Tablet Dosage forms

1. FACTORS
AFFECTING
STRENGTH OF
TABLETS
PREPARED BY:
Ms. Kanchan Singh
M. Pharm, 1st year
Dept. of Pharmaceutics

2. Contents
 Introduction
 Definition Of Tablet
 Various factors affecting strength of
tablets
 References

3. Introduction
 Tablets require certain amount of strength to
withstand mechanical shocks of handling
during manufacturing, packaging & shipping.
 In order to show desired response, each
tablet should posses optimum strength.

4. Definition
 Tablet is a solid unit dosage form consisting of
one or more medicament with excipients
prepared by either compression or molding.

5. Factors affecting strength of
tablets
 Moisture content
 Lubrication
 Particle size & shapes

6. Moisture content
 A small proportion of moisture content is
required in the formulation of the tablet.
 This moisture content is important for the
mechanical strength of the tablet.
 If the moisture content is less, there will be a
increase in the die-wall friction.
 This increase in the friction is due to increase
in the stress ratio, hence the tablet hardness
will be poor.

7. Cont…
 At optimum moisture level, the die-wall
friction is reduced , this is due to the decrease
in stress ratio.
 As the moisture content is increased, there
will be decrease compact strength, this
decrease is due to the reduction in inter
particulate bonding.

8. Generalised plot of
Tablet Strength Vs
Moisture content of
granules

9. Cont…
 Generally moisture content is usually
determined by loss on drying.
 Formula for calculating moisture content in
percentage:-
% moisture content = ( loss in weight ) Χ 100
(Initial weight)

10. Lubricants
 Lubricants are intended to reduce the friction
between walls of tablet & die wall during tablet
ejection from die cavity.
 Lubricants also prevents the adhesion of
tablet material to the dies & punches.
 Lubricants are spread over the surface of
particle which reduces the bond formation
between the particles, which leads to
reduction in inter particle friction, leads to
improve the flow property of the granules.

11. Cont…
 Poor selection or excessive amount of
lubricants results in water proofing the tablet,
resulting in the poor tablet disintegration &
dissolution.
 The addition of proper lubricant is highly
desirable, if tablet material tends to stick to
the dies & punches.
 The level at which the lubricants should be
employed & the degree to which they need to
be added in the granules should be
determined experimentally

12. Effects of Lubricants
 Lubricants at low concentration, decrease the
angle of repose leads to increase the flow
property.
 In selecting lubricants proper attention must
be given to its compatibility with the drug
agent.
 Example :- Different talc significantly varied
the stability of aspirin.
 Talc with high calcium content & high loss on
ignition was associated with increased aspirin
decomposition.

13. Cont…
 Example :- Magnesium stearate is one of the
most widely used lubricants but due to its
hydrophobic properties, it retards the
disintegration & dissolution.
 To overcome the water proofing, sodium lauryl
sulfate is used.

14. Types of Lubricants
1) Intrinsic Lubrication.
2) Extrinsic lubrication.

15. Intrinsic Lubrication
 In this method lubricants like magnesium,
calcium, zinc salts of stearic acid are directly
added to granulation, mix & then compress.
 This is the most efficient & most commonly
used method.

16. Extrinsic Lubrication
 In this method, lubricants are directly apply to
the tablet tool surface.
 The melted wax is sprayed to the tool surface,
after one tablet is ejected & before the
granulation for the next tablet enters the die
cavity.

17. Commonly used Lubricants
 Talc
 Magnesium stearate
 Calcium stearate
 Stearic acid
 Hydrogenated vegetable oil.
 Polyethylene glycol

18. Film formation of Lubricants
during mixing
 When a powdered lubricant is added to a
tableting blend & submitted to a mixing action
it is distributed as free fraction.
 Prolonged mixing time will transfer more
lubricant from free fraction to the surface film.
 The phenomenon of decrease in strength with
an increase mixing time of tablet ingredients
with lubricants is caused by formation of this
lubricant film, which interfere with the binding
of the particles.

19. Film formation of Lubricant on the
Host particle.

20. Cont…
 The crushing strength has been attributed to
weaker bonds after compression between
lubricant – lubricant molecules rather than
strong excipients bonds.

21. Cont…
 Material Type Conc In Granule s
 w/wBoric Acid E,L 1-5Collodial E,G 0.1-
0.5SilicaMagnesium E,L,I 0.1-1SterateStearic
Acid E,I,L 0.1-2Talc E,G 1-5
Material Type Conc In
Granules
w/w
Boric Acid E,L 1-5
Colloidal,
Silica
E,G 0.1- 0.5
Magnesium stearate E,L,I 0.1-1
Stearic Acid E,I,L 0.1-2
Talc E,G 1-5

22. Particle size
 Decrease in particle size, increases the
strength of tablets.
 The powder should posses good flow property
to have uniformity of weight of the tablet.

23. Cont…
The flow property of powder depends upon:-
 Particle size
 Particle shape
 Porosity
 Density
 Moisture of the powder
The rate of flow ∝ Size of particles of
powder

24. Cont…
 As the particle size increases ,there is an
influence of gravitational force on particles
leading to the increase in flow property of
powder.
 Beyond particular point, flow properties
decrease as the particle size increases i.e..
Beyond 10 µm.
 This is due to
 Vander waals forces
 Electrostatic forces
 Surface tension forces
 Mechanical forces

25. Examples
 Decrease in particle size of sodium chloride
results in increase in strength of tablet.
 But with aspirin decrease in particle size
results in decrease in strength of tablet

26. Cont…
 Generally particles with optimum size will give
good strength for tablets.
 If the particle size is large(200-250µm)then
they have a tendency to flow better than the
smaller particles because they have greater
mass.

27. Effect of particle size
 Smaller particles have larger surface area &
when these are expose to atmosphere may
prone to oxidation, moisture adsorption take
place which effect the strength of tablet.
 Very large particles often exist as
agglomerates of a small crystals on
compression these agglomerates breakdown
into small units.

28. Effect of particle size
 Smaller particles may create mixing problems
because surface area is more & may give rise
to strong electrostatic forces as a result of
processing and or Inter-particulate friction
from movement. These may prevent the
desired distribution of these smaller particles.
 As the particle size approaches 10µ & below
weak polarsing electrical forces called vandar
waals force or cohesive forces affect the flow
of powder.

29. Particle shape
 Particle shape also affects the strength of tablet.
 Generally spherical shape is considered ideal for
the tablet, because spherical shape increases the
bulk density.
 Particle shape affects the inter particle friction &
consequently the flow properties of the powder.
 It also affects the angle of repose of powder with
low magnitude surface forces such as particles
greater than 100µm

30.  Particle shape Effect on powder flow 1) Spherical
Flow easily 2) Oblong with smooth edges
Normally flows easily 3) Equidimentional with
sharp edges like cube Does not flow as radially as
1 or 2 4) Irregular shape interlocking particle Poor
flow & bridges easily 5) Irregular shape with two
dimensional particles such as flakes Poor flow &
causes bridging 6) Fibrous particles Very poor
flow & bridges easily
Particle shape Effect on powder flow
Spherical Flow easily
Oblong with smooth edges Normally flows easily
Equidimentional with sharp edges
like cube
Does not flow as radially as 1 or 2
Irregular shape interlocking
particle
Poor flow & bridges easily
Irregular shape with two
dimensional particles such as
flakes
Poor flow & causes bridging
Fibrous particles Very poor flow & bridges easily

31. References
 The Theory and practice of industrial
pharmacy by Leon lachman. Herbert a
Lieberman Joseph kiang third edition.
 Pharmaceutics: The science of dosage form
design by a Michael E. Aulton.
 Remington “The science &practice of
pharmacy volume1,19th edition 1995
 Physical pharmacy By Alfred martin, james
Warrick Varghese Publications.
 www.google.com

32. THANK
YOU!!!!