Sustained pharmacological activities in rats following single and repeated administration of once-a-month injectable microspheres of leuprolide acetate.

Once-a-month injectable microspheres of leuprolide acetate prepared with copoly(DL-lactic/glycolic acid) using an in-water drying method were assessed for duration of the analogue release and pharmacological effects in rats after a single or repeated injection. The periodic challenge test revealed that a single injection of the microspheres caused a dramatic and persistent suppression of the ability of the pituitary-gonadal system to secrete gonadotropin and testosterone for over 5 weeks. The complete recovery of these functions was observed 10 weeks after the injection. The repeated injection of the microspheres at intervals of 2 or 4 weeks achieved persistent suppression of steroidogenesis after an initial transient flare-up and beneficially avoided the "acute-on-chronic response." This depot formulation is expected to assure patient compliance and produce stronger therapeutic effects than the daily solution.