Lubricants and Glidants used in Tablet Formulations

Tablets Lubricants

Lubricants and Glidants used in Tablet Formulations are:

• Magnesium stearate
• Stearic acid
• Sodium stearyl fumarate
• Hydrogenated vegetable oil
• PEG 4000, 6000
• Hexagonal boron nitride
• DL-Leucine
• Sodium lauryl sulfate
• Gliceryl behenate
• Sodium benzoate
• Colloidal silicone dioxide
• Talc
• Starch
• Super disintegrants
• Sodium starch glycolate (Explotab)
• Cross-linked PVP (Polyplasdone XL)
• Cross-linked carboxymethyl cellulose (Ac-Di-Sol)

Pharmaceutical lubricants are materials used in tablet formulations to reduce the friction between the lower punch and the die and the tablet. Friction damages both the tablet and the tablet press during the ejection cycle.

Lubricants are a mechanical necessity, without which modern tablet manufacturing would be impossible. Glidants are materials that reduce interparticular friction, covering the particle surfaces with a thin layer, and as a result helping in better granule flow.

Colloidal silicon dioxide, talc, and starch can be used as glidants; colloidal silicon dioxide is effective as low as 0.5% as a glidant.

Lubricants are added to pharmaceutical granules just before the tableting stage.

Mixing the main granule mass with a lubricant has been an intensively investigated subject. Prolonged mixing with a surface covering lubricant such as magnesium stearate negatively affects the binding capacity of a granule mass. Hence, tablet formation might be inhibited, unless the granule mass undergoes brittle fracture and creates new clean surfaces.

Especially, materials exhibiting plastic deformation with a limited surface area would show a strong sensitivity to lubricants.
Therefore, the specific surface area of a lubricant as well as the surface area of the granule mass are both important parameters in selecting lubricant type, concentration, and mixing times. Boundary lubricants will adhere on the metal surfaces of the tablet press, die, and punches and will form a boundary layer with the tablet.

Alkaline stearates such as magnesium stearate are an example of a boundary lubricant.

Magnesium stearate is still the most effective pharmaceutical lubricant.

Its usual concentration range is between 0.1% and 2%, and its effectiveness shows a biphasic profile, a region of a fast reduction in friction up to 1 %, and a slower friction-reducing effect after 1%. Magnesium stearate reduces not only the lower punch ejection force by about 70% but also tablet tensile strength.

Stearic acid is the second most important lubricant. It is not as effective as magnesium stearate, the
minimum effective stearic acid concentration is about 1%, and it reduces the lower punch
ejection force no more than 30%.

This fatty acid is however useful when an alkaline ingredient in a tablet formula is undesirable.

The hexagonal form of boron nitride (HBN) has been reported as a potential tablet lubricant. HBN is similar to graphite, which is soft and lubricious. This inorganic solid powder retains its ability to lubricate in extreme cold or heat.
It was reported that boron nitride reduced the lower punch ejection force as efficiently as magnesium stearate, but its ability to reduce the tablet tensile strength is less than magnesium stearate. The result is mechanically stronger tablets.

Therefore, there is a good potential for HBN to be used as a tablet lubricant.

For effervescent tablets, water-soluble lubricants are required since insoluble alkaline lubricants would accumulate on the surface of final solution or form a cloudy solution with an alkaline taste, all of which is undesirable.

Sodium lauryl sulfate, DL-leucine, or various PEGs can be used as water-soluble lubricants.
Liquid paraffin and hydrogenated vegetable oil are also among the lubricants, but their effectiveness is lower than that of magnesium stearate and stearic acid.