Plasma concentrations of ethynyl oestradiol and norethindrone after oral administration to women

Summary.Plasma concentrations of ethynyl oestradiol and norethindrone in women were measured by radioimmunoassays after oral administration of 50 μg and 1000 μg respectively. The maximum values were obtained 1 h after administration. The calculated half-life was 6½ h for ethynyl oestradiol and 7 h for norethindrone. At most 2–3% of the administered dose was present in the plasma at 1 h and had decreased to about 0·5% by 24 h.