Incorrect. Both the dosage as well as the EOD reccomendation are incorrect.
First, regarding the reccomendation of "1.25
mg" it's way too much. You can use 100
mcgs/day for maximum inhibition of aromatase:
J Clin Endocrinol Metab. 1995 Sep;80(9):2658-60.
Use of ultrasensitive recombinant cell bioassay to measure estrogen levels in women with breast cancer receiving the aromatase inhibitor, letrozole.
Klein KO, Demers LM, Santner SJ, Baron J, Cutler GB Jr, Santen RJ.
Children's Hospital of Orange County, California 92668, USA.
The development of well tolerated, potent, specific, and nontoxic aromatase inhibitors for the treatment of postmenopausal women with estrogen-dependent breast cancer has been a major goal of recent studies. The third generation inhibitors now under investigation are nearly 10,000-fold more potent than first generation compounds. Currently available RIAs for plasma estradiol lack sufficient sensitivity to measure levels during aromatase inhibition and, thus, to assess drug potency precisely. The availability of an ultrasensitive bioassay for estradiol provided the opportunity to accurately assess the potency of a new third generation triazole aromatase inhibitor, letrozole (CGS 20267). We used this assay to measure estradiol levels in 14 women with metastatic breast cancer given letrozole at doses of 100 micrograms to 5.0 mg/day over a 12-week period. The lack of differences between doses and sampling times allowed pooling of data. Basal estradiol levels of 7.2 +/- 1.9 pmol/L (mean +/- SEM, 1.95 +/- 0.52 pg/mL) fell to 0.26 +/- 0.11 pmol/L (0.07 +/- 0.03 pg/mL) during the first 6 weeks of therapy and to 0.48 +/- 0.18 pmol/L (0.13 +/- 0.05 pg/mL) during the second 6 weeks of therapy. Although plasma estradiol levels measured by RIA were significantly correlated with levels measured by bioassay (r = 0.79; P < 0.01), the degree of suppression assessed by the bioassay (95 +/- 2% after 6 weeks) was greater than that determined by the RIA (81 +/- 4%), presumably due to improved ability to measure very low estradiol levels. We conclude that plasma estradiol is suppressed by letrozole to lower levels than previously observed, with equivalent suppression at all doses studied. A slight, although not statistically significant, rebound in estradiol levels occurs during the second 6 weeks of therapy compared to the first 6 weeks.
Maximum inhibition of aromatase is achieved at letrozole doses as low as 100 micrograms.
Now, with regards to the "EOD" reccomendation, letrozole has a very long 1/2 life, and if you want to ever achieve a steady-state plasma level of it, you need to take a daily dose of it, and even then, it takes a month at .5mgs/day to two months at 2.5mgs/day in order to achieve a constant level of it in your blood. It stands to reason every other day dosing, (especially at 1.25mgs/EOD) would make it difficult to get a steady level of it in your blood, reflective of the accumulation that occurs with letrozole over long-term dosing :
Double-blind, randomised, multicentre endocrine trial comparing two letrozole doses, in postmenopausal breast cancer patients.
Bajetta E,
Zilembo N,
Dowsett M,
Guillevin L,
Di Leo A,
Celio L,
Martinetti A,
Marchiano A,
Pozzi P,
Stani S,
Bichisao E.
Division of Medical Oncology B, Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy.
Letrozole is an orally competitive aromatase inhibitor. This double-blind, randomised, multicentre trial was carried out to evaluate the endocrine effects of two doses of letrozole, 0.5 mg versus 2.5 mg orally daily, in postmenopausal advanced breast cancer patients progressing after tamoxifen. The pharmacokinetics of letrozole was also assessed. 46 patients entered the trial, 22 on letrozole 0.5 mg and 24 on 2.5 mg. A significant suppression of oestrone and oestradiol levels was achieved by both letrozole doses. Neither letrozole dose induced any changes in cortisol and aldosterone production at rest or after Synacthen stimulation. Androstenedione, testosterone, 17 alpha-OH progesterone, triiodothyronine (T3) thyroxine, (T4) and thyroid-stimulating hormone (TSH) plasma levels did not show any significant changes. Sex hormone binding globulin (SHBG), follicle-stimulating hormone (FSH) and luteinising hormone (LH) levels increased significantly over time.
Plasma letrozole concentrations increased until reaching steady-state values after 1 month at the dose of 0.5 mg and after 2 months at 2.5 mg. In conclusion, both letrozole doses suppressed oestrogen levels without affecting adrenal activity.
