Particle Size Analysis for the Pharmaceutical Industry

Particle size strongly relates to flowability, content uniformity, bioavailability, dissolution and absorption behavior, which are crucial parameters in the pharmaceutical industry. Hence, product effectiveness as well as production processes are influenced by particle size, making it important to characterize both active components and excipients. Here, we measure the particle size and distribution of three lactose powders destined as an excipient for different pharmaceutical applications.

Particle size is a crucial parameter in the pharmaceutical industry, because it influences surface area and porosity and, hence, has an impact on bioavailability, effectiveness and shelf life of a drug. Therefore, particle size is not only monitored in quality control, but also in the development of new active pharmaceutical ingredients (APIs). In fact, particle size distribution (PSD) is among the most important parameters to check when evaluating new drugs. E.g. particle size is critical for powder inhalers that are commonly used in the treatment of various lung diseases to deliver the corresponding API as a powder to the lungs. The drug is prepared as a powder and is inhaled without the need of anypropellant gas. The API can be applied in pure form or adhered to a carrier material, such as lactose (1).

Particle size also greatly affects tableting and granulation processes. On the one hand, small particles aid dissolution, but are also more sensitive to overcompression, leading to hard tablets which barelydisintegrate. Large particles on the other hand, lead to better flowability, compressibility and feeder clearance during the manufacturing process. Moreover, a more homogeneous distribution is achieved, if particles exhibit a narrow particle size distribution (2).

PSD influences not only the production process and the behavior of a drug, but also the administrative efforts. Namely, a narrow PSD facilitates the specification of new drugs in respect to the FDA process validation guidelines and the International Conference on Harmonization (ICH) guideline Q6A (3)(4).

In this application report we measured the PSD of different samples of lactose. Lactose (α - lactose) is a disaccharide consisting of galactose and glucose,showing great flowability and compressibility. It is used as an excipient for tableting, filler for capsules or carrier powder in inhalers in the pharmaceutical industry (5).

Laser diffraction is one of the most common techniques for particle size analysis, based on the observation that the angle of laser light diffracted by a particle corresponds to the size of the particle. This measurement technique is in accordance with the US and European pharmacopeia (USP 429, EP 2.9.31), which gives guidance concerning laser diffraction methods used for particle size measurements in the pharmaceutical industry.

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