Now a days direct compression technique has been one of the well-accepted methods of tablet manufacture. An extensive range of materials from various sources have been developed and marketed as directly compressible diluents such as lactose, starch, cellulose derivatives, inorganic substance, polyalcohols, and sugar-based materials.
Major limitation of co-processed excipient mixture is that the ratio of the excipients in a mixture is fixed and in developing a new formulation, a fixed ratio of the excipients may not be an optimum choice for the API and the dose per tablet under development .
In addition to the development of directly compressible excipients by modifying just a single substance, co-processing of two or more components has been applied to produce composite particles or co-processed excipients. The composite particles or co-processed excipients are introduced in order to provide better tableting properties than a single substance or the physical mixture.
List of Co-Processed Excipients Used To Achieve Better Tableting Properties
Nu-Tab is a roller compacted granulated product consisting of sucrose, invert sugar, cornstarch and magnesium stearate. It has better flowability due to relatively larger particles but has poor colour stability compared to other directly compressible sucrose and lactose. It is primarily used for preparation of chewable tablets by direct compression.
Di-Pac is a directly compressible, co-crystallized sugar consisting of 97% sucrose and 3% modified dextrin (5). It is a free flowing, agglomerated product consisting of hundreds of small sucrose crystals glued together by the highly modified dextrin. At high moisture level, Di-pac begins to cake and loose its fluidity. Tablets containing a high proportion of Di-pac tend to harden after compression at higher relative humidity. Its sweet taste makes it suitable for most directly compressible chewable tablets.
Emdex and Maltrin
Emdex is produced by hydrolysis of starch and consists of aggregates of dextrose microcrystals intermixed and cohered with a small quantity of higher molecular weight sugars. Emdex occurs as white, free flowing, porous spheres which are water soluble and non-hygroscopic. Emdex is generally used in directly compressible chewable tablets because of its sweet taste. It has good binding properties and slight lubricant sensitivity. It exhibits high moisture sensitivity, at room temperature and at 50% RH, the crushing strength of tablets decreases dramatically, whereas during storage at 85% RH tablets liquefy.
Ludipress, a co-processed product, consists of 93.4% a-lactose monohydrate, 3.2% polyvinyl pyrrolidone (Kollidon 30) and 3.4% crospovidone (Kollidon CL). It consists of lactose powder coated with polyvinyl pyrrolidone and crospovidone. Although, Ludipress contains disintegrant, the disintegration of tablets takes longer than tablets containing α-lactose monohydrate, Tablettose and anhydrous b-lactose. At low compression force Ludipress gives harder tablets but the addition of glidant and disintegrant is needed. It is reported that binding capacity of Ludipress was higher than that of microcrystalline cellulose.
Cellactose is a co-processed product consisting a-lactose monohydrate (75%) and cellulose (25%). Apart from good flowability, it has good compactibility. The compactibility is attributed to a synergetic effect of consolidation by fragmentation of lactose and plastic deformation of cellulose. Because the lactose covers the cellulose fibers, moisture sorption is much lower than that of microcrystalline cellulose alone. Aufmuth et al reported that the Cellactose exhibited increased crushing strength of the compacts along with reduced friability and lower disintegration time than the dry blend of lactose and cellulose. Armstrong et al. pointed that Cellactose exhibit the dual consolidation behaviour since it contains a fragmenting component (lactose) and a substance that consolidates primarily by plastic deformation (Cellulose).
Pharmatose DCL 40
It is a co-processed product consisting of 95% b-lactose and 5% anhydrous lactitol. Due to spherical shape and favourable particle size, it exhibits good flowability. It has high dilution potential than other lactose based products due to better binding property. It has very low water uptake at high humidity.
It is co-processed silicified microcrystalline cellulose. It consists of 98% microcrystalline cellulose and 2% colloidal silicone dioxide. The manufacturer claim better flowability and compressibility compared to Emcocel and Avicel PH 101 or physical mixture of MCC with colloidal silicone dioxide. Prosolv containing tablets were significantly robust than those produced from regular cellulose by wet granulation. In the presence of magnesium stearate (0.5 %), tablets prepared with Prosolv maintained tensile strength profiles, whereas the tensile strength of regular cellulose was significantly affected.
Starlac is a co-processed excipient consists of lactose monohydrate and maize starch produced by spray drying. The advantage of Starlac are its good flowability depending on the spray-drying process, an acceptable crushing force due to its lactose content, its rapid disintegration depending on starch .