Plasma levels of oestrone, oestradiol and gonadotrophins in postmenopausal women after oral and vaginal administration of conjugated equine oestrogens (Premarin).

Peripheral plasma from five postmenopausal women was analyzed for oestrone and oestradiol during 48 hours after administration of 1.25 mg Premarin (conjugated equine oestrogen) orally and vaginally. Oestrone and oestradiol were separated on columns of Sephadex LH 20 before radioimmunoassay. Administration of 1.25 mg of Premarin produced a marked increase in plasma oestrone levels and 24 hours after treatment the oestrone levels were still above follicular phase levels. The plasma pattern of oestradiol was similar but the elevation was less pronounced. The biological activity of Premarin as indicated by depressed gonadotrophin levels was similar with the intravaginal and oral routes of administration.