- Aromatase Inhibitors
VA Class: AN900
Chemical Name: α,α,α′,α′-Tetramethyl-5-(1H-1,2,4-triazol-1-ylmethyl)-1,3-benzenediacetonitrile
Molecular Formula: C17H19N5
CAS Number: 120511-73-1
Medically reviewed by Drugs.com. Last updated on Jan 11, 2021.
Uses for Anastrozole
Early-stage Breast Cancer in Postmenopausal Women
Aromatase inhibitors are a treatment of choice for adjuvant hormonal therapy to lower risk of breast cancer recurrence in postmenopausal women with early-stage hormone receptor-positive breast cancer.20 61 An aromatase inhibitor-containing regimen is modestly more effective than tamoxifen alone.20 61
ASCO states that most postmenopausal women with early-stage hormone receptor-positive breast cancer should consider receiving an aromatase inhibitor during the course of adjuvant therapy, either as primary (initial) therapy or following 2–3 years of tamoxifen (sequential therapy), for a total of 5 years of adjuvant endocrine therapy.61 Data also support switching to an aromatase inhibitor following 5 years of adjuvant tamoxifen (extended adjuvant therapy).61 ASCO states that women who receive extended adjuvant therapy should receive tamoxifen for 5 years followed by an aromatase inhibitor for 3–5 years.61
Consider adverse effects, patient preference, and preexisting conditions when selecting an adjuvant regimen.61 Joint disorders (arthritis, arthrosis, arthralgia), fractures, and elevated cholesterol reported more frequently in patients receiving adjuvant anastrozole,1 whereas adverse gynecologic effects (endometrial cancer, vaginal discharge, vaginal bleeding), hot flushes, ischemic cerebrovascular events, and venous thromboembolism reported more frequently in those receiving adjuvant tamoxifen.1 50
Early-stage Breast Cancer in Premenopausal Women
Use of endocrine therapy (i.e., anastrozole, exemestane, letrozole, tamoxifen) in combination with ovarian suppression† as adjuvant therapy in premenopausal women† with early-stage hormone receptor-positive breast cancer may be considered a reasonable choice (accepted).10010 10011 10012 10013 10023 10026 10028
Advanced Breast Cancer in Postmenopausal Women
First-line therapy for hormone receptor-positive (i.e., estrogen receptor-positive, progesterone receptor-positive, or both) or hormone receptor-unknown locally advanced or metastatic breast cancer in postmenopausal women.1 15 20
Second-line therapy for advanced breast cancer in postmenopausal women with disease progression following tamoxifen therapy.1 20 Usually ineffective in patients with estrogen receptor-negative breast cancer and those who fail tamoxifen therapy.1
Reduction in the Incidence of Breast Cancer in Women at High Risk
Anastrozole Dosage and Administration
Administer orally once daily without regard to meals.1
Adjuvant Therapy for Early-stage Breast Cancer in Postmenopausal WomenOral
1 mg once daily.1
Initial adjuvant therapy: Optimum duration unknown; duration of therapy in clinical study was 5 years.1 In patients who discontinue aromatase inhibitor therapy prior to 5 years, ASCO recommends consideration of tamoxifen to complete the 5-year adjuvant regimen.61
Sequential adjuvant therapy†: Optimal time to switch from tamoxifen to aromatase inhibitor therapy is unknown.61 ASCO states that disease-free patients may switch to an aromatase inhibitor after 2–3 years of adjuvant tamoxifen therapy to complete a 5-year sequential adjuvant regimen.61
Extended adjuvant therapy†: ASCO recommends that patients who receive an extended adjuvant regimen receive an aromatase inhibitor (e.g., anastrozole) for 3–5 years beyond the initial 5 years of tamoxifen therapy, to complete a total of 8–10 years of adjuvant endocrine therapy.61
Adjuvant Therapy for Early-stage Breast Cancer in Premenopausal Women†Oral
In clinical studies, ovarian suppression achieved with goserelin 3.6 mg implanted sub-Q every 4 weeks, leuprolide acetate 3.75 mg by IM injection every 4 weeks, triptorelin 3.75 mg by IM injection every 4 weeks, or surgical or radiation ablation.10010 10011 10012 10013 10023 10026
First-line Therapy for Advanced Breast Cancer in Postmenopausal WomenOral
Second-line Therapy for Advanced Breast Cancer in Postmenopausal WomenOral
Adjuvant Treatment of Early-stage Breast Cancer in Postmenopausal WomenOral
Maximum 5 years of aromatase inhibitor therapy; toxicity beyond 5 years not established.61
Dosage adjustment not required in patients with mild to moderate hepatic impairment or stable hepatic cirrhosis.1 (See Special Populations under Pharmacokinetics.)
