Lubricant and Glidant are two important excipients in solid dosage manufacturing especially tablets. Typically, these two materials have the overlapping function, thus, sometimes make confusion. The differentiation between these terms lubricant and glidant are as follows:
What is the definition of Lubricant and Glidant?
Lubricant is a non-toxic, pharmacologically inactive substance added to the formulation to decrease friction between tablet’s surface and the die wall cavity in which the tablet was formed and to reduce wear and tear of dies and punches. Probably, it is hard to produce a proper tablet without lubricant. Also, various specialist defines the lubricants as below:
Lubricant is a compound added in tablet formulations primarily to reduce friction between the die wall and granules as the tablet is formed and ejected .
A lubricant may be defined as a suitable material, a small amount of which interposed between two rubbings surfaces will decrease friction arising at the interface [2, 3].
On the other hand, glidant is a non-toxic, pharmacologically inactive substance used to optimize the flow properties of tablet granulation or powder materials by decreasing interparticle friction and cohesion. At a certain range of concentrations, only a glidant may work such as talc 5%. Glidant may inhibit flow properties at above a certain concentration. Moreover, glidant is used in combination with lubricant because they have no ability to reduce die wall friction.
How Lubricant and Glidant works (Mechanism of Action)?
Solid particles surfaces are not smooth, they consist of irregularities known as asperities. When two solid material particles in contact are displaced relative to each other and parallel to the plane of contact, a resistance known as friction. [4, 5]. This friction or asperities may responsible for decreasing flow-ability and interrupting smooth ejection of tablet from the die cavity.
Friction can be reduced by adding a continuous film of lubricants to the moving surfaces or by boundary films. Lubricants produce a film layer in between granules. When the lubricant is thought to offer a lower shear interface than that characteristic of the die wall tablet surfaces and will thus readily shear when tangential motion is initiated between the tablets and die during the ejection process .
Fluid lubrication would help in the easy ejection of a tablet but the tackiness of the tablet and reduction of tablet strength are drawbacks of fluid lubricants. Boundary lubricants are more commonly used over fluid lubricants .
On the other hand, a glidant’s effect is due to a counter-action to factors resulting in poor flowability of powders. Besides, glidant increases powder flow properties by correcting surface irregularity, reducing interparticular friction as well as decreasing surface charge.
Classification of Lubricant and Glidant
Firstly, Based on Solubility, Lubricants are two types:
a) Water soluble
Generally, they are poor lubricants and they have no glidant or anti-adherent properties. For example, Boric acid, Sodium oleate, Sodium Benzoate, Sodium Lauryl Sulphate, Sodium Acetate and Magnesium Lauryl Sulphate, etc.
b) Water insoluble
They are the most widely used lubricants. Generally, they are good lubricants and many of them have both glidant and anti-adherent properties. In addition, they are effective at relatively low concentrations. For example, Calcium stearate, magnesium stearate, Sterotex, Talc, and Sterowet etc.
Secondly, Based on Nature of the materials, Lubricants are 2 types:
Solid: For example, Calcium Stearate, Magnesium Stearate, and Talc etc.
Liquid: For example, liquid paraffin.
On the other hand, Based on Solubility Glidant are two types:
Hydrophobic: For example, hydrophobic silica and hydrophobic colloidal silicon dioxide.
Advantages of Lubricant and Glidant
- Smooth ejection of tablet from die cavity by reducing inter-particle friction.
- Prevent the adhesion of tablet.
- Many lubricants may improve flowability
- Reducing wear on rubbing surfaces .
- High resistance of deterioration in storage
- Highly stable.
- Smooth flow of powder or granules during solid dosage from manufacturing.
- Helps to maintain uniformity of powder mixture of API and/or excipients.
- Indirectly prevent weight variation.
Disadvantages of Lubricant and Glidant
- Careful selection is necessary since some lubricants may interact adversely when in combination; for example, magnesium stearate and talc .
- Lubricant at higher concentration may induce tableting problems such as capping, lamination.
- Some lubricants are the production of oil spots. For example, stearic acid salts and derivatives. .
- Higher coefficient friction.
- Improper mixing of lubricant affect tablet hardness.
- At a certain range of concentrations, only a glidant will work. Above a certain concentration, the glidant will inhibit flow properties.
