Moisture Activated Dry Granulation (MADG) was developed in response to the difficulties experienced with wet granulation, in terms of endpoint, drying and milling. Wet granulation process endpoint is very sensitive to granulation time and shear. The wet granules need to be dried to a narrow range of moisture contents, which is difficult. The dried granules need to be milled, but the milled granules often have either too many fines or too many coarse particles (or both) — an undesirable bimodal distribution.
The MADG processMADG has two stages: agglomeration and moisture distribution. Success depends on the selection and order in which the formulation ingredients are added, as well as how the process is carried out.
During agglomeration, a major portion of the formulation containing the drug is agglomerated. The drug is blended with filler and binder in the powder form, and this blend constitutes approximately 50–80% of the formula weight. In the second stage, a small amount (1–4%) of water is sprayed as small droplets onto the blend (while blending). Water moistens the blend and causes the binder to become tacky, which causes particles, particularly fines, to form moist agglomerates. The process does not create large granules, which would need milling, and because very little water is used in the process, the endpoint is not sensitive to blending.
The remaining formula ingredients are then added (while blending), which results in dry and free flowing granulation. Most tablet granulations contain dry binders, such as microcrystalline cellulose, a disintegrant, a lubricant and, quite often, some colloidal silica. These common ingredients are also used in MADG formulations, but are added in a specific order. Following agglomeration, while blending, microcrystalline cellulose is added, which absorbs most of the excess water. Colloidal silica is then added, further absorbing any remaining moisture. If adequate amounts of microcrystalline and silica are used, the granulation at this stage will be dry and free flowing. After this, a disintegrant can be added and blended, followed by the lubricant.
The process only takes about 10–15 min and the final granulation looks like a direct blend formulation with fine particle size distribution. In this process, the drug is bound with the ingredients, as in wet granulation, which minimises the potential for segregation.
In short, MADG has the best attributes of dry blending and wet granulation. However, it must be noted that MADG is not a formula; it is just a simpler process to create granules without heat drying and milling. Granulation and resulting tablet and capsule characteristics will depend on the formula composition. Every formula may not need all of the typical excipients used in the MADG process based formulation; excipients should be selected based on the nature and amount of API and the desired formulation characteristics.
Some of the advantages of MADG include:
In essence, MADG is just a creative form of wet granulation: granules are created with water with the help of granulating material, but no more water is added than necessary. Additionally, because the necessary excipients are already commonly used by the pharma industry there is no conceivable regulatory concern.
There are, however, some drawbacks to MADG: