What is Arimidex (anastrozole)?

Arimidex (anastrozole) is a type of anti-cancer medication called an aromatase inhibitor, used for the adjuvant or initial treatment of breast cancer in post-menopausal women. 

Estrogen causes or increases growth of certain breast cancers. Arimidex works by blocking aromatase enzyme, which is involved in estrogen production in the body, which leads to decreased tumor size or delayed progression of tumor growth in some women. 

Common side effects of Arimidex include:

Serious side effects of Arimidex include:

  • skin reactions such as lesions, ulcers, or blisters;
  • allergic reactions with swelling of the face, lips, tongue, and/or throat that may cause difficulty in swallowing and/or breathing; and
  • changes in liver function tests, including inflammation of the liver (symptoms may include malaise, jaundice, liver pain, or liver swelling).

Drug interactions of Arimidex include tamoxifen because tamoxifen can reduce Arimidex levels in the body and decrease its therapeutic effects. 

Estrogens decrease the effect of Arimidex by increasing estrogen levels in the body. 

Arimidex is not recommended for pregnant mothers under any circumstances. Arimidex may cause fetal harm and terminate pregnancy

It is unknown if Arimidex enters breast milk. Arimidex should not be administered to breastfeeding mothers to avoid any harm to the newborn.

What are the important side effects of Arimidex (anastrozole)?

Side effects of anastrozole are:

Arimidex (anastrozole) side effects list for healthcare professionals

Serious adverse reactions with Arimidex occurring in less than 1 in 10,000 patients, are:

  • 1) skin reactions such as lesions, ulcers, or blisters;
  • 2) allergic reactions with swelling of the face, lips, tongue, and/or throat. This may cause difficulty in swallowing and/or breathing; and
  • 3) changes in blood tests of the liver function, including inflammation of the liver with symptoms that may include a general feeling of not being well, with or without jaundice, liver pain or liver swelling.

Common adverse reactions (occurring with an incidence of ≥ 10%) in women taking Arimidex included:

In the ATAC trial, the most common reported adverse reaction ( > 0.1%) leading to discontinuation of therapy for both treatment groups was hot flashes, although there were fewer patients who discontinued therapy as a result of hot flashes in the Arimidex group.

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Clinical Trials Experience

Adjuvant Therapy

Adverse reaction data for adjuvant therapy are based on the ATAC trial. The median duration of adjuvant treatment for safety evaluation was 59.8 months and 59.6 months for patients receiving Arimidex 1 mg and tamoxifen 20 mg, respectively.

Adverse reactions occurring with an incidence of at least 5% in either treatment group during treatment or within 14 days of the end of treatment are presented in Table 1.

Table 1 :Adverse reactions occurring with an incidence of at least 5% in either treatment group during treatment, or within 14 days of the end of treatment in the ATAC trial*

