ARIMIDEX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ARIMIDEX (ARIMIDEX).
Aromatase inhibitor; inhibits conversion of androgens to estrogens by binding to aromatase enzyme, reducing estrogen levels in tissues.
| Metabolism | Hepatic via CYP3A4; extensive metabolism to inactive metabolites (triazole, anastrozole glucuronide); <10% excreted unchanged in urine. |
| Excretion | Primarily hepatic metabolism via N-dealkylation and glucuronidation; ~80% excreted in feces, <10% unchanged in urine. |
| Half-life | Terminal elimination half-life ~50 hours (range 30-60 hours); supports once-daily dosing. |
| Protein binding | 98-99% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Approximately 93 L (1.3 L/kg for 70 kg human); extensive extravascular distribution. |
| Bioavailability | Oral bioavailability ~80%; not significantly affected by food. |
| Onset of Action | Oral: Estradiol suppression within 24 hours, maximal suppression by 3-4 days. |
| Duration of Action | Estradiol suppression persists for ~6 days after last dose; clinical effect on tumor growth over weeks. |
| Action Class | Aromatase inhibitor |
| Brand Substitutes | Aromita Tablet, Femistra Tablet, Anastronat 1mg Tablet, Femitraz Tablet |
1 mg orally once daily
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for GFR ≥30 mL/min. No data for GFR <30 mL/min; use with caution. |
| Liver impairment | Mild hepatic impairment (Child-Pugh A): no adjustment. Moderate to severe (Child-Pugh B or C): not recommended due to lack of data. |
| Pediatric use | Not approved for use in pediatric patients. |
| Geriatric use | No specific dose adjustment required; same as adult dosing (1 mg once daily). Monitor renal function as part of standard care. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ARIMIDEX (ARIMIDEX).
| Breastfeeding | Contraindicated during breastfeeding. No human data on excretion into breast milk; M/P ratio unknown. Potential for serious adverse effects in nursing infants due to aromatase inhibition. |
| Teratogenic Risk | Pregnancy Category D. Anastrozole is contraindicated in pregnancy. First trimester: Risk of fetal harm due to aromatase inhibition; potential for developmental abnormalities based on animal studies. Second and third trimesters: Continued risk of fetal androgen deprivation; may affect sexual differentiation. Adequate contraception required during therapy. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to anastrozole or excipients; premenopausal women; pregnancy; lactation.
| Precautions | Ischemic cardiovascular events (angina, MI); bone demineralization/osteoporosis with increased fracture risk; elevated liver enzymes; anaphylaxis; Stevens-Johnson syndrome; reduced bone mineral density; caution in patients with severe hepatic impairment. |
| Food/Dietary | No significant food interactions. May be taken with or without food. Grapefruit juice has no known interaction. Avoid alcohol if liver dysfunction is present. |
| Clinical Pearls |
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| Fetal Monitoring |
| Pregnancy test prior to initiation and periodically during therapy. Monitor for signs of pregnancy. If pregnancy occurs during treatment, immediate discontinuation and fetal assessment recommended. |
| Fertility Effects | Reversible effects on female fertility based on animal studies; in humans, ovarian suppression and reduced fertility may occur. Anastrozole is used off-label for ovulation induction, indicating complex fertility effects. |
| Arimidex (anastrozole) is an aromatase inhibitor used in hormone receptor-positive breast cancer. It is not effective in estrogen receptor-negative tumors. Monitor bone mineral density due to increased fracture risk. Use with caution in patients with pre-existing osteoporosis. Contraindicated in premenopausal women unless used with a GnRH agonist. Renal impairment does not require dose adjustment, but hepatic impairment may require monitoring. |
| Patient Advice | Take Arimidex exactly as prescribed, usually once daily with or without food. · Do not take Arimidex if you are pregnant or breastfeeding; use effective non-hormonal contraception. · Report new or worsening bone pain, joint stiffness, or fractures to your healthcare provider. · This medication does not work in estrogen receptor-negative breast cancer; confirm receptor status with your doctor. · Avoid alcohol if you have liver problems; consult your doctor about alcohol use. · Do not stop taking Arimidex without consulting your doctor, even if you feel well. · Inform your doctor of all medications you take, including over-the-counter drugs and supplements. |