Lubricants used in pharmaceutical industry

Lubricants are the most important excipients which are used for the manufacturing of oral solid dosage forms in pharmaceutical industries.Lubricants are used to reduce friction between machine parts and the product to make the process smooth.If lubricants are not present in the formulation then sticking, picking like problems may occur and it results in decreased efficiency of the compression, encapsulation and dry powder filling machines.

Coast of operation is also increased due to wastage of time, so a good lubricant is selected to overcome these problems.In this article we will discuss working of lubricants,their effective concentration for use,types of lubricants either hydrophilic or hydrophobic,effect of over lubrication and importance of blending time with lubricants.

Mechanism of Lubricants

There are four mechanisms of lubrication

• Hydrodynamics lubrication
• Elastohydrodynamic lubrication
• Mixed Lubrication
• Boundary lubrication

First three are usually for liquid lubricants and forth one mechanism that is boundary lubrication is involved in the lubricants used for oral solid dosage forms.

Lubricants used for oral solid dosage form are in the form of fine powders. They form a layer around granules and reduce friction between machine parts and the product.

Characteristics of Good Lubricant.

A good lubricant usually has the following three main characteristics.

True Lubricant Role 

Lubricants having a true lubricant role reduce friction between die walls and tablets formed during ejection.

Glidant Effect

A good lubricant also has a glidant effect meaning it reduces friction between particles and increases flow.

Anti Adherent Effect

A good lubricant must have an anti-adherent effect meaning it should prevent sticking of the product to punch face in case of compression machine and to tamping pins in case of encapsulation machine.

Also Read: 

Pharmaceutical Questions and Answers.

Potency calculation of Active pharmaceutical Ingredient.

Properties of a Good Lubricant.

• It should be inert.
• It should be effective in low concentration.
• Should form a layer around granules to give a good lubricating effect.

Types of Lubricant

There are two types of lubricant 

1. Hydrophobic Lubricants
2. Hydrophilic Lubricants

1.0 Hydrophobic Lubricants

• Hydrophobic lubricants are insoluble in water.
• Hydrophobic lubricants are lipophilic.
• These are most commonly used lubricants because they are most effective to reduce sticking and picking.
• They are effective in low concentration.
• Hydrophobic lubricants have all three main characteristics meaning true lubricant role, anti-adherent and glidant effects.
• The mixing time and concentration of Hydrophobic lubricants should be adjusted carefully.
• Increased blending time or higher concentration of Hydrophobic lubricants results in following tablet defects
  • Prolonged Disintegration Time.
    • Retard Dissolution.
    • Reduce Compaction
    • Low Hardness
    • Tablet capping

Prolonged Disintegration Time & Retard Dissolution.

When higher concentrations of hydrophobic lubricants are used or when blending time with hydrophobic lubricants is increased the covering formed around lubricant becomes strong and it repels water so disintegration time is increased and dissolution profile is decreased.

Reduce Compaction, Low Hardness & Tablet capping

When the coverings formed by hydrophobic lubricants becomes strong it results in slippery surfaces of granules due to lipophilic covering.It may results in decreased compaction properties because when we apply pressure to compress the granules or powders the surfaces slip and proper hardness is not achieved, this may also result in tablet capping.

Solution

• Blending time with hydrophobic lubricants should not be prolonged.
• It should be  3-5 minutes.
• The concentration of hydrophobic lubricants should be optimum.

Also Read: 

Lux level for Different areas in pharma. 

Examples of Hydrophobic lubricants

Following are some main examples of hydrophobic lubricants.

Metal salts of Fatty Acids

These are as follow,

• Magnesium Stearate
• Calcium Stearate 
• Zinc Stearate

In this category, Magnesium stearate is most important and is the most widely used lubricant.

Fatty Acid

It includes the following

• Myristic Acid
• Palmitic Acid
• Stearic acid

Fatty Acid Esters

Inorganic Materials

It includes following 

• Talc

Magnesium Stearate

Magnesium Stearate is a hydrophobic lubricant and is insoluble in water.

It is also known as die wall lubricant and it is the most widely used lubricant in pharma industries for manufacturing of 

tablets,capsules, dry powder suspensions and sachets.

