Y. Yonezawa et al., DISSOLUTION OF SOLID DOSAGE FORM .7. EFFECT OF SHAPE ON THE DISSOLUTION OF NONDISINTEGRATING SINGLE-COMPONENT TABLET UNDER NON-SINK CONDITION, Chemical and Pharmaceutical Bulletin, 44(5), 1996, pp. 1043-1048
Effect of tablet shape on dissolution was examined as an example of th
e application of the z-law and Ln-z equations. The tablet shape can be
altered systematically by changing the diameter and weight of tablet,
since these equations were applicable for dissolutions with various o
ptional initial amounts within the amount required to saturate the sol
ution. It was confirmed that the z-law and Ln-z equations efficientl;y
heated the dissolution of tablet irrespective of the weight and size,
i.e., the diameter and thickness as well as crystalline particles. Bo
th dissolution equations gave almost the same dissolution rate constan
ts for a tablet of a fixed weight and size. The dissolution rate const
ant changed with the tablet weight and size, and it was suggested that
the latter factor probably had greater effect. The tablet size was th
en converted to the degree of isometricity or shape factor. Then, the
effect of shape on the dissolution rate constants of tablets (k(z)) wa
s estimated using the z-law equation. The k(z)-value of a long cylindr
ical tablet was large, and it decreased to reach a minimum value with
decrease in tablet thickness and increase in diameter. The k(z)-value
increased to reach almost a fixed value of shallow cylindrical tablets
as if it had been obtained by a rotating disk method. The difference
in the dissolution rate constants was examined using a specially devis
ed tablet of which the flat-faced surface or curved surface was coated
with wax. Dissolutions with these tablets suggested that the dissolut
ion rate constant of the long cylindrical tablet was the larger of the
two. Also, the way in which the flat-faced and curved surfaces contri
bute to the k(z)-value was examined as a function of the ratio of Bat-
faced surface area (2S(d)) to the whole surface area (S-o), i.e., 2S(d
)/S-o. The k(z)-value decreased almost straightly within the 2S(d)/S-o
-value reached to around 0.63, showing a close similar value where the
2S(d)/S-o-value was larger than around 0.73. Thus, it was suggested t
hat the tablet form should be taken into consideration when necessary.