A systematic investigation of external lubrication of mini-tablets on a rotary tablet press with focus on the tensile strength.

External lubrication is an alternative to internal lubrication and its related detrimental effects on properties of tablets like tensile strength (TS). However, to date there are hardly any systematic investigations on external lubrication of mini-tablets on rotary tablet presses. Aim of this study was the systematic investigation of the impact of parameters tableting pressure, tableting speed, dosing rate and air pressure on the TS of mini-tablets. Both studies, the Central Composite Design (CCD) with SMCC 90 and the subsequently executed D-optimal design with SMCC 50, exhibited that tableting pressure had the highest positive effect on TS. Tableting speed and dosing rate in the CCD presumably did not seem to influence the TS, air pressure represented a positive coefficient. An additional temporal factor seemed to impact the results, deduced from the negative effect of the experimental order on TS in the CCD and from the negative correlation along the execution order in the residual plots. Additional long runs support findings of a non-linear decrease of TS over time. An interplay between dosing rate level and performance of the dust extraction collector is assumed, making more magnesium stearate available in the tablet press and potentially causing gradual contamination of the powder over time.

Impact of alternative lubricants on process and tablet quality for direct compression.

Internal lubrication with magnesium stearate (MgSt) is associated with a reduced tensile strength and prolonged disintegration and dissolution times. In the current study, alternative lubricants to MgSt were compared with regard to lubrication efficacy and their impact on tablet properties. The lubricants were combined in different concentrations (0.5-5% w/w) with three fillers (lactose, mannitol and microcrystalline cellulose (MCC)). The high lubrication efficiency of MgSt was associated with the highest reduction of tensile strength. The micronized stearic acid (SA) grades proved good alternatives as they showed a good lubrication efficiency in combination with a limited negative effect on tensile strength. The hydrophobic lubricants (e.g., MgSt and SA) did not prolong disintegration. In contrast, delayed disintegration was observed for sucrose monopalmitate combined with all three fillers and for several other hydrophilic lubricants (sodium lauryl sulfate, poloxamers 188 and P407) combined with MCC. These unexpected findings were explained by the competition-for-water hypothesis. The potential of alternative lubricants to MgSt was demonstrated in this study. Nevertheless, the impact of lubricant addition on process and tablet quality depended on lubricant (type and concentration) and formulation (lubrication need, deformation mechanism and disintegration behavior) properties. Therefore, lubricant selection should be carefully considered in formulation development.

Effect of feed frame on lubricant sensitivity during upscaling from a compaction simulator to a rotary tablet press.

Internal lubrication can be associated with reduced tabletability. Deformation mechanism, lubricant type, lubricant blending time and paddle speed (PS) of the forced feeder are known to be influenceable factors. This study investigated the effect of lubricant blending time and PS of forced feeders on the tensile strength of lubricated microcrystalline cellulose (MCC) and lactose tablets. Magnesium stearate (MgSt), sodium stearyl fumarate (SSF) and stearic acid (SA) were used as lubricants. Tablets were produced on a compaction simulator and a rotary tablet press to investigate lubricant sensitivity during upscaling. Lubricant sensitivity was found higher for MCC compared to lactose which was attributed to the higher plasticity of MCC. The reduction in tensile strength upon lubricant addition followed the order: MgSt > SSF > SA; which could be linked to particle size, specific surface area and particle shape of the lubricants. Although differences in tensile strength were observed between the lubricant types, comparable ejection forces were obtained. The impact of PS on tensile strength was higher compared to lubricant blending time for both tableting machines. A good correlation of tensile strength and lubricant sensitivity between the compaction simulator and rotary tablet press was observed based on the calculation of paddle passes (NPP).