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Formulation Excipients of Tablets

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Formulation
Excipients of Tablets

Hello pharma bloggers, in this present blog we shall
have an over look on the formulation ingredients of tablets.

This is blog is aimed to cater the needs of those
pharma fresher graduates who have just completed their graduation and looking
to find their future in the phrama industry rather than higher education. If
you seem to have interest in the production department or quality control
department you need to have a keen knowledge of tablets and capsules.

Our team ASSIMILATORS have
made a small attempt, I hope you all would like this.

Tablet is an solid dosage form which consist of one
or more active ingredient with excipients, excipients are very important part
of the tablet formulation,

Excipients are pharmacologically inactive substances
included in the formulation which is used as a carrier of active ingredient.

In a conventional tablet the excipients used in the
tablet formulation include

1.Diluents/fillers

2Binders

3.Disintegrants

4.Lubricants

5.Glidants

6.Miscellaneous

ODiluents:

Diluents
are used to increase the bulk content of the dosage form, this is done in a
situation where the active constituent to be incorporated in the formulation is
of less quantity. For ex if the active ingredient is just 5 mg, is such a case
a tablet of just 5 mg is very difficult to manufacture and handle too, thus the
bulk content is increased by addition of inactive excipient.

Round tablets of weight 120mg to 700mg and for oval
tablets 800mg are easy to handle

Examples of excipients:

lactose,
lactose anhydrous, lactose spray dried, directly compressible starch,
hydrolyzed starch, MCC, other cellulose derivatives, dibasic calcium phosphate
dihydrate, mannitol, sorbitol, sucrose, calcium sulfate dehydrate, dextrose.

*Most of the excipients are dehydrates,
i.e. contain certain amount of bound water, this bound water is important
during granulation process, it reduces the hygroscopic nature of the
formulation. Making the formulation stable.

*For the active ingredients which are
sensitive to water anhydrous excipients are used like anhydrous lactose or
anhydrous, dibasic calcium phosphate.

*
Spray dried lactose, direct compressible
starch and MCC (avicel) are the diluents that can be used when the formulation
is prepared by direct compression.

*Mannitol is one of the costliest
diluents but it is still used due to the refreshing sensation given by it when
it is used in the chewable tablets.

*Sucrose or sugar based diluents are used
for direct compression formulations. Sucrose based diluents include: Sugartab(
90-93% sucrose+ 7 to 10%invert sugar), Dipac
(97% sucrose + 3% modified dextrin) and Nutab( 95%sucrose+4%invertr sugar with
small amount of corm starch and magnesium stearate)

OBinders:

*These are the dry powders or liquid
which are added during wet granulation to promote granules or to promote
cohesive compact during direct compression.

*It provides mechanical strength to the
tablet.

*Binders can be in powder form and liquid
form example of binders are

Powder
binders: cellulose, methyl cellulose, polyvinyl
pyrrolidine, PEG

Solution
binders: gelatin, PVP, HPMC, PEG, sucrose, starch

*Binders
can be added in the following ways to the formulation

oAdded as powder before wet
agglomerisation so that the binder is evenly distributed.

oAs solution form it is used as
agglomerisation liquid in the wet granulation. It is called as liquid binder

oAs a dry powder, which is mixed with
other ingredients before compaction (slugging or tabletting). It is called as
dry binder.

*Natural binders like acacia and
tragacanth are used in solution form in the concentration of 10-25%, alone or
in combination for wet granulation and they can be added as powder for the
direct compression process.

*Gelatin is used along with acacia or
alone this form a better binding agent than the above two natural polymers.

*Polymers like MC, HPMC are used as dry
powders in case of direct compaction, they act as good binding agents, in the
solution form they act as good adhesives.

*Ethyl cellulose and HPMC can be used in
alcoholic solutions. they act as anhydrous adhesives.

ODisintegrant:

*Disintegrant are added to the
formulation as it breaks the dosage form into smaller particles when it comes
in contact with the liquid, these smaller fragments have greater surface area
which will increase the dissolution of the drug.

*Various mechanism of disintegrations are
proposed:

oBy breaking into fragments: When the
tablet comes in contact with the liquid, the liquid penetrates into the pores
of the tablets and breaks it into fragments. To improve the water uptake into
the pores certain hydrophilic polymers are added to the formulation

oBy swelling: when the tablet comes in
contact with the water it swells and ruptures the tablet into small particles.

*Examples of disintegrants are: starch,
starch derivatives, clay, cellulose, alginates, PVP, cross linked Na CMC

*Starch is used for in the concentration
range of 5 to 20% of the tablet weight

*Modified starch are also used which like
Primogel, Explotab. These are used in the low concentration like 1 to 8%, Pregelatinised
starch is also employed in the formulation with 5% concentration.

*Clay like Veegum HV and Betonite are
used in 10% level,

*Polymers like cross linked PVP, CMC are
also used as disintegrants.