- Besides, they have no ability to reduce die wall friction.
Mixing Time Range of Lubricant and Glidant
Generally, Lubricant mixing time is too short (2-5 minutes). For example, the most widely used lubricant, Magnesium Stearate is added to the blend for 2-5 minutes prior to the conclusion of the blending period . While Glidant mixing time is higher than lubricant mixing time.
Effect of High Mixing Time of Lubricant and Glidant
Generally, the high mixing time of lubricant may decrease the tablet hardness . On the other hand, high mixing time of glidant does not affect tablet quality except excessive high mixing time. But, the short mixing time of glidant cannot produce good flow ability.
Mixing order of Lubricant and Glidant
Typically, Lubricant is added to the blend prior to the end of the blending period. Simply, it is the last stage of mixing before compression. On the other hand, Glidant is added to the blend prior mixing of lubricants, sometimes, in combination with lubricant. In addition, glidant is added to the first mixing stage in direct compression.
Pharmaceutical applications of Lubricant and Glidant
Applications of Lubricant
- Smooth ejection of tablet from die cavity by reducing inter-particle friction.
- Lubricant may prevent adherence of tablet to the die wall thus no sticking of granules to the tooling.
- Also, Lubricant may improve granules flow properties.
Applications of Glidant
- The most noteworthy application is to improve powder flow properties.
- To reduce the cohesion
- Correcting surface irregularity
- Decreasing surface charge
Example of Lubricant and Glidant
Magnesium stearate and calcium stearate are the most widely used lubricant. Probably, Talc is second most commonly used lubricant but Talc at a 5% concentration used as a glidant . Most commonly used lubricants are :
- Magnesium stearate
- Magnesium silicate
- Calcium stearate
- Stearic acid,
- Talc 
- Sodium Lauryl Sulphate
- Magnesium Lauryl Sulphate
- Corn Starch 5-10%
- Talc 5%
- Colloidal Silica such as Cab-O-Sil, Syloid, or Aerosil in 0.25-3% 
In short, the difference between Lubricant and Glidant
Lubricant is a non-toxic, pharmacologically inactive substance added to the formulation to decrease friction between a tablet’s surface and the die wall cavity in which the tablet was formed and reduce wear and tear of dies and punches.
Glidant is a non-toxic, pharmacologically inactive substance used to optimize the flow properties of tablet granulation or powder materials by decreasing interparticle friction and cohesion.
|Friction can be reduced by adding a continuous film of lubricant to the moving surfaces or by boundary films.||Correcting surface irregularity, reducing interparticular friction and decreasing surface charge.|
|Based on solubility lubricants are two types:
a) Water soluble
b) Water insoluble
Also, based on nature, lubricants are 2 types:
|They have no such establish classification but they are also two types:
Certainly, Glidant are only in solid form.
|a) Smooth ejection of tablet from the die cavity by reducing inter-particle friction.
b) Prevent the adhesion of tablet.
c) Many lubricants may improve flowability
d) Reducing wear on rubbing surfaces
|a) Smooth flow of powder or granules during solid dosage from manufacturing.
b) Helps to maintain uniformity of powder mixture of API and/or excipients.
c) Indirectly prevent weight variation.
|Lubricant at higher concentration may induce tableting problems such as capping, lamination.||At a certain range of concentrations only a glidant will work and they have no ability to reduce die wall friction.|
|Generally, Lubricant mixing time is too short (2-5 minutes).||Glidant mixing time is higher than lubricant mixing time.|
|The high mixing time of lubricant may decrease the tablet hardness.||High mixing time of glidant does not affect tableting quality except excessive high mixing time. But, the short mixing time of glidant cannot produce good flow ability.|
|Typically, Lubricant is added to the blend prior to the end of the blending period.||Glidant is added to the blend prior mixing of lubricants, sometimes, in combination with lubricant. Also, in direct compression, glidant is added to the first mixing stage.|
|To smooth ejection of tablet from die cavity by reducing inter-particle friction.||To improve powder flow|
|Example: Magnesium stearate, Magnesium silicate, Calcium stearate, Stearic acid, and Talc etc.||Example: Colloidal Silica such as Cab-O-Sil, Syloid, or Aerosil in 0.25-3% , Corn Starch 5-10%, and, Talc 5% etc.|
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