Effect of Diluents on Active Pharmaceutical Ingredient Loss Until Patients Ingest Powder Formulation

In powder formulations, it is a problem that the required therapeutic dose is not obtained because of loss of the active pharmaceutical ingredient (API). In this study, we investigated three types of lactose diluents, which are widely used as pharmaceutical excipients, for dispensing prednisolone powder. Extra-fine crystalline lactose, commonly used as a diluent in compounding powder formulations, was used as a comparison. The effect of lactose on the API loss rate was examined by analyzing the amount of prednisolone in the powder formulation taken out of a single-dose package after dispensing. The results showed that Dilactose-F had the lowest API loss rate (22%), followed by powder lactose (37.8%), extra-fine crystalline lactose (45.9%), and crystal form lactose (48.6%), indicating that the use of Dilactose-F as a diluent significantly improved API loss when compounding the powder formulation. Because each mixture of commercial prednisolone powder and lactose was within acceptable uniformity and loss rate before packaging, we considered that API loss occurred when the powder was taken out of the single-dose package before patients ingested them. Then, the physical properties of these lactose types affecting the API loss rate were examined. Strong correlation was not found between flowability and the API loss rate, but particle size distribution and bulk density were strongly correlated with the API loss rate. Furthermore, Dilactose-F, which showed the lowest API loss rate, did not show an exothermic peak due to epimerization to anhydrous β -lactose in differential scanning calorimetry and showed a peak specific to β -lactose in powder X-ray diffractometer. These results suggested that in powder compounding where the API content is low, the physical properties of lactose, such as particle size distribution, bulk density, and crystalline form, are intricately related to API loss.