Medical uses: The ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial was an international randomised controlled trial of 9366 women with localized breast cancer who received either anastrozole, tamoxifen, or both for five years, followed by five years of follow-up. After more than 5 years the group that received anastrozole had significantly better clinical results than the tamoxifen group. The trial suggested that anastrozole is the preferred medical therapy for postmenopausal women with localized breast cancer that is estrogen receptor (ER) positive. Another study found that the risk of recurrence was reduced 40%, which also included an increased risk of bone fractures, and that ER negative patients benefited from switching to anastrozole.
Mechanism of action: Anastrozole binds reversibly to the aromatase enzyme through competitive inhibition, inhibits the conversion of androgens to estrogens in peripheral tissues (outside the CNS), and a few CNS sites in various regions within the brain.
Side effects: Bone weakness has been associated with anastrozole. Women who switched to anastrozole after two years on tamoxifen reported twice as many fractures as those who continued to take tamoxifen (2.1% compared to 1%). Bisphosphonates are sometimes prescribed to prevent the osteoporosis induced by aromatase inhibitors. The level of circulating oestradiol is likely causal here and not the anastrozole itself, and so the dose will determine likelihood of osteoporosis (oestradiol inhibits osteoclasts, which resorb bone).
Usage in men: Anastrozole has been tested for reducing estrogens, including estradiol, in men. Excess estradiol in men can cause benign prostatic hyperplasia, gynecomastia, and symptoms of hypogonadism. It can also contribute to increased risk of stroke, heart attack, chronic inflammation, prostate enlargement and prostate cancer. Some athletes and body builders will also use anastrozole as a part of their steroid cycle to reduce and prevent symptoms of excess estrogens; gynecomastia and water retention. Study data suggests dosages of 0.5 mg to 1 mg a day reduce serum estradiol approx. 50% in men, which differs in postmenopausal women.
Usage in children: Anastrozole may be used off-label in children with precocious puberty, or children with pubertal gynecomastia. Following the onset of puberty, the epiphyseal plate begins to close due to an increased amount of estrogen production escaping local metabolism and spreading to the circulatory system. It is shown to help slow this process, and increase adult height prediction in adolescent males treated with protein-based peptide hormones for the treatment of growth hormone deficiency.
Chemical synthesis: The synthesis begins with nucleophilic substitution of two benzylic bromides in α,α'-dibromomesitylene (prepared by radical bromination of mesitylene, not shown on the scheme) with cyanide by treatment with potassium cyanide under phase transfer conditions, affording the dinitrile. Exhaustive methylation with methyl iodide and sodium hydride leads to the replacement of the more acidic side chain hydrogen atoms by methyl groups. The treatment with bromine in the presence of benzoyl peroxide leads to the formation of the corresponding benzyl bromide. Reaction of that product with 1,2,4-triazole in the presence of a base completes the synthesis of the aromatase inhibitor.