Letrozole

[Da Bull]

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DESCRIPTION

Femara (letrozole tablets) for oral administration contain 2.5 mg of letrozole, a nonsteroidal aromatase inhibitor (inhibitor of estrogen synthesis). It is chemically described as 4,4'-(1H-1,2,4 -Triazol-1-ylmethylene) dibenzonitrile.

Letrozole is a white to yellowish crystalline powder, practically odorless, freely soluble in dichloromethane, slightly soluble in ethanol, and practically insoluble in water. It has a molecular weight of 285.31, empirical formula C17H11N5 and a melting range of 184o C-185o C.

Femara (letrozole tablets) is available as 2.5 mg tablets for oral administration.

Inactive Ingredients.

Colloidal silicon dioxide, ferric oxide, hydroxypropyl methylcellulose, lactose monohydrate, magnesium stearate, maize starch, microcrystalline cellulose, polyethylene glycol, sodium starch glycolate, talc, and titanium dioxide.



CLINICAL PHARMACOLOGY

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.


SIDE EFFECTS

Femara (letrozole tablets) was generally well tolerated in two controlled clinical trials. Study discontinuations in the megestrol acetate comparison study for adverse events other than progression of tumor occurred in 5/188 (2.7%) of patients on Femara 0.5 mg, in 4/174 (2.3%) of the patients on Femara 2.5 mg, and in 15/190 (7.9%) of patients on megestrol acetate. There were fewer thromboembolic events at both Femara doses than on the megestrol acetate arm (2 of 362 patients or 0.6% vs. 9 of 190 patients or 4.7%). There was also less vaginal bleeding (1 of 362 patients or 0.3% vs. 6 of 190 patients or 3.2%) on letrozole than on megestrol acetate. In the aminoglutethimide comparison study, discontinuations for reasons other than progression occurred in 6/193 (3.1%) of patients on 0.5 mg Femara, 7/185 (3.8%) of patients on 2.5 mg Femara, and 7/178 (3.9%) of patients on aminoglutethimide.

Comparisons of the incidence of adverse events revealed no significant differences between the high and low dose Femara groups in either study. Most of the adverse events observed in all treatment groups were mild to moderate in severity and it was generally not possible to distinguish adverse reactions due to treatment from the consequences of the patient’s metastatic breast cancer, the effects of estrogen deprivation, or intercurrent illness.


DRUG INTERACTIONS

Clinical interaction studies with cimetidine and warfarin indicated that the coadministration of Femara with these drugs does not result in clinically- significant drug interactions. (See CLINICAL PHARMACOLOGY)

There is no clinical experience to date on the use of Femara in combination with other anti- cancer agents.

Drug/Laboratory Test-Interactions

None observed.

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