N-substituted cyclic lactam esters are made from biologically active organic acids and N-haloalkyl substituted cyclic lactam, preferably N-chloromethyl pyrrolidone. Such esters provide slow release of the organic acids in situ through slow hydrolysis of the ester to release the organic acid and the N-alkyl substituted cyclic lactam. The esters are useable for delivering a large variety of biologically active organic acids in slow release fashion to target organisms and promote effective long term therapeutic treatment. In particular, an ester made from acetyl salicyclic acid and chloromethyl pyrrolidone provides a vehicle for dermal penetration and slow release of aspirin for long term treatment.