In the classification of drugs, solid preparation is as important as is familiar to us. During preparation, excipients are necessary. They can play a role in drug quality. And among excipients, lubricant, although is not so important, still have their own special role.
For example, during mixing, rolling (dry granulation), tablet pressing and capsule filling, lubricant can decrease friction between equipment surface and solid material surface and guarantee continuous production. And a little amount of lubricant (normally 0.25%-5.0%) can reach the both goals. In addition, it can even improve powder fluidity and help unit operation.
Actually, in practical production, many failures are caused by lubrication or related problems. However, lubrication is still not paid enough attention to as it should be in drug development. In fact, granule properties of lubricant have great influence on the performance of lubrication formula. Studying the influence can help drug producers to better improve quality of solids. Specifically, the most important feature among granule properties of lubricant must be the granularity. But what influence it can have?
As for granularity distribution, researchers find that smaller granule size of lubricant can generate larger cohesion among material granules and then increase porosity of tablets, which will further make powder rearrange and increase the surface area. The larger the specific surface area is, the more uniform powders can be mixed. At last, interaction among material granules, as well as tablet intensity, is obviously strengthened. 
Although reduction of granularity can bring some advantages, additional useless fine granules’ mixing in will also lead to adhesion. These granules can contaminate inner mold surface and form unnecessary film, while adhesion can lead to compressed tablets clogging in the mold. Therefore, operators should pay attention to granularity distribution for target tablet hardness.
In a latest study, researchers surveyed the influence of magnesium stearate lubricant of different granularity and concentration on tablet properties. It is found that the concentration plays a part in controlling tablet hardness at the best (about 18KPa). Besides, researchers also get the result that the most proper lubricant size can avoid material granule separation, reduce weight change during pressing and at the end improve products’ hardness and appearance. 