Body system and adverse reactions by COSTART preferred term*Arimidex 1 mg
(N§ = 3092)
Tamoxifen 20 mg
(N§ = 3094)
Body as a whole
Asthenia575 (19)544 (18)
Pain533(17)485 (16)
Back pain321 (10)309 (10)
Headache314 (10)249 (8)
Abdominal pain271 (9)276 (9)
Infection285 (9)276 (9)
Accidental injury311 (10)303 (10)
Flu syndrome175 (6)195 (6)
Chest pain200 (7)150 (5)
Neoplasm162 (5)144 (5)
Cyst138 (5)162 (5)
Cardiovascular
Vasodilatation1104 (36)1264 (41)
Hypertension402 (13)349 (11)
Digestive
Nausea343 (11)335 (11)
Constipation249 (8)252 (8)
Diarrhea265 (9)216 (7)
Dyspepsia206 (7)169 (6)
Gastrointestinal disorder210 (7)158 (5)
Hemic and lymphatic
Lymphedema304 (10)341 (11)
Anemia113 (4)159 (5)
Metabolic and nutritional
Peripheral edema311 (10)343 (11)
Weight gain285 (9)274 (9)
Hypercholesterolemia278 (9)108 (3.5)
Musculoskeletal
Arthritis512 (17)445 (14)
Arthralgia467 (15)344 (11)
Osteoporosis325 (11)226 (7)
Fracture315(10)209 (7)
Bone pain201 (7)185 (6)
Arthrosis207 (7)156 (5)
Joint Disorder184 (6)160 (5)
Myalgia179 (6)160 (5)
Nervous system
Depression413 (13)382 (12)
Insomnia309 (10)281 (9)
Dizziness236 (8)234 (8)
Anxiety195 (6)180 (6)
Paresthesia215 (7)145 (5)
Respiratory
Pharyngitis443 (14)422 (14)
Cough increased261 (8)287 (9)
Dyspnea234 (8)237 (8)
Sinusitis184 (6)159 (5)
Bronchitis167 (5)153 (5)
Skin and appendages
Rash333 (11)387 (13)
Sweating145 (5)177 (6)
Special Senses
Cataract Specified182 (6)213 (7)
Urogenital
Leukorrhea86 (3)286 (9)
Urinary tract infection244 (8)313(10)
Breast pain251 (8)169 (6)
Breast Neoplasm164 (5)139 (5)
Vulvovaginitis194 (6)150 (5)
Vaginal Hemorrhage¶122 (4)180 (6)
Vaginitis125 (4)158 (5)
* The combination arm was discontinued due to lack of efficacy benefit at 33 months of follow-up.
†COSTART Coding Symbols for Thesaurus of Adverse Reaction Terms.
‡ A patient may have had more than 1 adverse reaction, including more than 1 adverse reaction in the same body system.
§ N=Number of patients receiving the treatment.
¶Vaginal Hemorrhage without further diagnosis.

Certain adverse reactions and combinations of adverse reactions were prospectively specified for analysis, based on the known pharmacologic properties and side effect profiles of the two drugs (see Table 2).

Table 2 : Number of Patients with Pre-specified Adverse Reactions in ATAC Trial*

Arimidex
N=3092 (%)
Tamoxifen
N=3094 (%)
Odds-ratio95% CI
Hot Flashes1104 (36)1264 (41)0.800.73 -0.89
Musculoskeletal Events'11100 (36)911 (29)1.321.19 -1.47
Fatigue/Asthenia575 (19)544 (18)1.070.94 -1.22
Mood Disturbances597 (19)554 (18)1.100.97 - 1.25
Nausea and Vomiting393 (13)384 (12)1.030.88 -1.19
All Fractures315 (10)209 (7)1.571.30 -1.88
Fractures of Spine, Hip, or Wrist133 (4)91 (3)1.481.13 -1.95
  Wrist/Colles’ fractures67 (2)50 (2)
  Spine fractures43 (1)22 (1)
  Hip fractures28 (1)26 (1)
Cataracts182 (6)213 (7)0.850.69 -1.04
Vaginal Bleeding167 (5)317(10)0.500.41 -0.61
Ischemic Cardiovascular Disease127 (4)104 (3)1.230.95 -1.60
Vaginal Discharge109 (4)408 (13)0.240.19 -0.30
Venous Thromboembolic events87 (3)140 (5)0.610.47 -0.80
Deep Venous Thromboembolic Events48 (2)74 (2)0.640.45 -0.93
Ischemic Cerebrovascular Event62 (2)88 (3)0.700.50 -0.97
Endometrial Cancer*4 (0.2)13 (0.6)0.310.10 -0.94
* Patients with multiple events in the same category are counted only once in that category.
†Refers to joint symptoms, including joint disorder, arthritis, arthrosis and arthralgia.
‡ Percentages calculated based upon the numbers of patients with an intact uterus at baseline

Ischemic Cardiovascular Events

Between treatment arms in the overall population of 6186 patients, there was no statistical difference in ischemic cardiovascular events (4% Arimidex vs. 3% tamoxifen).

In the overall population, angina pectoris was reported in 71/3092 (2.3%) patients in the Arimidex arm and 51/3094 (1.6%) patients in the tamoxifen arm; myocardial infarction was reported in 37/3092 (1.2%) patients in the Arimidex arm and 34/3094 (1.1%) patients in the tamoxifen arm.