Not studied in patients with severe hepatic impairment.1
Dosage adjustment not required.1 (See Special Populations under Pharmacokinetics.)
Dosage adjustment not required.1 (See Special Populations under Pharmacokinetics.)
Cautions for Anastrozole
Known hypersensitivity to anastrozole or any ingredient in the formulation.1
Ischemic Cardiovascular Effects
Increased incidence of ischemic cardiovascular events (e.g., angina pectoris) reported in patients with preexisting ischemic heart disease; consider risks and benefits of therapy in these patients.1
Effects on Bone
Postmenopausal women receiving an aromatase inhibitor as adjuvant therapy are at high risk for osteoporosis.36
Bone mineral density (BMD) at lumbar spine and hip decreased in patients receiving anastrozole and increased in those receiving tamoxifen as initial (primary) adjuvant therapy.1 43 48 Incidence of fractures was higher with anastrozole versus tamoxifen during treatment, but not following completion of treatment.1 66
Evaluate all postmenopausal women initiating adjuvant aromatase inhibitor therapy for risk of osteoporotic fractures;70 71 73 74 determine BMD and assess other risk factors for fracture (e.g., age, low body mass index, family history of hip fracture, prior fragility fracture, history of cigarette smoking, excessive alcohol consumption, current or prior corticosteroid use).70 71 73 74 Closely monitor patients for changes in risk status during therapy, and assess BMD at regular intervals (e.g., every 1–2 years in those with osteopenia or osteoporosis).1 70 71 73 74 Consider other potential causes of osteoporosis (e.g., vitamin D deficiency, hyperthyroidism, hyperparathyroidism, hypercalciuria).70 71 73 74
Initiate appropriate therapy to prevent bone loss as clinically indicated.71 Base decision to initiate antiresorptive therapy (e.g., bisphosphonate, denosumab) on overall risk of fracture and rate of bone loss.70 71 72 73 74
Lifestyle changes (e.g., weight-bearing exercise, abstinence from smoking, moderation in alcohol consumption) and supplemental calcium and vitamin D recommended in all women receiving adjuvant anastrozole therapy.36 46 47 70 71 72 73 74
Fetal/Neonatal Morbidity and Mortality
May cause fetal harm; embryotoxic and fetotoxic in animals.1 Test for pregnancy prior to initiation of the drug.1 Advise females of reproductive potential to use effective contraceptive methods during therapy and for ≥3 weeks after discontinuance of the drug.1 If used during pregnancy or patient becomes pregnant, apprise of potential fetal hazard.1
May cause fetal harm.1 (See Fetal/Neonatal Morbidity and Mortality under Cautions.)
