Pharmaceutical manufacturing

While a laboratory may use dry ice as a cooling agent for reaction selectivity, this process gets complicated on an industrial scale. The cost to cool a typical reactor to this temperature is large, and the viscosity of the reagents typically also increases as the temperature lowers, leading to difficult mixing. This results in added costs to stir harder and replace parts more often, or it results in a non-homogeneous reaction. Finally, lower temperatures can result in crusting of reagents, intermediates, and byproducts to the reaction vessel over time, which will impact the purity of the product.[1]

Different stoichiometric ratios of reagents can result in different ratios of products formed. On the industrial scale, adding a large amount of reagent A to reagent B may take time. During this, the reagent A that is added is exposed to a much higher stoichiometric amount of reagent B until it is all added, and this imbalance can lead to reagent A prematurely reacting, and subsequent products to also react with the huge excess of reagent B.[1]

Whether to add organic solvent into aqueous solvent, or vice versa, becomes important on the industrial scale. Depending on your solvents, emulsions can form, and the time for your layers to separate can be extended if the mixing between solvents is not optimal. When adding organic solvent to aqueous, stoichiometry must be considered again as the excess of water could hydrolyze organic compounds in only mildly acid base conditions. In an even wider scope, the location of your chemical plant can play a role in the ambient temperature of your reaction vessel. A difference of even a couple of degrees can yield much different levels of extractions between plants located across countries.[1]

In continuous manufacturing, input raw materials and energy are fed into the system at a constant rate, and at the same time, a constant extraction of output products is achieved. The process performance is heavily dependent on stability of the material flowrate. For powder-based continuous processes, it is critical to feed powders consistently and accurately into subsequent unit operations of the process line, as feeding is typically the first unit operation.[2] Feeders have been designed to achieve performance reliability, feed rate accuracy, and minimal disturbances. Accurate and consistent delivery of materials by well-designed feeders ensures overall process stability. Loss-in-weight (LIW) feeders are selected for pharmaceutical manufacturing. Loss-in-weight (LIW) feeders control material dispensing by weight at a precise rate, and are often selected to minimize the flowrate variability that is caused by change of fill level and material bulk density. Importantly, feeding performance is strongly dependent on powder flow properties.[3][4]

In the pharmaceutical industry, a wide range of excipients may be blended together with the active pharmaceutical ingredient to create the final blend used to manufacture the solid dosage form. The range of materials that may be blended (excipients, API), presents a number of variables which must be addressed to achieve target product quality attributes. These variables may include the particle size distribution (including aggregates or lumps of material), particle shape (spheres, rods, cubes, plates, and irregular), presence of moisture (or other volatile compounds), particle surface properties (roughness, cohesion), and powder flow properties.[5]

During the drug manufacturing process, milling is often required in order to reduce the average particle size in a drug powder. There are a number of reasons for this, including increasing homogeneity and dosage uniformity, increasing bioavailability, and increasing the solubility of the drug compound.[6] In some cases, repeated powder blending followed by milling is conducted to improve the manufacturability of the blends.

In general, there are two types of granulation: wet granulation and dry granulation. Granulation can be thought of as the opposite of milling; it is the process by which small particles are bound together to form larger particles, called granules. Granulation is used for several reasons. Granulation prevents the "demixing" of components in the mixture, by creating a granule which contains all of the components in their required proportions, improves flow characteristics of powders (because small particles do not flow well), and improves compaction properties for tablet formation.[7]

Hot melt extrusion is utilized in pharmaceutical solid oral dose processing to enable delivery of drugs with poor solubility and bioavailability. Hot melt extrusion has been shown to molecularly disperse poorly soluble drugs in a polymer carrier increasing dissolution rates and bioavailability. The process involves the application of heat, pressure and agitation to mix materials together and 'extrude' them through a die. Twin-screw high shear extruders blend materials and simultaneously break up particles. The resulting particles can be blended and compressed into tablets or filled into capsules.[8]