In women with pre-existing ischemic heart disease 465/6186 (7.5%), the incidence of ischemic cardiovascular events was 17% in patients on Arimidex and 10% in patients on tamoxifen. In this patient population, angina pectoris was reported in 25/216 (11.6%) patients receiving Arimidex and 13/249 (5.2%) patients receiving tamoxifen; myocardial infarction was reported in 2/216 (0.9%) patients receiving Arimidex and 8/249 (3.2%) patients receiving tamoxifen.

Bone Mineral Density Findings

Results from the ATAC trial bone substudy at 12 and 24 months demonstrated that patients receiving Arimidex had a mean decrease in both lumbar spine and total hip bone mineral density (BMD) compared to baseline. Patients receiving tamoxifen had a mean increase in both lumbar spine and total hip BMD compared to baseline.

Because Arimidex lowers circulating estrogen levels it may cause a reduction in bone mineral density.

A post-marketing trial assessed the combined effects of Arimidex and the bisphosphonate risedronate on changes from baseline in BMD and markers of bone resorption and formation in postmenopausal women with hormone receptor-positive early breast cancer. All patients received calcium and vitamin D supplementation. At 12 months, small reductions in lumbar spine bone mineral density were noted in patients not receiving bisphosphonates. Bisphosphonate treatment preserved bone density in most patients at risk of fracture.

Postmenopausal women with early breast cancer scheduled to be treated with Arimidex should have their bone status managed according to treatment guidelines already available for postmenopausal women at similar risk of fragility fracture.

Cholesterol

During the ATAC trial, more patients receiving Arimidex were reported to have an elevated serum cholesterol compared to patients receiving tamoxifen (9% versus 3.5%, respectively).

A post-marketing trial also evaluated any potential effects of Arimidex on lipid profile. In the primary analysis population for lipids (Arimidex alone), there was no clinically significant change in LDL-C from baseline to 12 months and HDL-C from baseline to 12 months.

In secondary population for lipids (Arimidex+risedronate), there also was no clinically significant change in LDL-C and HDL-C from baseline to 12 months.

In both populations for lipids, there was no clinically significant difference in total cholesterol (TC) or serum triglycerides (TG) at 12 months compared with baseline.

In this trial, treatment for 12 months with Arimidex alone had a neutral effect on lipid profile. Combination treatment with Arimidex and risedronate also had a neutral effect on lipid profile.

The trial provides evidence that postmenopausal women with early breast cancer scheduled to be treated with Arimidex should be managed using the current National Cholesterol Education Program guidelines for cardiovascular risk-based management of individual patients with LDL elevations.

Other Adverse Reactions

Patients receiving Arimidex had an increase in joint disorders (including arthritis, arthrosis and arthralgia) compared with patients receiving tamoxifen. Patients receiving Arimidex had an increase in the incidence of all fractures (specifically fractures of spine, hip and wrist) [315 (10%)] compared with patients receiving tamoxifen [209 (7%)].

Patients receiving Arimidex had a higher incidence of carpal tunnel syndrome [78 (2.5%)] compared with patients receiving tamoxifen [22 (0.7%)].

Vaginal bleeding occurred more frequently in the tamoxifen-treated patients versus the Arimidex-treated patients 317 (10%) versus 167 (5%), respectively.

Patients receiving Arimidex had a lower incidence of hot flashes, vaginal bleeding, vaginal discharge, endometrial cancer, venous thromboembolic events and ischemic cerebrovascular events compared with patients receiving tamoxifen.

10-Year Median Follow-Up Safety Results From The ATAC Trial

Results are consistent with the previous analyses.

Serious adverse reactions were similar between Arimidex (50%) and tamoxifen (51%).

  • Cardiovascular events were consistent with the known safety profiles of Arimidex and tamoxifen.
  • The cumulative incidences of all first fractures (both serious and non-serious, occurring either during or after treatment) was higher in the Arimidex group (15%) compared to the tamoxifen group (11%). This increased first fracture rate during treatment did not continue in the post-treatment follow-up period.
  • The cumulative incidence of new primary cancers was similar in the Arimidex group (13.7%) compared to the tamoxifen group (13.9%). Consistent with the previous analyses, endometrial cancer was higher in the tamoxifen group (0.8%) compared to the Arimidex group (0.2%).
  • The overall number of deaths (during or off-trial treatment) was similar between the treatment groups. There were more deaths related to breast cancer in the tamoxifen than in the Arimidex treatment group.
First-Line Therapy

Adverse reactions occurring with an incidence of at least 5% in either treatment group of trials 0030 and 0027 during or within 2 weeks of the end of treatment are shown in Table 3.

Table 3 : Adverse Reactions Occurring with an Incidence of at Least 5% in Trials 0030 and 0027

Body system
Adverse Reaction*
Number (%) of subjects
Arimidex (N=506)Tamoxifen (N=511)
Whole body
Asthenia83 (16)81(16)
Pain70(14)73 (14)
Back pain60(12)68 (13)
Headache47 (9)40 (8)
Abdominal pain40 (8)38 (7)
Chest pain37 (7)37 (7)
Flu syndrome35 (7)30 (6)
Pelvic pain23 (5)30 (6)
Cardiovascular
Vasodilation128 (25)106 (21)
Hypertension25 (5)36 (7)
Digestive
Nausea94 (19)106 (21)
Constipation47 (9)66 (13)
Diarrhea40 (8)33 (6)
Vomiting38 (8)36 (7)
Anorexia26 (5)46 (9)
Metabolic and Nutritional
Peripheral edema51 (10)41 (8)
Musculoskeletal
Bone pain54 (11)52 (10)
Nervous
Dizziness30 (6)22 (4)
Insomnia30 (6)38 (7)
Depression23 (5)32 (6)
Hypertonia16 (3)26 (5)
Respiratory
Cough increased55 (11)52 (10)
Dyspnea51 (10)47 (9)
Pharyngitis49 (10)68 (13)
Skin and appendages
Rash38 (8)34 (8)
Urogenital
Leukorrhea9 (2)31 (6)
* A patient may have had more than 1 adverse event.

Less frequent adverse experiences reported in patients receiving Arimidex l mg in either Trial 0030 or Trial 0027 were similar to those reported for second-line therapy.

Based on results from second-line therapy and the established safety profile of tamoxifen, the incidences of 9 pre-specified adverse event categories potentially causally related to one or both of the therapies because of their pharmacology were statistically analyzed. No significant differences were seen between treatment groups.

Table 4 : Number of Patients with Pre-specified Adverse Reactions in Trials 0030 and 0027

Adverse Reaction*Number (n) and Percentage of Patients
Arimidex 1 mg
(N=506)
n (%)
NOLVADEX 20 mg
(N=511)
n (%)
Depression23 (5)32 (6)
Tumor Flare15 (3)18 (4)
Thromboembolic Disease†18 (4)33 (6)
Venous†515
Coronary and Cerebral‡1319
Gastrointestinal Disturbance170 (34)196 (38)
Hot Flushes134 (26)118 (23)
Vaginal Dryness9 (2)3 (1)
Lethargy6 (1)15 (3)
Vaginal Bleeding5 (1)11 (2)
Weight Gain11 (2)8 (2)
* A patient may have had more than 1 adverse reaction.
†Includes pulmonary embolus, thrombophlebitis, retinal vein thrombosis.
‡ Includes myocardial infarction, myocardial ischemia, angina pectoris, cerebrovascular accident, cerebral ischemia and cerebral infarct.

Second-Line Therapy

Arimidex was tolerated in two controlled clinical trials (i.e., Trials 0004 and 0005), with less than 3.3% of the Arimidex-treated patients and 4.0% of the megestrol acetate-treated patients withdrawing due to an adverse reaction.

