RELEASE CONTROL OF 9-BETA-D-ARABINOFURANOSYLADENINE FROM THERMORESPONSIVE GELS

Hydydrophilic 2-hydroxyethyl methacrylate (HEMA) and hydrophobic styre ne (St) were introduced into a thermo-responsive gel of acryloyl-L-pro line methyl ester (A-ProOMe) by means of radiation-induced copolymeriz ation in the presence of a slight amount of crosslinker. The copolymer gels showed a reversible volume phase transition around 14 degrees C and, as a result, it was found that the introduction of HEMA and St le ads to the formation of a 'matrix pumping' gel which is characterized by a rapid shrinkage of the whole matrix without the disappearance of pores in the initial stage of deswelling. Such a thermo-responsive fun ction appeared in limited composition ranges; 0-90 mol% HEMA and 0-50 mol% St. 9-beta-D-Arabinofuranosyladenine (Ara-A) was incorporated int o the A-ProOMe-containing gel to evaluate the release behavior of Ara- A when cycled between 10 and 37 degrees C. The drug resulted in a puls atile release consisting of a slight amount of drug release at 10 degr ees C and a good deal of drug release at 37 degrees C, in closely rela tion to a matrix pumping mechanism.