Anastrozole (Arimidex)
Triazole-class non-steroidal aromatase inhibitor (AI). FDA-approved (1995 AstraZeneca) for postmenopausal ER+ breast cancer. AAS-cycle E2-control golden-standard, 0.25-1 mg EOD-2x/week titrated by bloodwork.
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Related comparisons
Anastrozol vs Letrozol vs ExemestaneWHAT IS ANASTROZOLE (ARIMIDEX)?
Detailed overview
Anastrozole (Arimidex) is a third-generation non-steroidal aromatase inhibitor (AI) of the triazole class developed by AstraZeneca (then Zeneca) and approved by the FDA in 1995 for adjuvant treatment of postmenopausal ER+ breast cancer. The ATAC trial (Buzdar 2002, PMID 12081816) demonstrated approximately 97% serum estradiol suppression at 1 mg/day through reversible competitive inhibition of the enzyme – anastrozole binds the heme group of CYP19 aromatase, blocking conversion of androgens to estrogens. In AAS context, it is the standard E2-control agent during testosterone-base cycles (Test/Tren/Mast/Dianabol): weekly dosing is bloodwork-titrated, with E2 trough target 20-30 pg/mL measured by LC-MS/MS sensitive assay (NOT ECL – ECL overestimates E2 at low levels, leading to falsely elevated readings, unnecessary anastrozole dosing, and crashed E2). Anastrozole is the AAS-PCT golden-standard among aromatase inhibitors: well documented, relatively easy to titrate, moderate lipid impact.
Mechanism
Reversible non-steroidal CYP19 aromatase inhibitor, ~97% serum E2 suppression at 1 mg/day
Dosing (AAS)
0.25-1 mg EOD-2x/week titrated by bloodwork (E2 trough 20-30 pg/mL LC-MS/MS)
Half-life
~50 hours (single daily dose, steady-state day 7)
Onset
E2 reduction measurable 24-48 h, full effect 5-7 days
Legal status
FDA + EMA Rx, HU + PL approved, WADA S4.1 banned
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 7
- Joint and muscle pain (arthralgia, myalgia), a common AI side effect, especially wrists, knees and hands, pronounced when E2 is over-suppressed
- Excessive estrogen suppression (crashed E2): loss of libido, erectile dysfunction, lethargy, depressed mood, sleep disturbance
- Adverse lipid profile: HDL decrease (~10-20%) and LDL rise, long-term cardiovascular risk, lipid monitoring required
- Reduced bone mineral density (osteopenia, osteoporosis) and fracture risk from chronic E2 deficit, DEXA monitoring advised with long-term use
- Hot flushes and sweating, a characteristic vasomotor symptom of estrogen suppression (common in clinical trials)
- Fatigue, headache and nausea; rarely mild, transient ALT/AST elevation (<2% incidence, serious hepatotoxicity extremely rare)
- Skin rash and rarely severe skin reactions (erythema multiforme, Stevens-Johnson syndrome described on the FDA label), allergic reactions
Contraindications · 7
- Pregnancy and breastfeeding are absolute contraindications (FDA Pregnancy Category X) – risk of fetal harm and pregnancy loss, contraception mandatory in women of childbearing potential
- Premenopausal women: anastrozole is ineffective and not indicated, as ovarian aromatase activity is not adequately suppressed, causing hormonal dysfunction
- Known hypersensitivity to anastrozole or any excipient (allergic reaction)
- Severe hepatic insufficiency (Child-Pugh C): CYP3A4/CYP1A2 metabolism is impaired, clinical data lacking, avoid
- Pre-existing osteoporosis or severe bone loss: chronic E2 suppression further worsens bone density and raises fracture risk
- Concurrent tamoxifen or estrogen-containing agents: tamoxifen lowers anastrozole plasma levels and estrogens negate the treatment, combination should be avoided
- Significantly adverse cardiovascular/lipid status (ischaemic heart disease, uncontrolled dyslipidemia): the AI can further worsen the lipid profile, close monitoring or avoidance warranted
Related Performance Compounds
Same therapeutic category
Studies
Related research and clinical findings
Meta-analyses of phase 3 randomised controlled trials of third generation aromatase inhibitors versus tamoxifen as first-line endocrine therapy in postmenopausal women with hormone receptor-positive advanced breast cancer.
Robertson JFR, Paridaens RJ, Lichfield J, Bradbury I, Campbell C
Influence of letrozole and anastrozole on total body aromatization and plasma estrogen levels in postmenopausal breast cancer patients evaluated in a randomized, cross-over study.
Geisler J, Haynes B, Anker G, Dowsett M, Lønning PE
An integrated view of aromatase and its inhibition.
Miller WR, Anderson TJ, Evans DB
Aromatase inhibitor mechanism: review
Brueggemeier RW, Hackett JC, Diaz-Cruz ES.
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