Possibilities of mixing powder mixtures for capsules using three-dimensional mixer devices in pharmacy practice

Preparing oral powders for filling of hard capsules is one of the basic activities in pharmacies. One of the key operations that affects the resulting homogeneity of the substances in the mixture is the mixing process. Until recently, most pharmacies have used only a porcelain mortar and pestle for the mixing process, where the homogeneity of the resulting mixture is highly dependent on the experience and thoroughness of the preparing pharmacist or pharmacy assistant. In recent years, compact mixing devices that can be used in the pharmacy environment have become more widely employed. One of them is the FagronLab™ InvoMatic three-dimensional mixer. This paper evaluates the efficacy of the mixing process for a model substance using this device with three commonly available fillers. Mixing cycles were tested with different mixing speed and the same mixing time, which was set at 10 minutes. The results were compared to manual or ceramic-bead mixing. The material of the mixing vessel was also evaluated. Crystalline sodium chloride (NaCl) was chosen as the model substance, which was crushed into a fine powder before the mixing process. The individual NaCl contents in the capsules were determined using potentiometric argentometric titration with a 0.01 M silver nitrate (AgNO3) solution. With one exception, the device provided a sufficiently homogeneous mixture for the preparation of oral powders, when the RSD1 value was not greater than 5. Capsules met the content uniformity test according to Czech Pharmacopoeia 2023, article 2.9.40 Uniformity of dosage units. Acceptance value (AV) was less than 15.