Sustained suppression of pituitary-gonadal axis with an injectable, in situ forming implant of leuprolide acetate

The objective of these studies was to develop a leuprolide acetate depot based on an in situ forming drug delivery system (Atrigel(R)) to suppress the pituitary-gonadal axis and in turn the serum testosterone to chemical castration levels for a period of at least 3 months. Formulations with biodegradable lactide/glycolide copolymers that varied in molecular weight, lactide/glycolide ratio, and hydrophilicity were evaluated in rats for their efficacy by measuring serum testosterone levels. The effect of polymer irradiation was also investigated. Molecular weight of the polymers was characterized by gel-permeation chromatography, and retrieved implants at the termination of animal studies were assayed for residual drug content by high-performance liquid chromatography. These initial rat studies showed that a formulation containing a 75/25 lactide/glycolide copolymer dissolved in N-methyl-2-pyrrolidone with 3% w/w leuprolide acetate suppressed serum testosterone for a period of 3 months or longer. This formulation with its advantages of biodegradability, biocompatibility, ease of injection, and no need for removal after use should be beneficial in treating patients with hormonal-dependent prostate and mammary cancers, endometriosis, and precocious puberty. In addition, this formulation with its simple manufacturing process is expected to provide an economic benefit to the user compared with products currently available on the market.