Magnesium Stearate Fatty Acid Composition, Lubrication Performance and Tablet Properties

Magnesium stearate (MgSt) is a common tablet lubricant. As variations in MgSt properties are known to influence tablet attributes, the impact of MgSt fatty acid composition, particularly the significance of the stearate and palmitate contents, and its effects on tablet properties warrant further investigation. This study investigated the effect of MgSt with different stearate and palmitate contents but comparable physical properties (e.g. particle size, crystallinity, specific surface area and morphology) on lubrication performance and resulting tablet quality attributes, including mechanical strength, disintegratability and drug release. The influence of MgSt concentration and blending duration on the resulting tablet properties was also examined. Tablets produced using the lower stearate content MgSt had slightly higher tensile strength. The effect of MgSt stearate content was more apparent in the disintegration time and drug release, whereby MgSt of lower stearate content resulted in tablets with longer disintegration time and slower drug release. The lower stearate content also resulted in a lower lubrication performance, leading to a lesser reduction in tablet ejection force. As expected, a longer blending time of the tablet formulation blend with MgSt yielded tablets with reduced tensile strength, shorter disintegration time and slower drug release. Tablets with higher MgSt concentration showed a greater reduction in tensile strength, longer disintegration time and faster drug release. The study findings reinforced observations by other researchers and provided a better understanding of the fatty acid composition effects of MgSt on lubrication performance and the resulting tablet properties.

Introduction

Magnesium stearate (MgSt) is essential in tableting to prevent tablet adherence to surfaces of the die and punches, reduce interface friction and improve granule flowability [1, 2]. Due to its popularity as the lubricant in tablet formulation, MgSt has been widely investigated for its properties and potential impact on formulations. Variations in the MgSt properties have been reported to affect its lubrication performance and the properties of tablets produced [3,4,5,6,7]. Additionally, lubricant blending conditions [8,9,10,11] and tablet formulation components [12,13,14] were reported to influence the tableting process and hence, the resulting tablet properties. Therefore, care should be taken to maintain the MgSt properties and tableting process parameters for each batch of tablets manufactured to minimize inconsistencies in the tablet quality.

MgSt, as a tablet lubricant, primarily consists of magnesium stearate and magnesium palmitate in various proportions and other fatty acids in smaller proportions [15]. It is challenging to produce MgSt of varied stearate and palmitate contents while maintaining similar physical properties [16, 17]. A study attempted to synthesize pure magnesium stearate and pure magnesium palmitate and compare the thermal properties and morphology of the hydrates. The study reported that the pure magnesium stearate and pure magnesium palmitate had comparable thermal properties, except for the trihydrates. The study also observed that pure magnesium stearate generally had smaller particle sizes with irregularly shaped layered particles compared to pure magnesium palmitate, which had larger particle sizes with plate-like particles [18]. Wada and Matsubara reported MgSt of varied particle sizes and morphologies for stearate contents ranging from 57 to 77% and palmitate contents ranging from 23 to 41% [19]. The study also reported MgSt of comparable morphology with different particle sizes and stearate/palmitate contents. The fatty acid source, whether from animal or plant sources, has been reported to affect MgSt lubrication performance [20]. However, other studies have shown little to no difference in MgSt’s performance between the plant-based and animal-based MgSt [6, 21]. The effect of fatty acid composition on MgSt’s performance has been investigated by synthesizing MgSt of different stearate and palmitate contents. However, the fabricated MgSt showed different specific surface areas and crystal structures, potentially confounding the results [16, 22]. Clearly, the influence of the fatty acid composition of MgSt on its lubrication performance and resulting tablet properties has not been conclusively established.

Although much work has been performed on characterizing MgSt and MgSt’s effect on powder flow or the tableting process, the effect of the fatty acid composition is difficult to discern from the other properties [23,24,25]. The fatty acid composition needs to be deconvoluted from the other properties to further provide an understanding of its effect on lubrication performance and the resulting tablet properties. Using MgSt designed to contain different fatty acid compositions, this study aimed to elicit the effect of the primary fatty acids, stearate and palmitate. Herein, two MgSt grades of different stearate and palmitate contents but with comparable physical properties (such as particle size, crystallinity, specific surface area and morphology) were evaluated through their effect on the mechanical strength, ejection force, disintegration and dissolution properties of the tablets produced. The influence of MgSt concentration and blending duration on the resulting tablet properties was also investigated.

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Materials

Two MgSt grades of different fatty acid compositions – MGS-L (43.5% stearate, 54.9% palmitate, other carbon chains: insignificant, specific surface area: 3.4 m²/g) and MGS-H (70.4% stearate, 28.8% palmitate, other carbon chains: insignificant, specific surface area: 2.9 m²/g) were supplied by Faci Asia Pacific Pte. Ltd., Singapore. Other tablet components included microcrystalline cellulose (MCC; PH101, Asahi Kasei, Japan) as the filler, chlorpheniramine maleate (Vetpharm Laboratories Pte. Ltd., Singapore) as the model drug, and sodium starch glycolate (Primojel, DFE Pharma, Germany) as the disintegrant.

Veronica, N., Heng, P.W.S. & Liew, C.V. Magnesium Stearate Fatty Acid Composition, Lubrication Performance and Tablet Properties. AAPS PharmSciTech 25, 262 (2024). https://doi.org/10.1208/s12249-024-02980-x

Read also our introduction article on Magnesium Stearate here: