Arimidex (ICI Australia Operations)
1 mg tablets
Indication: breast cancer
Aromatase is an enzyme involved in the synthesis of oestradiol and oestrone. By inhibiting this enzyme, anastrozole reduces the production of oestradiolin the peripheral tissues of postmenopausal women. A reduction in circulating oestradiol can be beneficial in the treatment of advanced breast cancer.
Anastrozole has been approved for use by postmenopausal women with breast cancer that has progressed following therapy with tamoxifen. In clinical trials for this indication, anastrozole has similar efficacy to megestrolacetate. Approximately one-third of patients treated with either drug will respond or have stabilisation of their disease for more than 6 months. The cancer will progress in approximately half the patients. Women rarely respond to anastrozole if they did not respond to tamoxifen or if their cancer is oestrogen-receptor negative.
The recommended daily dose is 1 mg. This is rapidly absorbed, but is eliminated slowly (half-life 50 hours). The drug is extensively metabolized with most metabolites excreted in the urine; however, no dose reduction is advised for patients with liver or kidney disease. Although anastrozole can inhibit the cytochrome P450 system, this effect occurs at higher concentrations than would be expected to occur in patients.
Adverse events during treatment are common, but many can be related to the cancer. Adverse reactions seen in trials include asthenia, nausea, headache and hot flushes.