Liquid Penetration Testing in Commercialized Tablets

Background: Liquid penetration tests are mostly performed in the research stage of formulation design of tablet, but the author reports the results of liquid penetration tests on commercially available tablets. Methods:The rate of liquid penetration was measured in two ways: by measuring the time required for a given amount (10μl) of liquid to be completely absorbed into the tablet (test 1), and by measuring the relationship between the amount of liquid absorbed by the tablet and the elapsed time (test 2). The liquids used in the penetration tests were ethyl acetoacetate and water. Results and Discussion: The variation in weight and thickness of Tablets A, B, C, and D used in (test 1) was small, with the coefficient of variation being approximately 1% or less. In contrast, the coefficient of variation in liquid absorption time was large, at 10-20%. A significant positive correlation was observed between the absorption time and the tablet weight/thickness ratio for each product, and it was confirmed that the liquid absorption time increases as the tablet weight/thickness ratio increases. The liquid absorption time of the Tablet A-old product was clearly shorter than that of new product. The shorter liquid absorption time of the older Tablet A products may suggest a change in the pore structure due to moisture absorption.In the ethyl acetoacetate penetration into Tablet A (test 2),square of permeated volume: V 2 vs. elapsed time: t plot and Log V vs. Log t plot showed a good linearity, and slopes of regression line of Log V vs. Log t plot was approximately 0.5.suggesting that the penetration of ethyl acetoacetate follows the Washburn equation. On the other hand, for the penetration of water into tablets A and B, the V2 vs. t plot did not show linearity, but the Log V vs. Log t plot showed good linearity, and the slope of the regression line was much greater than 0.5. This suggests that the permeation of water into tablets A and B caused a significant change in the pore structure due to swelling. Furthermore, the intercept of the regression line of the Log V vs. Log t plot of the water permeability of tablet B showed a significant negative correlation with the tablet weight. The intercept of the regression line, Log t = 0, is the permeation volume at t = 1 (seconds). This suggests that for tablets with an almost constant volume, the weight fluctuation of the filling particles has a significant effect on the tablet's bulk density, and therefore on its porosity and initial permeation rate. Conclusion: The method attempted by the author is simple and will be useful for analyzing the disintegration and internal structure of commercially available tablets.