
solubility of the drug in water.

21. Mechanisms of drug release from multiparticulates
 Erosion
• Some coatings are designed to erode gradually with time,
thereby releasing the drug contained within the pellet in a
controlled manner.
• Examples of these types of coatings are usually those that
consist of natural materials such as shellac or waxes and fats
that become soft enough to facilitate erosion as the coated
multiparticulates are subjected to intense agitation as they
pass through the GIT.