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The "natural estrogens" containing pills
By Nathalie Chabbert-Buffet (France)
The development of oral contraception has been one of the great medical and social revolutions of the last century. Oral contraception is one of the most used techniques in many countries. As defined by the WHO, contraception must be efficient, reversible, affordable and well tolerated. In this perspective, the potential impact of the use of estrogens and progestins for contraception has been a subject of controversy for the last 10 to 15 years, especially concerning (arterial and venous) vascular risk as well as carcinologic risk.
Different generations of oral contraceptives (OCs) have been developed mainly to reduce the metabolic and vascular risk . The most recent, third generation oral contraceptives (OC), are an association of low dose ethinyl estradiol and potent testosterone related progestins, developed to improve general and vascular tolerance. They are highly efficient and well tolerated by most users. Their extensive use has provided different key information: OCs (and non oral ethinyl estradiol containing contraceptives) can be used in women under the age of 35 with well controlled metabolic risk factors and high familial risk of breast cancer. On the other hand ethinyl estradiol containing contraceptives are not indicated in women with a high risk of deep venous thrombosis, or non controlled metabolic and vascular risk factors (including age over 35 and cigarette smoking), or with a history of breast cancer. Progestin only contraception is not well tolerated due to bleeding.
The current hormonal contraception concepts contain "non testosterone-derived" progestins and "non ethinylated" estradiol.
Three type of such contraceptives are currently under development at different stages. The association of estradiol valerate and Dienogest has been launched in September 2009 in Europe. The association of estradiol and nomegestrol acetate is currently in phase 3 studies. The product has been submitted at the EMEA and it should be launched in 2010. Finally the association of estetrol (a placental estrogen) with different progestins is evaluated in phase 1 studies.
In this contraceptive concept the progestin is the antigonadotropic actor. This includes the need for relativement high doses of the progestin. The estrogen is added in order to avoid side effects of antigonadotropic progestins such as bleeding, vaginal dryness, and bone mineral density reduction.
The use of estradiol instead of ethinyl estradiol allows a dramatic reduction of the estrogenic activity. This reduction is related to the lower affinity for the estrogens receptor, a reduced number of enterohepatic cycles and a faster metabolization and excretion of inactive metabolites. It will thus reduce the impact on the different hepatic protein currently used as markers of metabolic and vascular risk. However data from the ESTHER study, conducted in post menopausal women, have shown that the risk of DVT still exists when estradiol is administered orally.
The use of nomegestrol acetate (NOMAC) as a progestin will allow a high progestogenic activity as well as a reduction in the impact of progestins on risk markers. NOMAC is a 19 nor progesterone derivative (or nor pregnane) which has a high bioactivity, related to its structure. The association of the suppression of the radical at carbone 19 (summarized as "nor" for no radical in the norpregnane name), of a double bound between carbon 6 and 7, as well as a modification of the substitution at carbon 17 leads to a high affinity for the progesterone receptor, the absence of affinity for SHBG (a high affinity steroid carrier protein) and a low affinity for both the androgen and the glucocorticoid receptors .
Clinical studies conducted on small numbers of women using NOMAC alone have shown that this molecule is able to block the LH surge as well as the FSH intercycle rise for doses of .5 mg/d or more, allowing anovulation in all women.The metabolic tolerance was good in normal women using NOMAC alone, as well as in women with dyslipidemia. Markers of thrombosis were not modified.
Phase II studies evaluating the effect of the association of NOMAC and estradiol 1.5 mg/d (NOMAC E2) have confirmed that the association also induced anovulation provided that the dose of NOMAC was 2.5 mg/d or higher. Interestingly the association showed some synergy in down regulating FSH and LH as compared to NOMAC alone (presented at the European Society of Gynecology congress 2009 in Rome). Furthermore the scheme of administration of NOMAC E2 24days /28 showed to be more efficient than the same association administered 21 days/28 (presented at the FIGO congress 2009 South Africa).
Unpublished phase III studies compared the association of NOMAC (2.5 mg/d)E2 (1.5 mg/d) 24 days /28 with the association ethinyl estradiol (30 µg/d) and drospirenone. The rates of pregnancy were lower, no matter the calculation technique, in the NOMAC E2 group. Bleeding patterns were comparable. The increase in SHBG was 33% in average.
These results provide evidence that the association of NOMAC (2.5 mg/d) with estradiol (1.5 mg/d) administered 24 d/28 is efficient for contraception and well tolerated.
This association will be indicated for women without a contra indication to oral contraceptives. It is not targeting high risk women.
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