Powders and granules

Powders and granules

Introduction

Almost all the pharmaceutical dosage forms involve the handling of powders at one or more stages of their preparation. For example, the manufacture of tablets and capsules requires the compression or filling of powders in a tableting or a capsule filling machine, respectively. Most of the drugs are in solid state at room temperature. Therefore, even the processing of liquid dosage forms, such as oral, ophthalmic, or parenteral solutions, requires the powder drug to be dissolved in a solvent during their manufacture.

In many cases, pharmaceutical powders are dispensed as a dosage form. For example, the lyophilized powders of protein and peptide drugs are provided in a vial for reconstitution before parenteral administration. Similarly, powders for oral solution or suspension are provided in a bottle for reconstitution with water before oral administration. These powder dosage forms offer the advantage of better physicochemical stability and longer shelf life over the corresponding liquid dosage forms.

The widespread usage of powders in the pharmaceutical industry and practice, therefore, requires a thorough understanding of their proper-ties and behavior to ensure their appropriate and efficient utilization. Powders—both excipients and active pharmaceutical ingredients (APIs)— can be amorphous or crystalline and possess different density, size, surface area, and flow properties. Mixtures of powders need to be uniform in the distribution of different powder components.

A key quality attribute of powders is the size and size distribution of their constituent particles. Often, efficient pharmaceutical processing or dosage form bioavailability requires increase or reduction of the particle size distribution (PSD) of the powder particles. PSD can be increased by powder agglomeration into larger, relatively stable aggregates in which the original particles maintain structural integrity and can still be identified. These aggregates are called granules. The process of preparing granules is commonly called granulation. Granulation of powders is frequently car-ried out during pharmaceutical manufacturing to improve the bulk prop-erties of the starting materials. Granulation can be carried out with or without the use of water—and is accordingly called dry or wet granu-lation. Reduction in the PSD of powders can be achieved by milling or comminution.

This chapter will introduce basic concepts of powder properties, their importance to pharmaceutical processing and dosage forms, and common techniques for modification of powder properties.