Prekliinisten suspensioiden valmistus, fysikaalinen karakterisointi ja säilyvyys

Suspension is nowadays the most commonly used dosage form in preclinical animal studies. However, suspension can be physically unstable and changes in particle size or crystal form of an active pharmaceutical ingredient (API) can occur during storage. Conventionally suspensions are also prepared in a mortar, and hence the quality of suspensions is operator-dependent. One of the aims in this study was to prepare suspensions using a mortar and pestle and an Ultra-turrax homogenizer to find out how the preparation method affects the particle size of suspension. A solution containing methylcellulose and Tween 80 was used as a vehicle, and five active APIs with different physico-chemical properties as model drugs. Moreover, an aim of the study was to evaluate the stability of the suspensions stored at room temperature and in the refrigerator and freezer by physical (laser diffraction, optical microscopy, X-ray powder diffraction) and chemical (high-performance liquid chromatography) methods of analysis. The aim of the study was also to assess and compare the suitability of laser diffraction and optical microscopy for the determination of partice size during preclinical studies. The suspensions prepared using a mortar and pestle and Ultra-turrax had a similar particle size in almost all cases. The particle size of API that was difficult to grind decreased significantly, also when using Ultra-turrax although the capacity used was minimum. Both prepation methods had the best repeatability of particle size when the API was easy to grind. However, Ultra-turrax could provide better homogeneity of quality than a mortar and pestle if the settings were optimized. The effect of different operators was not studied in this study. The stability of suspensions in different storage conditions was dependent on the properties of API. The particle size of all frozen suspensions decreased after two days based on laser diffraction results. Although the reason was not found from literature or supplementary tests (particle size analysis of the vehicle and pH-measurements), freezing of suspensions should be treated with caution based on this study. The crystal structures of APIs remained stabile with the exception of typical disproportionation of the API salt. Suspensions were mainly chemically stabile in all conditions, but water-solubility of API seemed to decrease stability. The micellar solubilization of drugs was also observed. The best way to determine the particle size of preclinical suspensions proved to be the combination of laser diffraction and optical microscopy images. The microscopy images confirmed the validity of the size distributions measured by laser diffraction and provided information about e.g. particle aggregation. On the other hand, optical microscopy image analysis was not suitable method for particle sizing.