OLubricants:

*Lubricants are used to reduce the friction
between the tablet and die cavity when the tablet die cavity is getting ejected
from the die.

*Lack of lubricant can lead to problems
like capping, scratch on the sides of the tablet, fragmentation of the tablet,
shape out etc...

*Thus to avoid this lubricants are to be
used

*For a lubricant the time of addition,
concentration in which it is to be added and the combination are the important
parameters

oConcentration: as most of the lubricants
are hydrophobic in nature thus the an increased concentration of lubricant
would lead to problems like poor wettability, and dissolution and
disintegration problem this they are added in the concentration less that 1%

oTime of mixing: it is important as over
mixing may lead to reduction in tablet dissolution and disintegration

oCombination: if the lubricant is mixed
with the disintegrant it will lead to formation of an film of lubricant on the
tablet surface which will reduce the disintegration.

*Examples of lubricants are: stearic
acid, stearic acid salt, stearic acid derivatives, talc, PEG, surfactants,
waxes

*Calcium stearate and magnesium stearate
(0.25-0.50%
w/w)
are the most commonly used lubricants followed by talc.

*Higher molecular weight poly ethylene
glycol and certain polymeric surfactants are used as water soluble lubricants.

*Lubrication can be achieved by two ways

oFluid lubrication: it is achieved by the
addition of liquid paraffin which forms an liquid film over the surface, but
this is rarely followed

oBoundary lubrication: in this powder is
mixed to the formulation which forms a film on the surface which reduces the
friction.

*Lubricants can be of two types

oInsoluble lubricants: these are added to
the formulation at the end before the compression of the tablet examples
include: magnesium stearate, stearic acid, glyceryl behnate, glyceryl palmito
stearate,

oSoluble lubricants: these are added to
overcome the defects caused by the insoluble lubricants. Examples include: PEG,
poly oxy ethylene stearate, lauryl sulphate salt

OGlidant:

*Glidants are used to improve the flow
property of the formulation, it reduces the friction between the particles and
between the hopper and particles and die cavity and partices

*Actually glidant, lubricant and
antiadherent have a close relation to each other. They have some functions in
common.

*Most of the glidants used are
hydrophobic thus they are to be carefully added i.e. concentration regulated.

*Examples of glidants are talc, colloidal
silicone dioxide, corn starch.

*Glidants should be of small size so that
they can retain with in the small pores of the granules have a greater surface
area.

OMiscellaneous:

*Above from the above mentioned principal
ingredients following excipients also improve the dosage form characters they
are adsorbents, colouring agents,

OAdsorbent:

*Adsorbents are used when there is an
need to add a liquid or semisolid ingredient in the formulation, adsorbents are
capable of sorbing the liquid component on to the dry powder.

*Thus oil or liquid component can be
incorporated into the powder

*Examples of adsorbents include:
magnesium oxide, kaolin/bentonite,

OFlavorants:

*These are incorporated into the
formulation to improve the flavor or give a pleasant taste to the formulation.

*Flavoring agents are mostly restricted
to the formulations in which are intended to be released in the mouth or
chewable tablets.

*They are usually added in along with the
granules.

OColourants:

*Colouranats are added to the formulation
in order to increase the patent compliance or for identification of the
formulation.

*Usually the colurants are added in the
form of insoluble powder or in the form as liquid in the granulation liquid.

*Examples of colorants are: FD&C and
D &C dyes and lakes.

All
the above excipients described above can be seen in an conventional tablet.

Other
type of tablets also contain the same formulation ingredients but with a few
variation in composition.

Formulation
variables in different types of tablets:

1.Enteric
coated tablet:

*Enteric coated tablets are intended to
be insoluble in the stomach ph and get solublized in the intestinal ph.

*Thus for this purpose in the formulation
of enteric coated tablets polymers like cellulose acetate phthalate, polyvinyl
acetyl phthalate, HPMC phthalate are used

*All the above polymers contain a
dicarboxylic group and phthalic acid in the partly esterifies form. These acid
esters remain insoluble in the acidic ph below 4 and they get hydrated in the ph
range of 4 to 6 i.e. in duodenum, when the drug molecule enters into the intestines
where the ph is in the range of 7 to 8 where these polymers get ionized, and
the ester bonds between them is broken by the esterase present in the intestinal
fluid.

2.Film
coated :

*Film coating is applied to the tablets
to give a smooth finish to the tablets and to protect the tablet from the
external atmospheric conditions

*For film coating a material containing a
plasticizer and a surfactant (for even spreading) is used.

*Examples of polymers used for enteric
coating are hydroxyl propyl cellulose, HPMC.

3.Effervescent
tablets:

*These tablets are intended to produce effervescence
when they come in contact with the water or liquid.

*Thus the formulation of these tablets
includes organic acid and bicarbonates.

*Water soluble lubricants are preferred
here

*Binders are not included in the formulation
or rather a very less concentration is employed.

*Effervescent tablets are prepared by the
direct compression or by compaction of the granules; wet granulation method is
very seldom used.