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• Electrostatic Charge: Static electricity can impede proper blending, which may be
mitigated by increasing humidity or using neutralizing agents .

• Adhering/Repelling Properties: Powders may adhere to or repel one another; inert
materials can be used to enhance blending .

Powder Processing: Size Reduction and Mixing

Size Reduction Techniques

Size reduction, or comminution, is performed to facilitate drug extraction, increase dissolution
rates, and enhance drug absorption by increasing the specific surface area of the substance .

• Small-Scale Methods (Pharmacy): Trituration is the reduction of particle size, typically
done using a mortar and pestle (a porcelain mortar achieves a finer grind) . Levigation
involves reducing particle size and grittiness in small-scale preparation of ointments
and suspensions, using a levigating agent (like mineral oil or glycerin) to create a
uniform paste .

• Large-Scale Techniques (Factories): Various mills and pulverizers are utilized .

Powder Mixture Types and Mixing Techniques

1. Types of Mixtures:

• Free-Flowing Mixtures (Random Mixing): These powders, which have similar particle
size, density, and shape, move independently and can easily segregate due to high
flowability . Segregation must be minimized by limiting shaking or bouncing .

• Cohesive Mixtures: These powders tend to clump together due to factors like moisture,
electrostatic charges, or Van der Waals forces, making them difficult to blend . They
require high mixing energy and shear to achieve uniformity .

• Ordered Mixing: This technique involves mixing larger, free-flowing particles with
smaller, cohesive particles that adhere to the larger surfaces . This yields a more
consistent blend and is used for powders with different sizes and densities .

2. Techniques for Blending Powders (Small-Scale):

• Trituration: Mixing powders in a mortar and pestle, often using geometric dilution to
ensure the even distribution of potent drugs . The mortar is generally more reliable for
mixing potent drugs than a spatula .

• Spatulation: Blending small amounts of powders using a spatula on a pill tile or
paper. It is not suitable for larger quantities due to the risk of segregation .

• Sifting: Passing powders through a sieve for a light, fluffy texture. This method is not
acceptable for incorporating potent drugs .

• Tumbling: Mixing powders in a rotating chamber for thorough blending, though it can
be time-consuming .

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