Tablet Lubricants , Antiadherents, and Glidants

Sponsored Links

Tablet Lubricants ,Antiadherents, and  Glidants

1.5.5 Antifrictional Agents

What will you gain?

1.5.5.1 Lubricants

1.5.5.1.1 Classification of lubricants

1.5.5.1.1.1 Water Insoluble Lubricants

1.5.5.1.1.2 Water Soluble Lubricants

1.5.5.2 Antiadherents

1.5.5.3 Glidants

1.5.5.1 Lubricants(4,16)

Lubricants are the agents that act by reducing friction by interposing an intermediate layer between the tablet constituents and the die wall during compression and ejection. Solid lubricants, act by boundary mechanism, results from the adherence of the polar portions of molecules with long carbon chains to the metal surfaces to the die wall. Magnesium stearate is an example of boundary lubricant. Other is hydrodynamic mechanism i.e. fluid lubrication where two moving surfaces are separated by a finite and continuous layer of fluid lubricant. Since adherence of solid lubricants to the die wall is more than that of fluid lubricants, solid lubricants are more effective and more frequently used.

Since primarily lubricants are required to act at the tooling or material interface, lubricants should be incorporated in the final mixing step, after granulation is complete. When hydrophobic lubricants are added to a granulation, they form a coat around the individual particles (granules), which may cause an increase in the disintegration time and a decrease in the drug dissolution rate. Presence of lubricants may results in a less cohesive and mechanically weaker tablet because it may interfere with the particle - particle bonding.

Surface area is important parameter for deciding lubricant efficiency. Lubricants with high surface area are more sensitive to changes in mixing time than lubricant with low surface area. Therefore lubricant mixing time should be kept minimum.

Tooling used to compress the tablet is important for deciding type and level of lubricant used. Additional lubricant is often added to the tablet formulations that are to be compressed with curved face punches.

Further, the amount of lubricant increases as the particle size of the granulation decreases but its concentration should not exceed to 1% for producing maximum flow rate.

Lack of adequate lubrication produces binding which can results in tablet machine strain and can lead to damage of lower punch heads, lower cam track, die seats and the tooling itself. And it may also yield tablets with scratched edges and are often fractured at the top edges. With excessive binding the tablet may be cracked and fragmented by ejection.

1.5.5.1.1 Classification of lubricants

Lubricant are classified according to their water solubility i.e. water insoluble and water soluble. Selection of lubricant is depends partly on mode of administration, type of tablet, desired disintegration and dissolution properties, physicochemical properties of granules or powder and cost.

1.5.5.1.1.1 Water Insoluble Lubricants

Water insoluble lubricants are most effective and used at reduced concentration than water soluble lubricants. Since these lubricants function by coating , their effectiveness is related with their surface area, extent of particle size reduction, time, procedure of addition and length of mixing.

Table.17. List Of Insoluble Lubricants

INSOLUBLE LUBRICANTS

CONCENTRATION

COMMENTS

Stearates(Magnesium Stearate, Calcium Stearate, Sodium stearate)

0.25 -1

Reduce tablet strength; prolong disintegration; widely used.

Talc

1 -2

Insoluble but not hydrophobic; moderately effective.

Sterotex

0.25 - 1

-

Waxes

1 - 5

-

Stearowet

1 - 5

-

Glyceryl behapate(Compritol(r)888)

1 - 5

Both lubricant and binder;

Liquid paraffin

Up to 5

Dispersion problem; inferior to stearates

1.5.5.1.1.2 Water Soluble Lubricants

Water Soluble Lubricants are used when a tablet is completely soluble or when unique disintegration and dissolution characteristics are required. Tablet containing soluble lubricant shows higher dissolution rate than tablet with insoluble lubricants. Physical mixture of this lubricant i.e. SLS or MLS with stearates can lead to the best compromise in terms of lubricity, tablet strength and disintegration.

Table.18. List Of Soluble Lubricants

WATER SOLUBLE LUBRICANTS

CONCENTRATION RANGE (%W/W)

Boric acid

1

Sodium benzoate

5

Sodium oleate

5

Sodium acetate

5

Sodium Lauryl sulfate (SLS)

1 - 5

Magnesium lauryl sulfate (MLS)

1 - 2

1.5.5.2 Antiadherents (4, 16)

Some material have strong adhesive properties towards the metal of punches and dies or the tablet formulation containing excessive moisture which has tendency to result in picking and sticking problem. Therefore antiadherents are added, which prevent sticking to punches and die walls.

Talc, magnesium stearate and corn starch have excellent antiadherent properties. Vegan had suggested that silicon oil can be used as antiadherent.

Table.19. List Of Antiadherents

ANTIADHERENT

RANGE(%W/W)

COMMENT

Talc

1 - 5

Lubricant with excellent antiadherents properties

Cornstarch

3 - 10

Lubricant with excellent antiadherents properties

Colloidal silica

0.1 - 0.5

Does not give satisfactory results due to small surface area. Cab-O-Sil(r) and Syloid(r)

DL-Leucine

3 - 10

Water soluble lubricant; excellent antiadherents properties

Sodium lauryl sulfate

<1

Antiadherents with water soluble lubricant

Stearates

<1

Antiadherents with water insoluble lubricant

1.5.5.3 Glidants (4, 16)

GLIDANTS are added to the formulation to improve the flow properties of the material which is to be fed into the die cavity and aid in particle rearrangement within the die during the early stages of compression. If the flow properties are extremely poor then glidants are ineffective and consideration of force free mechanisms may be necessary. Starch is a popular glidant because it has additional value of disintegrant. Concentration of starch is common up to 10%, but should be limited otherwise it will worsen the flow of material. Talc is a glidant which is superior to starch; its concentration should be limited because it has retardant effect on dissolution-disintegration profile.

Silaceous material like colloidal silica i.e. syloid, pyrogenic silica (0.25%), hydrated sodium silioaluminate (0.75%) are also successfully used to induce flow.

Glidants act by interposing their particles between those of material and lower the overall interparticulate friction of the system by virtue of their reduced adhesive tendencies. Similar to lubricants, they are required at the surface of feed particles and they should be in fine state of division and appropriately incorporated in the mixture.

Key Phrases

O Lubricants are added to reduce the friction during compression.

O Antiadherents avoid sticking to die walls and picking by punches.

O Glidants improve the flow property of material/granules.

About the Author

Dr.Mukesh Gohel's picture
Author: Dr.Mukesh Gohel

Dr. Mukesh Gohel is principal, professor at the LMCP, Ahmedabad served in academics for more than 40 years. He provides training in leading pharmaceutical industries in the areas of Design of Experiments and Quality by Design. His current areas of interest are direct compression and improvement of drug dissolution.

You May Also Like..