the present invention relates to a composition of matter for the time - dependent liberation of therapeutic agents . this composition of matter comprises a polymeric slab and a homogeneously dispersed enzyme which degrades the polymeric slab in the presence of moisture . the therapeutic agent is physically entrapped in the polymeric slab by inclusion during polymerization to form the polymeric slab or by mixture of the therapeutic agent with a liquid form of the polymeric slab and conversion of the liquid to a solid form . the therapeutic agent is not chemically bound to the polymer , and thus release of the agent is immediately effected upon the specific moisture - activated enzymatic degradation of the polymer slab . moisture for enzymatic activation is provided by the biological surface on which the slab is emplaced , such as the dermal surface . the composition comprises a polymer such as poly and an enzyme such as proteinase k together with chlorpheniramine maleate as the therapeutic agent .