Wet granulation technique is often employed in the preparation of free flowing agglomerates. It is essential that the agglomerates/granules produced were suitably dried prior to further processing such as tabletting, capsule or sachet filling. The drying process can have an impact on the final properties of granules and it has been reported that solute migration, overheating and structural damages of granules were not uncommon in conventional drying methods. 1,2) Often, the properties of the granules have been found to influence the quality of the final product.3-5) Thus, it is crucial that the drying method be controlled to assure that it does not adversely affect the quality of the final product.Common drying methods used in the pharmaceutical industry include hot air oven drying and fluid bed drying. These methods employ different modes of moisture removal and differ in drying capability. In recent years, microwave drying has gained greater interest. The moist material is subjected to the high frequency electromagnetic waves that selectively excite the polar molecules (dipoles) and ions causing them to align with the rapidly alternating electric field. Heat (dielectric heating) will be generated during the orientation of these dipoles and ions that in turn evaporates the moisture present in the material. Thus, a pressure gradient is created and it promotes the rapid removal of liquid water and water vapour towards the surface of the material.6-9) Basically, the principle of dielectric heating involves the absorption of energy by dipoles and the energy absorbed is given by:where P ϭenergy absorbed f ϭmicrowave frequency E ϭelectric field E 0 ϭdielectric constant of vacuum E r ϭdielectric constant of material tan dϭloss tangent tan d can be regarded as a measure of the molecular interaction. The product of the dielectric constant, E r and tan d is the loss factor and it determines the energy absorbed and thus the heating rate. McLoughlin and other coworkers found that the moisture content variation within the material undergoing drying with microwave was lower than a conventionally dried product. 8) Thus, microwave drying is especially useful for moisture-sensitive materials.In addition, the microwave drying technology is useful for production of very high potency dosage forms because it provides the possibility of drying in the same production container. Thus, it reduces the likelihood of cross contamination and human contact with the high potency drug. Furthermore, such a single-pot process also reduces the number of equipment used for production and its associated cleaning and validation activities.Various authors have investigated the influence of equipment parameters and the effects of dielectric properties of materials in microwave drying. 8,10,11) It was reported that localised heating could arise in microwave drying and be overcome with bed agitation. With respect to the influence on granular properties, Mandal found that microwave radiation did not modify the surface properties and dissolution rates of...

Roller compaction of a milled botanical (Baphicacanthus cusia) with and without a binder, polyvinylpyrrolidone (PVP) was conducted. Effects of co-milling on binder function and flowability of the powder blend was also investigated. Flakes were comminuted, and the size and size distribution, friability, Hausner ratio, and Carr index of the granulations were determined. Crude herb should be reduced to a suitable size for it to be successfully roller compacted. Larger-sized and less friable granules were obtained with decreasing roller speed. Addition of PVP affected the flowability and binding capacity of the herbal powder blend, which influenced size and friability of the granules. Co-milling of PVP with the herbal powder enhanced the flow of the blends and the effectiveness of the binder, which contributed favorably to the roller-compacted product. Roller compaction is a convenient and cost-effective granulating technique suitable for milled botanicals. Co-milling can be used to improve the properties of roller-compacted products.