[Factors influencing the in vitro and in vivo liberation of drugs from hydrogels].

Interactions of drugs containing macro-molecular agents (cellulose derivatives, polyvinylpyrrolidone) as determined by equilibrium dialyses influence on the in-vitro liberation (hydrophilic membrane) from hydrogels of the same viscosity acc. to the binding intensity. Utilizing a lipophilic membrane, this can be proved, too, the liberation intensity, however, is substantially determined by the lipoidwater distribution behaviour of the drugs. In-vivo liberations revealed in this, that differentiations in the liberation from methylcellulose and polyvinylpyrrolidone gels occur solely in drugs having a more intense affinity. The penetration intensity of the hydrogel into skin is, however, not caused by the binding tendency but by the lipoidwater distribution behaviour of the drugs. Analysing the in-vitro liberation with the use of a lipophilic membrane or knowing the distribution coefficient, informations on the level of the probable drug penetration gel/skin can be given.