title: Pharmacokinetics of norethindrone acetate in women after the insertion of a single subdermal implant releasing norethindrone acetate.
abstract: The metabolic clearance rate (MCR) of norethindrone acetate (NETA) and norethindrone (NET) levels in plasma were studied after an iv injection of [3H]NETA in three women before and at 1 week, 1, 2 and 6 months following the insertion of a single silastic subdermal implant releasing microquantities of NETA. No significant change in the MCR of NETA was observed at 1 week (459 +/- 72 1/day), 1 month (489 +/- 113 1/day) and 2 months (522 +/- 144 1/day) compared with that of control (525 +/- 108 1/day). However, MCR of NETA showed significant increase in women exposed to continuous presence of NETA for a period of 6 months (608 +/- 121 1/day; P less than 0.025). NETA was rapidly and extensively metabolized into NET. At 1 week, 1, 2 and 6 months of study, NET was observed to be present in higher amounts compared with NETA. The production rate (PR) of progesterone decreased significantly at 2 and 6 months of NETA implant insertion compared with the PR before the insertion of implant.
mesh_terms: D000328:Adult; D004343:Drug Implants; D005260:Female; D006207:Half-Life; D006801:Humans; D007700:Kinetics; D008657:Metabolic Clearance Rate; D009640:Norethindrone / Q000031:analogs & derivatives* / Q000097:blood*; D000077563:Norethindrone Acetate; D011374:Progesterone / Q000097:blood
chemical_list: D004343:Drug Implants; D011374:Progesterone; D000077563:Norethindrone Acetate; D009640:Norethindrone