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

Plasma concentrations of ethynyl oestradiol and norethindrone in women were measured by radioimmunoassays after oral administration of 50 microng and 1000 microng respectively. The maximum values were obtained 1 h after administration. The calculated half-life was 6 1/2 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.