In vivo characteristics of low‐molecular‐weight copoly( L ‐lactic acid/ DL ‐hydroxyisocaproic acid) with parabolic‐type and S‐type degradation pattersn

An amorphous copolyester of L‐lactic acid (LA) and DL‐hydroxyisocaproic acid (HICA) with a number‐average molecular weight (Mn) of 1600–4800 was synthesized by direct copolycondensation in the absence of catalysts, in order to develop a biodegradable carrier for drug delivery systems. The in vivo degradation pattern was changed into an S‐type from a parabolic‐type with an increase in molecular weight of copolyester. A luteinizing hormone‐releasing hormone agonist, des‐Gly10‐[D‐Leu6]‐LH‐RH ethylamide, was incorporated into a fine cylindrical copolyester formulation by the so‐called melt‐pressing technique. When the S‐type degradable and releasable copoly(LH/HICA) (70/30 mol‐%) formulations with Mn = 2200 were implanted subcutaneously in the back of rats, the most reasonable serum drug level was observed during the first 15 weeks period, keeping constant at approximately 3,5 ng/ml.