The Rate of Penetration of Liquid into Tablets. II. Influence of Second Ingredient and Mixing Ratio

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The influence of a second ingredient having a high contact angle on liquid penetration into tablets was tested and compared with the result obtained for powder. The contact angles of hydrophobic substances and mixed powders with excipients were measured by Kossen's method. The liquid penetration into powders and tablets of magnesium oxide and bromvalerylurea in various mixing ratios could be described by Washburn's equation. The penetration into mixed powders of magnesium silicate with bromvalerylurea, in spite of the large porosity of the powders, was delayed compared with that into the tablets. The penetration, however, was facilitated by the replacement of magnesium silicate with phenobarbital. The penetration into tablets of microcrystalline cellulose (M.C.C.) and magnesium stearate could not be described by Washburn's equation, as was the case for tablets prepared from M.C.C. A theoretical explanation for the experimental equation L=Kt, which had previously been introduced for the M.C.C. tablets, is discussed. The penetration into the tablets could be described by this equation when the amount of second ingredient in M.C.C. was small. When the amount of second ingredient was increased, however, the penetration into the tablets could not be described by Washburn's equation or by the equation L=Kt. The penetration into the mixed powders was fairly well described by Washburn's equation.