Not known whether anastrozole or its metabolites are distributed into human milk; effects on nursing infant and milk production also unknown.1 Discontinue nursing during therapy and for 2 weeks after drug discontinuance.1
Has been used in clinical studies of adolescent boys 11–18 years of age with pubertal gynecomastia† and in girls 2 to <10 years of age with McCune-Albright syndrome and progressive precocious puberty†; however, efficacy not established for these indications.1
For adjuvant treatment of hormone receptor-positive early-stage breast cancer, efficacy (e.g., disease-free survival benefit) in women ≥65 years of age was less than efficacy observed in postmenopausal women <65 years of age.1
No substantial differences in efficacy for patients ≥65 years of age relative to younger adults when used as second line therapy for advanced breast cancer;1 moderately greater efficacy observed for patients ≥65 years of age when used as first-line therapy for locally advanced or metastatic breast cancer.1
Not studied in patients with severe hepatic impairment.1
Common Adverse Effects
Initial adjuvant therapy: Vasodilation, hot flushes (flashes), fatigue/asthenia, mood disturbance, pain, arthritis, arthralgia.1
Advanced-stage disease: GI disturbance (e.g., nausea), hot flushes, vasodilation, nausea, asthenia.1
Interactions for Anastrozole
Inhibits CYP1A2, 2C8/9, and 3A4 in vitro, but only at relatively high concentrations.1 Does not inhibit CYP2A6 or CYP2D6 in vitro.1 Pharmacokinetic interaction unlikely with drugs metabolized by CYP isoenzymes at recommended dosages.1
Pharmacokinetic interaction unlikely1
Antagonistic pharmacologic effects1
Concomitant use not recommended1
No clinically important effects on anticoagulant activity or pharmacokinetics of warfarin1
Rapidly and well absorbed after oral administration, with peak plasma concentrations usually attained within 2 hours under fasting conditions.1
Steady-state plasma concentrations achieved in about 7 days.1
Suppression of serum estradiol concentrations maintained for up to 6 days after discontinuance of daily anastrozole administration.1
Food reduces rate but does not affect extent of absorption.1
Not known whether anastrozole is distributed into milk.1
Plasma Protein Binding
Undergoes N-dealkylation, hydroxylation, and glucuronidation in the liver to multiple, pharmacologically inactive, metabolites.1
Hepatic metabolism (85%) and renal excretion (10%).1
Approximately 50 hours.1
No evidence of altered pharmacokinetics observed in women >80 years of age compared with women <50 years of age.1
Individuals with severe renal impairment (Clcr <30 mL/minute): Renal clearance decreased by approximately 50%, but total body clearance decreased by only 10%.1
Individuals with stable hepatic cirrhosis (related to alcohol abuse): Clearance reduced by approximately 30% compared with those with normal hepatic function;1 however, plasma concentrations within range compared with individuals with normal hepatic function.1
Advice to Patients
Importance of providing patient with a copy of the manufacturer’s patient information.1
Risk of osteoporosis.1 Lifestyle changes (e.g., weight-bearing exercise, abstinence from smoking, moderation of alcohol consumption) and dietary supplementation with calcium and vitamin D advised.36 46 47 Importance of BMD monitoring.1 71 73 74
Risk of fetal harm if used during pregnancy.1 Necessity of advising females of reproductive potential to use effective contraception during anastrozole therapy and for ≥3 weeks after the last dose.1 Importance of women informing clinicians immediately if they become pregnant or pregnancy is suspected during therapy.1 If pregnancy occurs, advise pregnant women of potential risk to the fetus.1
Importance of advising women to avoid breast-feeding while receiving anastrozole and for 2 weeks following discontinuance of therapy.1
Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription (e.g., estrogens, raloxifene, tamoxifen), and OTC drugs, as well as any concomitant illnesses.1
Increased risk of ischemic cardiovascular events in patients with preexisting ischemic heart disease.1
Importance of immediately informing clinician if manifestations of a serious allergic reaction (e.g., swelling of face, lips, tongue, and/or throat; difficulty in swallowing and/or breathing) occur.1
Importance of informing patients of other important precautionary information.1 (See Cautions.)
Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.
Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.
* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name
Anastrozole Film-coated Tablets
AHFS DI Essentials™. © Copyright 2021, Selected Revisions January 11, 2021. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.
