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Abstract
Trimegestone is a novel norpregnane progestin, which has a potent progesterone receptor and very low androgen receptor affinities but no detectable affinity to oestrogen receptor. Trimegestone has been developed for use in conjunction with oestrogen for postmenopausal hormone replacement therapy (HRT). The dose of trimegestone required for endometrial safety was optimised in a dose ranging study. Oral trimegestone was administered at 0.05, 0.1, 0.25 and 0.5 mg/day, days 15 - 28 along with continuous oral micronised oestradiol at 2 mg daily. The majority of women in the four dose groups experienced relief of climacteric symptoms by the end of the third treatment cycle. The incidence of pre-menstrual tension-like symptoms was low and did not differ between the four dose groups. After 6 months of treatment, the bleeding pattern showed a clear dose-dependent modulation such that the higher the dose of trimegestone administered the more predictable was the day of onset of bleeding and the shorter and lighter the bleeding episodes became. This was further confirmed in another study comparing trimegestone in 0.5 and 0.25 mg doses to norethisterone acetate, where women on the 0.5 mg dose experienced more favourable bleeding pattern compared with the lower dose of 0.25 mg or to norethisterone acetate. In the dose ranging study, 96% of endometrial specimens obtained at the end of the study had secretory changes. The lipoprotein profile measured at baseline, 3 and 6 months during the dose ranging study confirmed the fact that trimegestone, irrespective of the dose, did not negate the beneficial effects of oestrogen on lipids. Conclusion: trimegestone is an effective and well-tolerated new progestin, which does not negate the beneficial effects of oestrogen on lipids.