Subcutaneous Controlled Delivery of Estradiol by Compudose° Implants: in Vitro and in vivo Evaluations

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Abstract
The in vitro and in vivo releases of estradiol from the recently marketed Compudose°-200 and -400 implants were evaluated. These subdermal implants are designed for subcutaneous controlled administration of estradiol in steers for 200- or 400-day growth promotion. Analysis of the in vitro release profiles of estradiol from Compudose implants indicated that the release of estradiol is under a matrix diffusion-controlled process and follows a linear Q vs. t1/2 relationship. The release flux from both Compudose-200 and -400 implants was found to be dependent upon the volume fraction of polyethylene glycol 400, which acts as the solubilizer for estradiol, in the aqueous elution solution. Subcutaneous release of estradiol from Compudose implants was also conducted in laboratory rats for a duration of up to 114 days. Results indicated that the Q vs. t1/2 linearity is also followed. The subcutaneous rate of release was calculated to be 520 mcg/cm2/day1/2 for Compudose-200 and 360 mcg/cm2/day1/2 for Compudose-400.