It is effective in low concentration.

Concentration of Magnesium Stearate

The recommended concentration of Mg stearate as the lubricant is 0.25-5%.

 (Ref Handbook of pharmaceutical excipients.)

Appearance

• It is fine white powder with faint odour.
•  It has low bulk density.
•  It adheres to the skin.
•  One common identification test for Mg stearate is that it fills the pores of fingers in a very fine and smooth way and it can not be removed or cleaned from pores by rubbing it.

Precautions for Mg Stearate

• Always use a mask and gloves to use mg stearate. 
• It may cause respiratory problems so always wear a mask.

Incompatibility

Mg Stearate is incompatible with following,

• Strong Acid
• Iron Salts
• Alkalis
• Aspirin
• Few vitamins

It is also practically observed that we do not use the Mg stearate in the products containing aspirin and instead of Magnesium Stearate we use talc or talcum.

Talcum

• Talc is also known as talcum.
• It is a naturally occurring mineral.
• It is insoluble in water and is a hydrophobic lubricant.
• It is used in products where we can not use Mg stearate like in aspirin formulations.

Apart from using as a lubricant,talc is also used as 

• Glidant
• Diluent
• Dusting powder
• In Controlled release product to retard dissolution

Concentration of Talc

Stearic Acid

• It is used as a lubricant in tablets and capsules.
• It is also used as a binder.
• It is insoluble in water.

Concentrations of Stearic Acid

It is used as lubricant in tablet in concentration of 1-3%

Palmitic Acid

• Palmitic acid is used as a lubricant for manufacturing of tablets and capsules.
• It is insoluble in water.

Myristic Acid

• Myristic acid is used as a lubricant for manufacturing of tablets and capsules.
• It is insoluble in water.

2.0 Hydrophilic Lubricants

• Hydrophilic lubricants are water-loving.
• Hydrophilic lubricants are not as good lubricants as hydrophobic lubricants.
• They do not possess an anti-adherent and glidant effect.
• The layer formed by hydrophilic lubricants is not too strong so it does not affect the disintegration and dissolution profile of the product.

Examples of Hydrophilic Lubricants

Following are some examples of hydrophilic lubricants

• Sodium Stearyl Fumarate
• Sodium Lauryl Sulphate
• Magnesium lauryl sulphate
• Sodium Benzoate
• Polyethylene Glycol

Sodium Stearyl Fumarate

• Sodium stearyl fumarate is less hydrophobic lubricant.
• Layers formed by Sodium stearyl fumarate do not affect product disintegration and dissolution profile.
• Sodium stearyl fumarate is used as a lubricant during manufacturing of  tablets and capsules.

Concentration of Sodium Stearyl Fumarate

It is used as a lubricant for tablet and capsules in a concentration of 0.5-2.0%

Sodium Lauryl Sulphate

• Sodium lauryl sulphate is commonly known as SLS.
• It is a surfactant and is used as a tablet and capsule lubricant.
• It should be used with great care because it may cause irritation to the following,
  • Skin
  • Eyes
  • Respiratory Tract
  • Stomach

Concentration of SLS

SLS is used as a lubricant in concentration of  1-2%.

Sodium Benzoate

• It is a water soluble lubricant.
• Sodium benzoate is used as a lubricant for manufacturing of tablets and capsules.

Polyethylene Glycol

• It has different grades.
• It is water-soluble.
• it is used as a lubricant.

Advantages of Lubricant

• Lubricants eliminate sticking and picking.
• Lubricants make the compression process smooth.
• Lubricants make the encapsulation process smooth.
• Make sachet or dry powder filling operations smooth.
• Reduce the cost of operation due to a smooth process.
• Enhance machine efficiency.
• Save time.

Important Note:

• Lubricants are more effective when their surface area is increased.
• Sieving of lubricants increases their surface area.
• Always use lubricants after sieving.
• Do not mix lubricants with other excipients for sieving.
• Do not mix lubricants with other excipients for blending.
• Add lubricants at the end, when blending with all other excipients is completed.
• Blending time should be minimum.

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