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Wet granulation is the most widely applied procedure to obtain a material with sufficient flowability. Wet granulation has several advantages, such as a lower risk of segregation and fewer requirements with respect to flowability of the excipients.
Generally, granulates are produced in a granulator by mixing the active ingredient, the filler and, if necessary, a disintegration agent, followed by the addition of an aqueous solution of a wet binder. This is processed into a wet mass, followed by sieving, drying and in most cases, sieving again. Granulation may also be carried out in a fluid bed dryer or a spray dryer, resulting in more porous and softer granules. When produced in a granulator, a hard granulate with low porosity is obtained. Nowadays, pellets are also produced using a granulator.
The hardness and porosity of the material are a matter of balance. Granules that are too porous may still show too poor a flowability. Granules that are too hard generally show capping problems during tabletting.
Milled lactose products are extremely useful for wet granulation processes. Standard products on the market, such as Lactochem Fine Powder, have a particle size distribution suitable for about 80% of the wet granulation applications. Sometimes, a larger surface area is needed in the formulation. This is supplied by extremely strongly milled lactose, as is also needed for pellets produced by wet granulation. The gently milled lactose types are more appropriate for soft granules.
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