Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2020 Publisher: Marketing Authorisation Holder: Novo Nordisk Limited, 3 City Place, Beehive Ring Road, Gatwick, West Sussex, RH6 0PA
Pharmacotherapeutic group: Progestagens and oestrogens, sequential preparations
ATC code: G03FB05
Estradiol: The active ingredient, synthetic 17β-estradiol, is chemically and biologically identical to endogenous human estradiol. It substitutes for the loss of oestrogen production in postmenopausal women and alleviates menopausal symptoms.
Oestrogens prevent bone loss following menopause or ovariectomy.
Norethisterone acetate: Synthetic progestagen. As oestrogens promote the growth of the endometrium, unopposed oestrogens increase the risk of endometrial hyperplasia and cancer. The addition of a progestagen reduces the oestrogen-induced risk of endometrial hyperplasia in non-hysterectomised women.
Relief of postmenopausal symptoms is achieved during the first few weeks of treatment.
In a post-marketing study regular withdrawal bleeding with a mean duration of 3-4 days occurred in 91% of women who took Novofem over 6 months. Withdrawal bleeding usually started a few days after the last tablet of the progestagen phase.
Oestrogen deficiency at menopause is associated with an increased bone turnover and decline in bone mass. The effect of oestrogens on the bone mineral density is dose-dependent. Protection appears to be effective for as long as treatment is continued. After discontinuation of HRT, bone mass is lost at a rate similar to that in untreated women.
Evidence from the WHI trial and meta-analysis of trials show that current use of HRT, oestrogen alone or in combination with a progestagen – given to predominantly healthy women – reduces the risk of hip, vertebral, and other osteoporotic fractures. HRT may also prevent fractures in women with low bone density and/or established osteoporosis, but the evidence for that is limited.
Randomised, double-blind, placebo-controlled studies showed that 1 mg estradiol prevents the postmenopausal loss of bone minerals and increases the bone mineral density. The responses in the spine, femoral neck and trochanter were 2.8%, 1.6% and 2.5%, respectively, over 2 years with 1 mg 17ß-estradiol unopposed.
Following oral administration of 17β-estradiol in micronised form, rapid absorption from the gastrointestinal tract occurs. It undergoes extensive first-pass metabolism in the liver and other enteric organs, and a peak plasma concentration of approximately 27 pg/ml (range 13-40 pg/ml) occurs within 6 hours after intake of 1 mg. The area under the curve (AUC(0-tz))= 629 h x pg/ml. The half-life of 17β-estradiol is about 25 hours. It circulates bound to SHBG (37%) and to albumin (61%), while only approximately 1-2% is unbound. Metabolism of 17β-estradiol occurs mainly in the liver and the gut but also in target organs, and involves the formation of less active or inactive metabolites, including oestrone, catecholoestrogens and several oestrogen sulfates and glucuronides. Oestrogens are excreted with the bile, hydrolysed and reabsorbed (enterohepatic circulation), and mainly eliminated in urine in biologically inactive form.
After oral administration, norethisterone acetate is rapidly absorbed and transformed to norethisterone (NET). It undergoes first-pass metabolism in the liver and other enteric organs, and reaches a peak plasma concentration of approximately 9 ng/ml (range 6-11 ng/ml) within 1 hour after intake of 1 mg. The area under the curve (AUC(0-tz)) = 29 h x pg/ml. The terminal half-life of NET is about 10 hours. NET binds to SHBG (36%) and to albumin (61%). The most important metabolites are isomers of 5α-dihydro-NET and of tetrahydro-NET, which are excreted mainly in the urine as sulfate or glucuronide conjugates.
The pharmacokinetics of estradiol is not influenced by norethisterone acetate.
The pharmacokinetic properties in the elderly have not been studied.
Animal studies with estradiol and norethisterone acetate have shown oestrogenic and progestagenic effects as expected. Both compounds induced adverse effects in preclinical reproductive toxicity studies, in particular embryotoxic effects and anomalies in urogenital tract development. Concerning other preclinic effects, the toxicity profiles of estradiol and norethisterone acetate are well-known and reveal no particular human risks beyond those discussed in other sections of the Summary of Product Characteristics and which generally apply to hormone substitution therapy.
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