(British Approved Name, US Adopted Name, rINN)
International Nonproprietary Names (INNs) in main languages (French, Latin, Russian, and Spanish):
Adverse Effects, Treatment, and Precautions
The most frequent adverse effects are gastrointestinal disturbances including anorexia, nausea and vomiting, and diarrhoea; asthenia; hot flushes; dizziness; drowsiness; headache; and rash. Other reported effects include hair thinning, vaginal dryness or bleeding, myalgia, arthralgia, and bone fractures, Abnormalities in liver enzyme values, thromboembolism, and increases in total cholesterol, have occurred in some patients receiving anastrozole. Very rare cases of erythema multiforme, Stevens-Johnson syndrome, and allergic reactions (including angioedema, urticaria, and anaphylaxis) have occurred.
Reductions in bone mineral density can occur during use of anastrozole. Patients with or at risk of osteoporosis should therefore have their bone density assessed at the start of therapy and at regular intervals thereafter. Treatment or prophylaxis for osteoporosis should be started as appropriate and carefully monitored. The use of anastrozole is contra-indicated in premeno-pausal women (particularly in pregnancy).
Effects on the liver. A case of acute hepatitis was attributed to anastrozole, 3 weeks after starting therapy.
Effects on the musculoskeletal system. In a series of 77 postmenopausal women treated with anastrozole for metastatic breast cancer, 12 complained of joint pains within 2 months of beginning therapy. Based on this experience and the incidence of arthralgia reported during clinical studies, the authors estimated that arthralgia occurs in 10 to 15% of patients treated with anastrozole, possibly as a result of the very low oestrogen concentrations achieved.
Adjuvant anastrozole therapy for postmenopausal women with early breast cancer was associated with accelerated bone loss, but the risk appeared to be confined to those with osteopenia at baseline. These patients should be assessed for the risk of osteoporosis before starting therapy, and the decision to treat should be made on an individual basis.
Anastrozole is rapidly and almost completely absorbed from the gastrointestinal tract after oral doses, with peak plasma concentrations within about 2 hours. Food decreases the rate of absorption, though this is not considered clinically significant. Anastrozole is 40% bound to plasma proteins. It is metabolised in the liver, and excreted in urine, chiefly as metabolites. The terminal plasma elimination half-life is about 40 to 50 hours, and steady-state concentrations are achieved after about 7 days in patients receiving once-daily doses.
Uses and Administration
Anastrozole is a potent and selective nonsteroidal inhibitor of the aromatase (oestrogen synthetase) system, which converts adrenal androgens to oestrogens in peripheral tissue. It is used in the treatment of advanced or locally advanced breast cancer, and as adjuvant treatment in early breast cancer, in postmenopausal women in an oral dose of 1 mg daily. Responses are unlikely in patients with oestrogen receptor-negative disease. Adjuvant therapy may be continued for up to 5 years, although the optimum duration is uncertain.
Endometriosis. In a small, open-label study, oral anastrozole 1 mg, given daily with a low-strength oral contraceptive for 6 months, reduced pelvic pain scores in women with refractory endometriosis. Adverse effects were mild, although most patients had breakthrough bleeding, which exacerbated pain. The authors supposed that a higher dose of oral contraceptive should be considered in future studies.
In a small pilot study of patients with rectovaginal endometriosis, anastrozole 250 micrograms was given vaginally once daily for 6 months. Dysmenorrhoea improved significantly although chronic pelvic pain was unchanged. Adverse effects were mild.
Gynaecomastia. Anastrozole has been reported to be under investigation for the treatment of gynaecomastia, but controlled studies suggest that it may be no better than placebo — see Gynaecomastia and Gynaecomastia under Adverse Effects and Precautions of Flutamide.
The symbol ¤ denotes a preparation which is discontinued or no longer actively marketed.
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