Formulation study of leuprorelin acetate to improve clinical performance

Leuprorelin acetate, a highly potent gonadotrophin-releasing hormone agonist, was originally launched in the USA as a daily injection for the treatment of metastatic prostatic cancer. A once-monthly injectable depot form was subsequently developed. Biodegradable copoly(DL-lactic/glycolic) acid was chosen as the release-controlling polymer, and microspheres containing leuprorelin acetate were prepared by the in-water drying method. Results of studies in rats showed that a copolymer with a molecular weight of 14,000 and a lactic/glycolic acid ratio of 75/25 had the most satisfactory release-controlling properties. Microspheres given once monthly reduced serum testosterone levels in male rats. Microspheres also reduced serum oestradiol levels and caused a marked regression in experimental endometriosis in female rats. In clinical studies of prostatic cancer, use of the depot formulation has effectively reduced the dose required to as low as one-eighth of that needed for administration by daily injection. A sophisticated manufacturing system has now been developed and products now available have many advantages.