Circulating levels of norethindrone in women with a single silastic implant

Abstract

In a group of women, norethindrone levels in serum have been measured up to 32 weeks after insertion of subdermal silastic implants containing norethindrone acetate. The initial levels were independent of body weight and the levels decreased with the duration of use. Although the bleeding pattern bore no direct correlation with the circulating level, those women having an initial level of more than 1500 pg/ml had irregular bleeding throughout the period of study.