Anastrozole

Absorption

Anastrozole is rapidly absorbed and Tmax is typically reached within 2 hours of dosing under fasted conditions. Coadministration with food reduces the rate but not the overall extent of absorption - mean Cmax decreased by 16% and the median Tmax was extended to 5 hours when anastrozole was administered 30 minutes after ingestion of food, though this relatively minor alteration in absorption kinetics is not expected to result in clinically significant effects.

Toxicity

The reported oral TDLo in a human woman is 1.68 mg/kg given intermittently over the course of 12 weeks. Knowledge of the signs and symptoms of anastrozole overdose is incomplete as there are no documented descriptions of a patient receiving more than 60mg, a dose which was administered to a healthy male volunteer and was well-tolerated. There is no antidote for anastrozole and treatment should be supportive and symptomatic, including close monitoring of patient vital signs. As anastrozole exhibits relatively low protein binding, dialysis may be helpful and should be considered in select cases.

Description

Anastrozole entered its first market in the United Kingdom for the treatment of advanced breast cancer in post-menopausal women. Anastrozole is a highly potent and selective aromatase inhibitor. It is extremely potent in lowering circulating estradiol to undetectable levels in treated patients without altering other circulating hormones. The drug is reportedly well absorbed and tolerated following oral administration.

The Uses of Anastrozole

Anastrozole is a nonsteroidal inhibitor of aromatase which effectively blocks estrogen synthesis in postmenopausal women and is used as therapy of estrogen receptor positive breast cancer. Anastrozole has been associated with a low rate of serum enzyme elevations during therapy and rare instances of clinically apparent liver injury.

Background

Anastrozole is a non-steroidal aromatase inhibitor (AI), similar to letrozole, used to decrease circulating estrogen levels in the treatment of postmenopausal women with estrogen-responsive breast cancer. Aromatase inhibitors, including anastrozole, have become endocrine drugs of choice in the treatment of postmenopausal breast cancer due to a more favourable efficacy and adverse effect profile as compared to earlier estrogen receptor modulators such as tamoxifen.

Indications

Anastrozole is indicated as adjunct therapy in the treatment of hormone receptor-positive early breast cancer in postmenopausal women, and as a first-line treatment for hormone receptor-positive (or hormone receptor-unknown) locally advanced or metastatic breast cancer in postmenopausal women. It may also be used in the treatment of advanced breast cancer in postmenopausal women who experience disease progression despite treatment with tamoxifen.

What are the applications of Application

Anastrozole is a CYP19 (aromatase) inhibitor

Pharmacokinetics

Anastrozole prevents the conversion of adrenal androgens (e.g. testosterone) to estrogen in peripheral and tumour tissues. As the growth of many breast cancers is stimulated and/or maintained by the presence of estrogen, anastrozole helps to treat these cancers by decreasing the levels of circulating estrogens.
The incidence of ischemic cardiovascular events was increased during anastrozole therapy and patients with pre-existing ischemic heart disease should consider the risks and benefits of anastrozole before beginning therapy. Anastrozole has also been reported to decrease spine and hip bone mineral density (BMD), so consideration should be given to monitoring of BMD in patients receiving long-term therapy.

Metabolism

Anastrozole is primarily metabolized in the liver via oxidation and glucuronidation to a number of inactive metabolites, including hydroxyanastrozole (both free and glucuronidated) and anastrozole glucuronide. Oxidation to hydroxyanastrozole is catalyzed predominantly by CYP3A4 (as well as CYP3A5 and CYP2C8, to a lesser extent) and the direct glucuronidation of anastrozole appears to be catalyzed mainly by UGT1A4.
Anastrozole may also undergo N-dealkylation to form triazole and 3,5-Bis-(2-methylpropiononitrile)-benzoic acid. Labels for anastrozole state the main metabolite found in plasma following administration is triazole, but a recent pharmacokinetic study was unable to detect any products of N-dealkylation in vitro.

Side Effects

The side effects of Anastrozole including hot flashes, headache, bone pain, trouble sleeping, dizziness, stomach upset, nausea/vomiting, constipation, diarrhea, loss of appetite, weight gain, tiredness/weakness, increased coughing, or sore throat may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.