Using Laser Diffraction for Semisolid Formulations

Because they provide a solution to issues of bioavailability often seen in new drug candidates, semisolid drug formulations are becoming more and more common. These days, they make up a significant proportion of pharmaceutical dosage. When it comes to semisolid drug production, particle size is an undeniably crucial parameter. For this reason, finding an appropriate particle size analyser is of the utmost importance.

In this article, we’ll look at laser diffraction, a widely used method of particle size analysis that can be used for semisolid formulations at elevated temperature.

Why semisolids?

Something like 40 per cent of new chemical entities are challenging to modern drug delivery systems because of their poor aqueous solubility and low bioavailability. Semisolid formulations offer an answer to this problem. Additionally, patient compliance is improved, as semisolid products can be delivered painlessly and with minimal side effects.

Some examples of semisolid drugs include topical creams used for localised skin layer action (eg. Antiseptics and anaesthetics); as well as transdermal drugs that enter the body percutaneously. Semisolids have gained particular traction in transdermal delivery thanks to advances in delivery technology, such as slow release patches. When a transdermal patch is applied to the skin, the drug will enter the blood either through sweat ducts, hair follicles or the stratum corneum (the outer layer of the epidermis). However, the potential of the transdermal drugs to deliver the active ingredient is reliant on the semisolid’s rheological properties.

What makes a good semisolid?

The efficacy and safety of semisolid compounds are largely down to particle size and size distribution. These can have profound effects on bioavailability, dose uniformity and more. The relationship between product performance and particle size can be examined with data generated from the laser diffraction method of particle size analysis, which rests on the idea that particles that move through a laser beam will scatter light at an angle proportional to their size.

By applying stringent techniques in designing its particle size, the local efficacy of a drug’s entry can be maximised, and adverse reactions can be prevented. However, if settling or sedimentation occurs, efficacy will often be compromised due to irregular delivery.

Some of the methods of particle size analysis that have been used over the years include X-ray tomography, confocal imaging and scanning electron microscopy. However, these can usually only be applied while the product is being developed, and usually only with a small amount of material, which can cause problems when trying to characterise larger samples.

Laser diffraction: Why it’s the way forward

Laser diffraction, on the other hand, allows for very rapid measurement, accurate analysis, a broader measurement range, and the capability of looking at many sample types. One of its best properties is its sensitivity to changes in coarse particle fraction which makes it great for studying the instability that results from sedimentation or agglomeration. Additionally, the latest laser diffraction systems are completely automated and user-friendly.

One of the problems with using laser diffraction for semi-solids, however, is that samples are not liquid at room temperature. To deal with this, the laser diffraction system can be equipped with a dispersion cell and water bath, elevating the temperature to make more detailed particle size measurements.

Find the right particle size analyser

It’s important that you not only use the best method for analysing semisolid formulations at elevated temperature, but also use the best instrument. ATS Scientific is a trusted brand that offers a range of quality particle size analysers. Contact us today for more information.