Impact of process parameters on Mg–St content and tablet surface wettability in the external lubrication method for a rotary tablet press

• Tablet wettability by external lubrication was lower than by internal method.
• Tablet wettability can be controlled by the setting of external lubrication system.
• Critical process parameters for Mg–St content were statistically verified.
• Model equation to predict Mg–St content of external lubrication method was shown.

External lubrication is a new alternative used in compression processes of the pharmaceutical industry to minimize the negative effect of lubricant and to resolve sticking problems. This method can also prevent the deterioration of tablet properties; e.g., reduced tensile strength and a retarded rate of drug dissolution. The current study prepared tablets using the external lubrication method with varying potential critical process parameters and clarified the process of external lubrication via statistical analysis. In accordance with past results, tablets prepared using the external lubrication method had better tablet properties (higher hardness and more rapid disintegration) than those prepared using the internal lubrication method. Quantitative analyses of the magnesium stearate content and contact angle showed that the wettability of the tablet surface increased with the magnesium stearate content. Analysis of variance showed that all potential critical parameters are influential for the magnesium stearate content, but not for the disintegration of tablets. In addition, predictions of the magnesium stearate content and disintegration time of tablets made using a model equation correlated well with observed values. The external lubrication method can thus be applied by identifying the critical process parameters in the compression process during the development and manufacture of pharmaceutical products.

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