I'm not sure if this helps but here's some info on letrozole and arimidex:
Letrozole:
Mechanism of Action
The growth of some cancers of the breast are stimulated or maintained by estrogens. Treatment of breast cancer thought to be hormonally responsive (i.e., estrogen and/or progesterone receptor positive or receptor unknown) has included a variety of efforts to decrease estrogen levels (ovariectomy, adrenalectomy, hypophysectomy) or inhibit estrogen effects (antiestrogens and progestational agents). These interventions lead to decreased tumor mass or delayed progression of tumor growth in some women.
In postmenopausal women, estrogens are mainly derived from the action of the aromatase enzyme, which converts adrenal androgens (primarily androstenedione and testosterone) to estrone and estradiol. The suppression of estrogen biosynthesis in peripheral tissues and in the cancer tissue itself can therefore be achieved by specifically inhibiting the aromatase enzyme.
Letrozole is a nonsteroidal competitive inhibitor of the aromatase enzyme system; it inhibits the conversion of androgens to estrogens. In adult nontumor- and tumorbearing female animals, letrozole is as effective as ovariectomy in reducing uterine weight, elevating serum LH, and causing the regression of estrogen-dependent tumors. In contrast to ovariectomy, treatment with letrozole does not lead to an increase in serum FSH. Letrozole selectively inhibits gonadal steroidogenesis but has no significant effect on adrenal mineralocorticoid or glucocorticoid synthesis.
Letrozole inhibits the aromatase enzyme by competitively binding to the heme of the cytochrome P450 subunit of the enzyme, resulting in a reduction of estrogen biosynthesis in all tissues. Treatment of women with letrozole significantly lowers serum estrone, estradiol and estrone sulfate and has not been shown to significantly affect adrenal corticosteroid synthesis, aldosterone synthesis, or synthesis of thyroid hormones.
Pharmacokinetics
Letrozole is rapidly and completely absorbed from the gastrointestinal tract and absorption is not affected by food. It is metabolized slowly to an inactive metabolite whose glucuronide conjugate is excreted renally, representing the major clearance pathway. About 90% of radiolabeled letrozole is recovered in urine. Letrozoles terminal elimination half-life is about 2 days and steady-state plasma concentration after daily 2.5mg dosing is reached in 2-6 weeks. Plasma concentrations at steady-state are 1.5 to 2 times higher than predicted from the concentrations measured after a single dose, indicating a slight nonlinearity in the pharmacokinetics of letrozole upon daily administration of 2.5mg. These steady-state levels are maintained over extended periods, however, and continuous accumulation of letrozole does not occur. Letrozole is weakly protein bound and has a large volume of distribution (approximately 1.9 L/kg).
Arimidex
Arimidex® (generic name is anastrozole) is a very new drug developed for the treatment of advanced breast cancer in women. It is manufactured by Zenica Pharmaceuticals and was approved for use in the United States at the end of December 1995. Specifically, Arimidex® is the first in a new class of third-generation selective oral aromatase inhibitors5°. It acts by blocking the enzyme aromatase, subsequently blocking the production of estrogen. Since many forms of breast cancer cells are stimulated by estrogen, it is hoped that by reducing amounts of estrogen in the body the progression of such a disease can be halted. This is the basic premise behind Nolvadex®, except this drug blocks the action and not production of estrogen. The effects of Arimidex® can be quite dramatic to say the least. A daily dose of one tablet (1 mg) can produce estrogen suppression greater than 80 % in treated patients. With the powerful effect this drug has on hormone levels, it is only to be used (clinically) by post-menopausal women whose disease has progressed following treatment with Nolvadex® (tamoxifen citrate). Side effects like hot flushes and hair thinning can be present, and would no doubt be much more severe in pre-menopausal patients.
For the steroid using male athlete, Arimidex® shows great potential. Up to this point, drugs like Nolvadex® and Proviron® have been our weapons against excess estrogen. These drugs, especially in combination, do prove quite effective. But Arimidex® appears able to do the job much more efficiently, and with less hassle. Its use is only now catching on, but early reports have been excellent. A single tablet daily, the same dose use clinically, seems to be all one needs for an exceptional effect (some even report excellent results with only Y2 tablet daily). When used with strong, readily aromatizing androgens such as Dianabol or testosterone, gynecomastia and water retention can be effectively blocked. In combination with Propecia® (finasteride, see Proscar®), we have a great advance. With the one drug halting estrogen conversion and the other blocking 5-alpha reduction (testosterone, methyltestosterone and Halotestin® only), related side effects can be effectively minimized. Here the strong androgen testosterone could theoretically provide incredible muscular growth, while at the same time being as tolerable as nandrolone. Additionally the quality of the muscle should be greater, the athlete appearing harder and much more defined without holding excess water.
There are some concerns with using an aromatase inhibitor such as this during prolonged steroid treatment however. While it will effectively reduce estrogenic side effects, it will also block the beneficial properties of estrogen from becoming apparent (namely its effect on cholesterol values). Studies have clearly shown that when an aromatase inhibitor is used in conjunction with a steroid such as testosterone, suppression of HDL (good) cholesterol becomes much more pronounced. Apparently estrogen plays a role in minimizing the negative impact of steroid use. Since the estrogen receptor antagonist Nolvadex® is shown not to display an antiestrogenic effect on cholesterol values, it is certainly the preferred from of estrogen maintenance for those concerned with cardiovascular health.
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