Impact of magnesium stearate physical and chemical variabilities on pharmaceutical powder flow and tablet physical properties

PurposeThis study aimed to elucidate the effects magnesium stearate (MgSt) with different physical properties have on powder flow and tablet physical properties. The effects of variation in MgSt chemical properties were also investigated with a focus on the palmitate to stearate (C16/C18) ratio.MethodsLactose blended with 0.25, 0.5 and 1%, w/w of different MgSt grades were evaluated for flow properties. Tablets produced from the mixtures were assessed for tensile strength and ejection force.ResultsPearson correlation analysis of high C16/C18 ratio (1.09-1.29) MgSt suggested that increasing C16/C18 ratio could improve flowability and reduce tablet mechanical strength. For low C16/C18 ratio (0.41-0.53) MgSt, increasing C16/C18 ratio only resulted in better flowability. Multivariate analysis showed that the MgSt properties influenced the flowability and tablet physical properties of formulations containing 1%, w/w MgSt. The C16/C18 ratio affected flowability. However, its effect was confounded by MgSt particle size, morphology, crystallinity, and moisture content. Contrastingly, tablet tensile strength was mainly influenced by MgSt particle size, crystallinity, and moisture content, while tablet ejection force was minimally affected by the MgSt properties.ConclusionWhile the C16/C18 ratio could affect the powder flow properties, the effect was confounded by other MgSt properties. The C16/C18 ratio also had minimal effect on tablet physical properties. The results further showed that although MgSt with smaller particle size, higher crystallinity and moisture content provided better flowability, the resultant tablets had lower tensile strength. These findings highlighted the importance of MgSt properties for formulations of good flowability and tablet physical properties.