One fascinating and somewhat rare aspect of tablet manufacturing is the usage of external spray lubricant systems.  Let’s take a look at some of the promise and pitfalls associated with this technology. 

In traditional tablet production, a small amount (between 0.25% and 2%) of lubricant is blended into the formulation to reduce the friction generated during tablet ejection and ejection force while helping to prevent sticking and other tablet defects.  Formulators typically try to minimize the amount of lubricant since it can increase disintegration / dissolution times and reduce tablet tensile strength.

All of the benefits the lubricant provides to making tablets occurs at the tablet surface while the disadvantages occur within the tablet’s interior.

An external spray lubricant system allows the formulator to reduce (or eliminate) lubricants from the blend recipe, improving disintegration / dissolution rates and increasing tablet tensile strength.  Since only surfaces are being sprayed, substantially less lubricant overall is needed. 

Effervescent tablets are the most common product that use external spray lubricant systems since Magnesium Stearate will leave a film residue in the water after a tablet dissolves in water.  ODT (orally disintegrating tablets) are another dosage form that can be well suited to be manufactured with an external spray lubricant system. 

They save money on the cost of your excipients and improve tablet quality, so why are they rare?

First, it isn’t cheap to buy these systems (if it was cheap, you likely wouldn’t want it).  Magnesium stearate, by itself, has poor flowability so the spray system must be able to accurately meter a difficult product.  The spray must be consistent to maintain tablet content uniformity even at low spray rates of 3 to 30 grams per minute.  Preferably, this requires the system to measure by mass flow (weight per time), also known as a gravimetric loss-in-weight.  Coperion’s K-Tron units are a good example of this technology.

Second, it often requires re-validation of a formulation.  Products are typically developed and filed with lubrication in the powder blend.  As every tablet manufacturer for pharma knows, validation is a costly and time-consuming process.  The validation of an external spray lubricant system can be challenging since proving the tablet content uniformity is based on comparing flow rates to tablet output.   

The first step in identifying whether the product requires external spray lubricant technology are good material characteristic studies such as USP <1174>, USP<616>, and USP <1062>. 

Natoli Scientific offers these and more.  Oftentimes, other solutions may be recommended based on the application.  For more information or help, please contact us at Natoli Engineering.