Arimidex (anastrozole) is a potent, nonsteroidal aromatase inhibitor specifically developed 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, depriving hormone-sensitive tumor cells of their primary growth stimulus. This targeted mechanism offers a clinically validated approach to adjuvant therapy and metastatic disease management, with demonstrated efficacy in reducing cancer recurrence and progression. Its well-established safety profile and oral administration make it a cornerstone in modern endocrine therapy regimens.

Features

• Active ingredient: Anastrozole 1 mg
• Pharmacological class: Nonsteroidal aromatase inhibitor
• Administration: Oral tablet
• Bioavailability: Approximately 80-85% following oral administration
• Half-life: 40-50 hours in postmenopausal women
• Protein binding: 40%
• Metabolism: Hepatic (85% via N-dealkylation, hydroxylation, and glucuronidation)
• Excretion: Primarily hepatic (85% fecal, 11% renal)
• FDA approval: 1995 for advanced breast cancer, 1996 for adjuvant treatment

Benefits

• Superior efficacy compared to tamoxifen in hormone receptor-positive early breast cancer, with significantly improved disease-free survival rates
• Reduced risk of recurrence by approximately 40% compared to tamoxifen in clinical trials
• Favorable side effect profile with lower incidence of thromboembolic events and endometrial cancer compared to tamoxifen
• Convenient once-daily dosing that supports treatment adherence and long-term therapy management
• Well-tolerated therapy with manageable side effects that typically don’t require treatment discontinuation
• Proven overall survival benefit in both early and advanced breast cancer settings

Common use

Arimidex is primarily indicated for the adjuvant treatment of postmenopausal women with hormone receptor-positive early breast cancer, typically administered following primary treatment with surgery and/or radiation. It is also approved for first-line treatment of advanced or metastatic hormone receptor-positive breast cancer in postmenopausal women. Additionally, Arimidex may be used as extended adjuvant therapy following initial tamoxifen treatment. Clinical practice also includes its use in neoadjuvant settings to reduce tumor size before surgery and in fertility preservation protocols for estrogen-sensitive conditions.

Dosage and direction

The recommended dosage of Arimidex is one 1 mg tablet taken orally once daily, with or without food. Treatment should continue for the duration prescribed by the healthcare provider, typically 5 years for adjuvant therapy, though extended therapy may be considered based on individual risk assessment. Tablets should be swallowed whole with water and not crushed or chewed. For patients with advanced breast cancer, treatment generally continues until disease progression or unacceptable toxicity occurs. No dosage adjustment is required for elderly patients or those with mild to moderate hepatic impairment, but caution is advised in severe hepatic impairment.

Precautions

Patients should undergo comprehensive bone density assessment before initiating therapy and at regular intervals during treatment due to Arimidex’s potential to accelerate bone mineral density loss. Regular monitoring of lipid profiles is recommended as aromatase inhibitors may affect cholesterol metabolism. Patients should be advised about potential effects on cognitive function and mood changes. Caution is warranted in patients with pre-existing cardiac conditions or risk factors, as long-term estrogen suppression may impact cardiovascular health. Ophthalmologic examinations are advisable due to potential visual disturbances. Patients should be monitored for symptoms of carpal tunnel syndrome and musculoskeletal disorders.

Contraindications

Arimidex is contraindicated in premenopausal women, pregnant women, and nursing mothers due to potential fetal harm and interference with estrogen-dependent developmental processes. It should not be used in patients with known hypersensitivity to anastrozole or any component of the formulation. Concomitant use with estrogen-containing therapies is contraindicated as they would counteract Arimidex’s therapeutic effect. The medication is not indicated for use in pediatric patients. Patients with severe hepatic impairment (Child-Pugh Class C) should generally avoid Arimidex due to limited safety data in this population.

Possible side effects

Very common (≥10%): Hot flashes (35%), asthenia/fatigue (19%), arthritis/arthralgia (11-35%), mood disturbances (19%), nausea (11-19%), headache (13%), pain (14%), back pain (12%), osteoporosis (11%), peripheral edema (10%)

Common (1-10%): Depression (13%), insomnia (11%), hypertension (13%), rash (11%), vomiting (8%), constipation (8%), diarrhea (8%), weight gain (9%), hypercholesterolemia (9%), carpal tunnel syndrome (6%)

Uncommon (0.1-1%): Venous thromboembolic events, ischemic cerebrovascular events, vaginal bleeding, allergic reactions, hepatitis, trigger finger

Rare (<0.1%): Stevens-Johnson syndrome, anaphylaxis, erythema multiforme

Drug interaction

Arimidex demonstrates minimal cytochrome P450 interactions but may be affected by potent enzyme inducers or inhibitors. Estrogen-containing therapies (including HRT) significantly reduce Arimidex’s efficacy and should be avoided. Tamoxifen co-administration reduces anastrozole plasma concentrations by 27% and is not recommended. CYP3A4 inducers (rifampicin, phenytoin, carbamazepine) may decrease anastrozole concentrations. Although formal interaction studies are limited, caution is advised with drugs that affect liver metabolism. No clinically significant interactions have been observed with warfarin, though monitoring is prudent when initiating combined therapy.

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 never take two doses simultaneously to make up for a missed dose. Consistency in dosing is important for maintaining stable estrogen suppression, but occasional missed doses are unlikely to significantly impact overall treatment efficacy. Patients should maintain a regular dosing routine and consider using pill organizers or reminder systems to support adherence.

Overdose

There is limited experience with Arimidex overdose. Single doses up to 60 mg have been administered without serious adverse effects. Expected manifestations would likely include enhanced pharmacological effects such as increased hot flashes, nausea, and dizziness. No specific antidote exists; treatment should be symptomatic and supportive. Gastric lavage may be considered if ingestion occurred within a short timeframe. Vital signs should be monitored, and appropriate supportive care provided based on clinical presentation. Dialysis is unlikely to be beneficial due to Arimidex’s high protein binding and extensive tissue distribution.

Storage

Store Arimidex tablets at controlled room temperature (20-25°C or 68-77°F) with excursions permitted between 15-30°C (59-86°F). Keep in the original container with the lid tightly closed to protect from moisture and light. Do not store in bathroom cabinets where humidity levels may fluctuate. Keep out of reach of children and pets. Do not use tablets beyond the expiration date printed on the packaging. Proper disposal of unused medication should follow local regulations, typically through medication take-back programs rather than flushing or household trash.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Individual patient responses to Arimidex may vary, and treatment decisions should be made in consultation with a qualified healthcare professional familiar with the patient’s complete medical history. The prescribing physician should be the ultimate authority regarding appropriate use, dosage, and duration of therapy. Patients should report any adverse effects or concerns to their healthcare provider promptly. This information is not exhaustive and may not include all possible uses, directions, precautions, or interactions.

Reviews

Clinical studies demonstrate Arimidex’s consistent efficacy profile, with the ATAC trial showing a 24% reduction in recurrence risk compared to tamoxifen at 10-year follow-up. The BIG 1-98 trial confirmed superior disease-free survival with Arimidex monotherapy versus tamoxifen. Real-world evidence supports trial findings, with most patients tolerating therapy well despite manageable side effects. Many oncologists consider Arimidex a first-choice adjuvant endocrine therapy based on its proven efficacy and generally favorable tolerability profile compared to other endocrine agents. Patient-reported outcomes indicate high satisfaction with treatment efficacy despite common side effects like arthralgia and hot flashes.