An evaluation of the pharmacokinetics and pharmacodynamics of the histrelin implant for the palliative treatment of prostate cancer.

Seventeen patients with advanced prostate cancer were studied to evaluate the pharmacokinetics and pharmacodynamics of a hydrogel implant designed to deliver histrelin at a constant rate (50 microg/d) for 1 year. Serum histrelin levels were collected during the 52-week implantation period and after a second implant. Testosterone suppression was the primary pharmacodynamic endpoint, with treatment success defined as serum testosterone less than 50 ng/dL. The histrelin subdermal implant delivered constant histrelin levels, with mean serum histrelin of approximately 0.265 ng/mL over 52 weeks. At the end of 52 weeks, mean histrelin concentrations were 0.128 +/- 0.0652 ng/mL. Patients achieved chemical castration (testosterone less than 50 ng/mL) by week 4. In patients who had the first implant removed and received a new implant at the end of the first 52 weeks, testosterone suppression was not interrupted. The hydrogel implant provided consistent delivery of histrelin over 1 year and effectively suppressed testosterone in men with prostate cancer.