Spray-dried lactose direct-compression tablet diluents

At about the same time, two materials were introduced that were specifically designed to act as tablet diluents and would not require preliminary treatment. These were spray-dried lactose and microcrystalline cellulose, introduced in 1962 and 1964, respectively. These two substances can be said to have initiated the direct compression revolution. Since that time, a wide range of direct compression tablet diluents has become available. The properties of some of these materials will be reviewed later in this article. 

The first direct compression excipient, spray-dried lactose, was introduced in the early 1960s as a filler specifically designed for direct compression processes. Over many years, more direct compression API and excipients, especially diluents and binders, were developed. Since these are now commercially available, design of direct compression formulations is readily possible. However, despite the simplicity of the direct compression process, the pharmaceutical industry still produces most tablets by wet granulation methods.1... 

A faulty batch of tablets can sometimes be recovered by grinding up the tablets and recompressing them, a process which is known as reworking and is analogous to the dry granulation method of tablet manufacture. This can sometimes cause problems with a direct compression formulation. Many direct compression diluent particles are in the form of aggregates, e.g., spray-dried lactose is composed of small crystals of lactose embedded in amorphous lactose. If these aggregates are compressed, their structure may be broken down to such an extent that subsequent recompression will result in impaired tablet quality. 

Though numerous direct compression diluents are available, none is ideal. For example, spray-dried lactose flows easily but forms relatively weak tablets. 

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