Plasma Estriol Levels after Intramuscular Injection of Estriol and Two of Its Esters<sup>1</sup>

Abstract

Twelve female volunteers from Berlin and 9 from Stockholm, all using a contraceptive pill (30 micrograms ethinyl estradiol and 150 micrograms levonorgestrel), received an intramuscular injection of estriol (E3; 1 mg in oil) on day 5 of withdrawal bleeding. Blood samples were collected at increasing time intervals during 4 weeks. Three months later, on day 5 of their withdrawal bleeding, 6 women were given intramuscularly (in oil) estriol 3,17-dipropionate (E3-prop) and 15 women estriol 3,17-dihexanoate (E3-hex). The doses were equivalent to 5 mg of estriol, i.e. 6.94 and 8.90 mg, respectively. Blood samples were collected during a period of 9 weeks. Estriol was analyzed by radioimmunoassay in all plasma samples. The average half-life of E3 ranged from 1.5 to 5.3 h after the administration of E3. It was 12.7 h and between 187 and 221 h after the administration of E3-prop and E3-hex, respectively. The average areas under the curve (in nmol.l-1.h) of E3 were between 82.5 and 161 after the administration of E3-prop or E3-hex, and between 27.1 and 37.9 when E3 had been given. As E3 was administered in a 5-fold lower dose than the esters, the areas under curve appeared to be comparable. Thus, the total exposure to E3 seemed to be almost independent of the type of E3 derivatization, while the time and intensity of exposure were very different.