Lubricant Concentration For Pharmaceutical Preparations
Lubricants are added to the formulation of drugs reduce friction during processing. Specifically there are three main reasons why pharmaceutical companies use lubricants:
- to enhance the flow of production by reducing friction between particles
- to reduce friction between the surface of the tablet and die wall during ejection, so as to reduces the wear and tear on punches and dies.
- to prevent granules from sticking to the punch faces as well as to the dosator and tamping pins.
Characteristics of a good lubricant:
- have minimal adverse effects on the end product
- have low shear strength (so that the lubricant and not the granules shear during blending)
- be able to form a strong and durable layer over the surface of the tablet
- unaffected by the variables in the process
- chemically inert
Solid lubricants act by a boundary mechanism that is the result of the adherence of the polar portions of molecules with long carbon chains to the metal surfaces of the die wall. Magnesium stearate is an example of a commonly used boundary lubricant for tablets as well as for capsules.
Fluid lubricants, on the other hand, operate by a hydrodynamic mechanism. In this the fluid forms a continuous layer of lubricant between solid particles. Since solid lubricants adhere better to the die walls than fluid lubricants, solid lubricants are more effective and more frequently used.
Since lubricants need to act at the tablet press, they are normally added at the final mixing step, after granulation is complete. When hydrophobic materials, such as magnesium stearate, are added to a granulation, they form a coat around the individual particules (granules), which may cause an increase in disintegration time in the body, even when the product is in the form of a capsule. It has been noted in the case of capsules, that once gastric juices have dissolved the shell, a capsule-shaped plug of ingredients often remains, especially if the capsule has been filled by machine. In the case of a tablet, the presence of lubricants can also result in a less cohesive and mechanically weaker product because the lubricant may reduce the particle-particle bonding. Note that additional lubricant is often added to the tablet formulations that are to be compressed with cured face punches.
Surface area is an important parameter when deciding which lubricant to use. Lubricants with high surface area are more sensitive to changes in mixing time than those with low surface area. Lubricant mixing time should therefore be kept to a minimum. The amount of lubricant added should generally be kept below about 1% by weight for producing the maximum flow rate of powder.
Inadequate lubrication can produce binding in the tablet press, which can lead to damage of lower punch heads, lower cam track, die seats and the tooling itself. It may also produce tablets with scratched edges that are often fractured at the top edges. With excessive binding, the tablet may crack and fragment on ejection.
Classification of lubricants and concentrations required
Lubricants are classified according to their solubility in water. Selection is dependent partly on the method of administration, the type of tablet, desired disintegration and dissolution properties, and the physical and chemical characteristics of the granules or powder, and cost.
1. Water Insoluble Lubricants
Water insoluble lubricants are most effective at low concentration. Since these lubricants coat the granules, their effectiveness is related to the surface area of the particles, and the method of addition and mixing time.
|Magnesium Stearate||0.25 to 5.0%|
|Talcum||1.0 to 10%|
|Steraic acid||1.0 to 3.0%|
|High melting wax||3.0 to 5.0%|
|Maize starch||5.0 to 10.0%|
|Colloidal silicondioxide or Aersol||0.1 to 0.5%|
2. Water Soluble Lubricants
These lubricants are used for tablets that are completely water soluble or when unique disintegration and dissolution characteristics are required. Tablets containing water soluble lubricants show higher dissolution rates than those with insoluble lubricants.
|Sodium benzoate||2.0 to 5.0%|
|Poly ethylene glycol 1000||1.0 to 4.0%|
|Poly ethylene glycol 6000||1.0 to 4.0%|
If you have any questions on the lubricants or flowing agents that you should be using in your pill / tablet mix or pill press, LFA Tablet Presses would be more than happy to help. Simply get in contact with us.