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74. Hadji P, Aapro MS, Body JJ et al. Management of Aromatase Inhibitor-Associated Bone Loss (AIBL) in postmenopausal women with hormone sensitive breast cancer: Joint position statement of the IOF, CABS, ECTS, IEG, ESCEO IMS, and SIOG. J Bone Oncol. 2017; 7:1-12. http://www.ncbi.nlm.nih.gov/pubmed/28413771?dopt=AbstractPlus
10010. Francis PA, Regan MM, Fleming GF et al. Adjuvant ovarian suppression in premenopausal breast cancer. N Engl J Med. 2015; 372:436-46. http://www.ncbi.nlm.nih.gov/pubmed/25495490?dopt=AbstractPlus
10011. Pagani O, Regan MM, Walley BA et al. Adjuvant exemestane with ovarian suppression in premenopausal breast cancer. N Engl J Med. 2014; 371:107-18. http://www.ncbi.nlm.nih.gov/pubmed/24881463?dopt=AbstractPlus
10012. Francis PA, Pagani O, Fleming GF et al. Tailoring Adjuvant Endocrine Therapy for Premenopausal Breast Cancer. N Engl J Med. 2018; 379:122-137. http://www.ncbi.nlm.nih.gov/pubmed/29863451?dopt=AbstractPlus
10013. Tevaarwerk AJ, Wang M, Zhao F et al. Phase III comparison of tamoxifen versus tamoxifen plus ovarian function suppression in premenopausal women with node-negative, hormone receptor-positive breast cancer (E-3193, INT-0142): a trial of the Eastern Cooperative Oncology Group. J Clin Oncol. 2014; 32:3948-58. http://www.ncbi.nlm.nih.gov/pubmed/25349302?dopt=AbstractPlus
10016. Pan K, Bosserman LD, Chlebowski RT. Ovarian Suppression in Adjuvant Endocrine Therapy for Premenopausal Breast Cancer. J Clin Oncol. 2019; 37:858-861. http://www.ncbi.nlm.nih.gov/pubmed/30742565?dopt=AbstractPlus
10017. Burstein HJ, Lacchetti C, Anderson H et al. Adjuvant Endocrine Therapy for Women With Hormone Receptor-Positive Breast Cancer: American Society of Clinical Oncology Clinical Practice Guideline Update on Ovarian Suppression. J Clin Oncol. 2016; 34:1689-701. http://www.ncbi.nlm.nih.gov/pubmed/26884586?dopt=AbstractPlus
10018. Burstein HJ, Lacchetti C, Anderson H et al. Adjuvant Endocrine Therapy for Women With Hormone Receptor-Positive Breast Cancer: ASCO Clinical Practice Guideline Focused Update. J Clin Oncol. 2019; 37:423-438. http://www.ncbi.nlm.nih.gov/pubmed/30452337?dopt=AbstractPlus
10020. Dowsett M, Lønning PE, Davidson NE. Incomplete Estrogen Suppression With Gonadotropin-Releasing Hormone Agonists May Reduce Clinical Efficacy in Premenopausal Women With Early Breast Cancer. J Clin Oncol. 2016; 34:1580-3. http://www.ncbi.nlm.nih.gov/pubmed/26729430?dopt=AbstractPlus
10023. Gnant M, Mlineritsch B, Stoeger H et al. Adjuvant endocrine therapy plus zoledronic acid in premenopausal women with early-stage breast cancer: 62-month follow-up from the ABCSG-12 randomised trial. Lancet Oncol. 2011; 12:631-41. http://www.ncbi.nlm.nih.gov/pubmed/21641868?dopt=AbstractPlus
10024. Gnant M, Mlineritsch B, Stoeger H et al. Zoledronic acid combined with adjuvant endocrine therapy of tamoxifen versus anastrozol plus ovarian function suppression in premenopausal early breast cancer: final analysis of the Austrian Breast and Colorectal Cancer Study Group Trial 12. Ann Oncol. 2015; 26:313-20. http://www.ncbi.nlm.nih.gov/pubmed/25403582?dopt=AbstractPlus
10025. Bellet M, Gray KP, Francis PA et al. Twelve-Month Estrogen Levels in Premenopausal Women With Hormone Receptor-Positive Breast Cancer Receiving Adjuvant Triptorelin Plus Exemestane or Tamoxifen in the Suppression of Ovarian Function Trial (SOFT): The SOFT-EST Substudy. J Clin Oncol. 2016; 34:1584-93. http://www.ncbi.nlm.nih.gov/pubmed/26729437?dopt=AbstractPlus
10026. Perrone F, De Laurentiis M, De Placido S et al. Adjuvant zoledronic acid and letrozole plus ovarian function suppression in premenopausal breast cancer: HOBOE phase 3 randomised trial. Eur J Cancer. 2019; 118:178-186. http://www.ncbi.nlm.nih.gov/pubmed/31164265?dopt=AbstractPlus
10027. Chlebowski RT, Pan K, Col NF. Ovarian suppression in combination endocrine adjuvant therapy in premenopausal women with early breast cancer. Breast Cancer Res Treat. 2017; 161:185-190. http://www.ncbi.nlm.nih.gov/pubmed/27785653?dopt=AbstractPlus
10028. AHFS final determination of medical acceptance: Off-label use of endocrine therapy in combination with ovarian suppression for the adjuvant treatment of early-stage hormone receptor-positive breast cancer in premenopausal women. Published January 4, 2021.
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