[Water uptake of tablets, their disintegration and dissolution are in close relation]

Authors investigated the factors influencing this connection on phenylbutazone tablets. Tablets were prepared by wet granulation using three binders (gelatine, hydroxypropyl-cellulose, hydroxyethylcellulose) in different concentrations. Three disintegrants were compared (polyvinylpolypyrrolidon, formalin-casein and cyclodextrin polymer) on the basis of their disintegrating and dissolution-enhancing properties. It was found, that the binder having surface activity improves the wetting of phenylbutazone tablets. Increasing the concentration of gelatine solution, tablets became harder, disintegrated very slowly and the active agent hardly dissolved. Among disintegrants the polyvinyl polypyrrolidon was found to be the best. This material increases the hardness and the drug release as well. The use of cyclodextrin polymer is limited because of the slow water uptake of its tablets. The water uptake of nondisintegrating tablets was described with the Washburn equation. Water penetrates into disintegrating tablets according to the Weibull distribution. The penetration rate can be characterized with the "characteristic water penetration time (t63.2%), obtained from the Weibull equation. The difference between nondisintegrating and disintegrating tablets can be observed in the dissolution kinetic, too. The drug dissolves from the nondisintegrating tablets according to Noyes-Whitney equation (Eq. 1.), from disintegrating tablets according to the modified Noyes-Whitney equation (Eq. 2.) or Weibull equation (Eq. 3.). The dissolution rate constant (K) obtained from the modified Noyes-Whitney equation is proportional with water uptake and in inverse.