Arimidex (anastrozole) is a potent, non-steroidal aromatase inhibitor specifically formulated for the treatment of hormone receptor-positive early and advanced breast cancer in postmenopausal women. By selectively inhibiting the aromatase enzyme, Arimidex significantly reduces estrogen production, a key driver in approximately 75% of breast cancer cases. This targeted mechanism offers a sophisticated endocrine therapy option with a well-established efficacy and safety profile, making it a cornerstone in modern oncology practice for appropriate patient populations.

Features

• Active ingredient: Anastrozole 1 mg
• Pharmaceutical class: Non-steroidal aromatase inhibitor
• Administration: Oral tablet formulation
• Bioavailability: Approximately 83-85% following oral administration
• Half-life: 40-50 hours in postmenopausal women
• Metabolism: Hepatic (85% via N-dealkylation, hydroxylation, and glucuronidation)
• Excretion: Primarily hepatic (85% fecal, 11% renal)
• FDA approval: 1995 for advanced breast cancer, 2002 for adjuvant treatment
• Pregnancy category: X (contraindicated in pregnancy)

Benefits

• Superior disease-free survival compared to tamoxifen in hormone receptor-positive early breast cancer
• Reduced risk of contralateral breast cancer development
• Avoidance of tamoxifen-associated thromboembolic events and endometrial cancer risk
• Favorable side effect profile with manageable estrogen-depletion symptoms
• Once-daily dosing regimen for optimal patient compliance
• No requirement for corticosteroid supplementation unlike earlier aromatase inhibitors

Common use

Arimidex is primarily indicated for the adjuvant treatment of postmenopausal women with hormone receptor-positive early breast cancer following primary surgical intervention. It is also approved for first-line treatment of hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer in postmenopausal women. Additionally, Arimidex is used in the extended adjuvant setting following initial tamoxifen therapy and for treatment of advanced breast cancer that has progressed following tamoxifen therapy. Clinical practice also includes off-label use in estrogen suppression for fertility treatments and gynecomastia prevention, though these applications require careful risk-benefit assessment.

Dosage and direction

The recommended dosage of Arimidex is one 1 mg tablet taken orally once daily, with or without food. For adjuvant treatment of early breast cancer, therapy should continue for 5 years unless disease recurrence or unacceptable toxicity occurs. Patients with advanced breast cancer should continue treatment until tumor progression is documented. Tablets should be swallowed whole with water; crushing or chewing is not recommended. No initial dosage adjustment is necessary for elderly patients or those with mild to moderate hepatic impairment. For patients with severe hepatic impairment, careful monitoring is advised though formal dosage recommendations are not established.

Precautions

Patients should undergo comprehensive bone mineral density assessment before initiating therapy and at regular intervals during treatment due to accelerated bone loss associated with estrogen suppression. Regular monitoring of lipid profiles is recommended as aromatase inhibitors may adversely affect cholesterol levels. Hepatic function should be assessed periodically, particularly in patients with pre-existing liver conditions. Patients should be advised about potential effects on cognitive function and mood changes. Caution is warranted in patients with pre-existing osteoporosis or risk factors for fracture. Vitamin D and calcium supplementation, along with weight-bearing exercise, are generally recommended to mitigate bone health concerns.

Contraindications

Arimidex is contraindicated in premenopausal women, pregnant women, and nursing mothers due to potential fetal harm and interference with estrogen-dependent developmental processes. The medication is contraindicated in patients with known hypersensitivity to anastrozole or any component of the formulation. Concomitant use with estrogen-containing therapies is contraindicated as these agents would counteract the therapeutic effect. Patients with severe hepatic impairment (Child-Pugh Class C) should generally avoid use unless potential benefits outweigh risks under close supervision. The medication is not indicated for use in pediatric populations.

Possible side effects

The most frequently reported adverse reactions (≥10%) include hot flashes (35%), asthenia (16%), arthritis/arthralgia (11-35%), pain (11-14%), pharyngitis (12%), and nausea (11%). Less common but clinically significant side effects include vaginal dryness (1-9%), mood disturbances (1-9%), insomnia (1-9%), and headache (1-9%). Serious adverse reactions may include cardiovascular events (2-4%), fractures (2-11%), and carpal tunnel syndrome (2-5%). Laboratory abnormalities may include elevated gamma-glutamyl transferase (5-7%), cholesterol increases (2-9%), and decreased bone mineral density. Most side effects are mild to moderate in severity and often diminish with continued therapy.

Drug interaction

Arimidex is primarily metabolized by CYP3A4 and UGT1A4 enzymes, though it does not significantly inhibit major CYP enzymes. Concomitant use with strong CYP3A4 inducers (rifampicin, phenytoin, carbamazepine) may decrease anastrozole concentrations, potentially reducing efficacy. Tamoxifen co-administration reduces anastrozole plasma concentrations by 27% and is not recommended. Estrogen-containing therapies antagonize the pharmacological effect and should be avoided. No clinically significant interactions have been observed with warfarin, though monitoring is prudent. The effect of other medications metabolized by CYP1A2, 2C8, 2C9, 2D6, or 3A4 is not expected to be significant.

Missed dose

If a dose is missed, patients should take it as soon as remembered unless it is nearly time for the next scheduled dose. In that case, the missed dose should be skipped, and the regular dosing schedule resumed. Patients should not double the dose to make up for a missed administration. Consistent daily dosing is important for maintaining stable estrogen suppression, though occasional missed doses are unlikely to significantly impact overall efficacy given the drug’s long half-life. Healthcare providers should be notified if multiple doses are missed consecutively.

Overdose

Limited data exist regarding Arimidex overdose in humans. Single doses up to 60 mg have been administered without significant adverse effects. In animal studies, doses up to 200 mg/kg in mice and 100 mg/kg in rats produced minimal toxicity. No specific antidote exists for anastrozole overdose. Management should include general supportive measures and symptomatic treatment. Gastric lavage may be considered if ingestion occurred within a short time frame. Given the drug’s extensive protein binding, dialysis is unlikely to be effective. Medical supervision is recommended for any suspected overdose situation.

Storage

Arimidex tablets should be stored at controlled room temperature (20-25°C or 68-77°F) with excursions permitted between 15-30°C (59-86°F). Tablets should be kept in their original container with the lid tightly closed to protect from moisture and light. The medication should be kept out of reach of children and pets. Unused medication should be properly disposed of according to local regulations, preferably through medication take-back programs. Tablets should not be used beyond the expiration date printed on the packaging.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Individual patient responses to Arimidex may vary based on numerous factors including genetic makeup, concomitant medications, and overall health status. Treatment decisions should be made in consultation with a qualified healthcare professional who can assess individual risk-benefit considerations. The prescribing physician should be the ultimate source of information regarding appropriate use, dosing, and monitoring for this medication. Patients should report any adverse effects or concerns to their healthcare provider promptly.

Reviews

Clinical trials and post-marketing surveillance demonstrate consistent efficacy with 86.9% of patients completing 5 years of adjuvant therapy in the ATAC trial. Oncologists report generally favorable patient tolerance with manageable side effects. Patient-reported outcomes indicate that while vasomotor symptoms and joint pain can affect quality of life, most women consider the cancer protection benefits worthwhile. Long-term follow-up data from multiple studies confirm sustained reduction in recurrence risk with appropriate management of bone health and lipid parameters. The medication receives high marks from clinicians for its predictable pharmacokinetics and well-characterized safety profile compared to earlier endocrine therapies.