Manufacturing processes

Manufacturing processes

Laboratory scale

Preparation of semisolid dosage forms on a laboratory or compounding pharmacy scale can be accomplished using one or more of the following techniques and principles:

·           Geometric mixing using a spatula on a plate. This allows uniform incorporation of a small quantity of an ingredient into a large quan-tity of the other ingredient(s). Geometric mixing involves mixing a small quantity ingredient with the same volumetric or weight quantity of the larger quantity ingredient, followed by repeating this procedure with the small component mix until all the large quantity ingredient has been incorporated.

·           Powder communition or particle size reduction by grinding in a pestle and mortar.

·           Levigation by grinding the powder in a small quantity of suitable levi-gation aid in a pestle and mortar, followed by geometric mixing with the base using a spatula on a plate.

·           Fusion by melting the components together on a water bath.

·           Using pestle and mortar to prepare an emulsion concentrate using lower quantity of the external or continuous phase, followed by dilu-tion of the emulsion concentrate to volume.

Industrial scale

Manufacture of semisolid dosage forms on a large scale presents challenges with respect to the inherent viscosity of the formulation, non-Newtonian flow characteristics, possibility of air entrapment, heat distribution within a vessel, variation in the volume of liquid components with changes in oper-ating or ambient temperature, and the energy requirement for efficient mix-ing of viscous fluids.

On a pilot plant to a production scale, semisolid formulations are manu-factured using one or more of the following equipment and techniques:

1.        Electrically operated propeller mixer in a suitable mixing vessel.

2.        Temperature control using jacketed mixing vessel, with the jacket having a supply of hot or cold water or steam. The mixing vessel also often has a mixer that sweeps close to the wall to prevent overheating and allow mixing of semisolid mass, which otherwise has low convec-tive mixing rate.

3.        Homogenization using a homogenizer mixer or a colloid mill.

4.        Use of proportioning pump to allow simultaneous blending of phases.

5.        Transfer of the semisolid material from one unit operation to another, or to the packaging line, in a container, gravity-facilitated, if feasible, or pumping through a tube.

The choice of technique depends on rheological properties of the formula-tion in addition to plant design and feasibility of equipment.