Pharmacological and clinical profile of anastrozole.


Anastrozole (Arimidex, 2,-2[5-(1H-1,2,4-triazol-1-ylmethyl)-1,3-phenylene]bis(2-met hyl)propiononitrile) is a novel, potent aromatase inhibitor belonging to the triazole class. In vitro and in vivo animal studies have revealed the drug to be a potent inhibitor of the aromatase enzyme with no inhibitory activity versus other enzymes involved in steroid synthesis. The drug is a potent suppressor of plasma estrogens in healthy male and postmenopausal female volunteers as well as postmenopausal breast cancer patients, and anastrozole administered as 1 mg or 10 mg daily has been shown to inhibit in vivo aromatization by 96.7 and 98.1%, respectively. Two large, randomized studies revealed anastrozole to cause objective response rates and stable disease comparable to what was achieved with megestrol acetate but with a lower incidence of side effects. While follow-up results have not revealed any significant difference in time to relapse between the drug regimens, they have revealed an improved survival among patients treated with anastrozole 1 mg compared to megestrol acetate 160 mg daily. Further follow-up is required to finally decide whether there may be a survival benefit also among patients treated with anastrozole 10 mg daily and to evaluate whether the improvement in survival is associated with an improved disease-free survival as would be anticipated.

As an aromatase inhibitor, Arimidex's mechanism of action -- blocking conversion of aromatizable steroids to estrogen -- is in contrast to the mechanism of action of anti-estrogens such as clomiphene (Clomid®) or tamoxifen (Nolvadex®) , which block estrogen receptors in some tissues, and activate estrogen receptors in others. During a cycle, if using Arimidex, there is generally no need to use Clomid as well, but there may still be benefits to doing so.