The principal adverse reaction more common with Arimidex than megestrol acetate was diarrhea. Adverse reactions reported in greater than 5% of the patients in any of the treatment groups in these two controlled clinical trials, regardless of causality, are presented below:

Table 5 :Number (N) and Percentage of Patients with Adverse Reactions in Trials 0004 and 0005

Adverse Reaction*Arimidex 1 mg
(N=262)
Arimidex 10 mg
(N=246)
Megestrol Acetate 160 mg
(N=253)
n%n%n%
Asthenia42(16)33(13)47(19)
Nausea41(16)48(20)28(11)
Headache34(13)44(18)24(9)
Hot Flashes32(12)29(11)21(8)
Pain28(11)38(15)29(11)
Back Pain28(11)26(11)19(8)
Dyspnea24(9)27(11)53(21)
Vomiting24(9)26(11)16(6)
Cough Increased22(8)18(7)19(8)
Diarrhea22(8)18(7)7(3)
Constipation18(7)18(7)21(8)
Abdominal Pain18(7)14(6)18(7)
Anorexia18(7)19(8)11(4)
Bone Pain17(6)26(12)19(8)
Pharyngitis16(6)23(9)15(6)
Dizziness16(6)12(5)15(6)
Rash15(6)15(6)19(8)
Dry Mouth15(6)11(4)13(5)
Peripheral Edema14(5)21(9)28(11)
Pelvic Pain14(5)17(7)13(5)
Depression14(5)6(2)5(2)
Chest Pain13(5)18(7)13(5)
Paresthesia12(5)15(6)9(4)
Vaginal Hemorrhage6(2)4(2)13(5)
Weight Gain4(2)9(4)30(12)
Sweating4(2)3(1)16(6)
Increased Appetite0(0)1(0)13(5)
* A patient may have had more than one adverse reaction. Other less frequent (2% to 5%) adverse reactions reported in patients receiving Arimidex l mg in either Trial 0004 or Trial 0005 are listed below. These adverse experiences are listed by body system and are in order of decreasing frequency within each body system regardless of assessed causality.

Body as a Whole: Flu syndrome; fever; neck pain; malaise; accidental injury; infection

Cardiovascular: Hypertension; thrombophlebitis

Hepatic: Gamma GT increased; SGOT increased; SGPT increased Hematologic: Anemia; leukopenia

Metabolic and Nutritional: Alkaline phosphatase increased; weight loss

Mean serum total cholesterol levels increased by 0.5 mmol/L among patients receiving Arimidex. Increases in LDL cholesterol have been shown to contribute to these changes.

Musculoskeletal: Myalgia; arthralgia; pathological fracture

Nervous: Somnolence; confusion; insomnia; anxiety; nervousness

Respiratory: Sinusitis; bronchitis; rhinitis

Skin and Appendages: Hair thinning (alopecia); pruritus

Urogenital: Urinary tract infection; breast pain

The incidences of the following adverse reaction groups potentially causally related to one or both of the therapies because of their pharmacology, were statistically analyzed:

These six groups, and the adverse reactions captured in the groups, were prospectively defined. The results are shown in the table below.

Table 6 : Number (n) and Percentage of Patients with Pre-specified Adverse Reactions in Trials 0004 and 0005

Adverse Reaction GroupArimidex1 mg
(N=262)
Arimidex10 mg
(N=246)
Megestrol Acetate160 mg
(N=253)
n(%)n(%)n(%)
Gastrointestinal Disturbance77(29)81(33)54(21)
Hot Flushes33(13)29(12)35(14)
Edema19(7)28(11)35(14)
Thromboembolic Disease9(3)4(2)12(5)
Vaginal Dryness5(2)3(1)2(1)
Weight Gain4(2)10(4)30(12)

Post-Marketing Experience

These adverse reactions are reported voluntarily from a population of uncertain size. Therefore, it is not always possible to estimate reliably their frequency or establish a causal relationship to drug exposure. The following have been reported in post-approval use of Arimidex:

What drugs interact with Arimidex (anastrozole)?

Tamoxifen

Co-administration of anastrozole and tamoxifen in breast cancer patients reduced anastrozole plasma concentration by 27%. However, the co-administration of anastrozole and tamoxifen did not affect the pharmacokinetics of tamoxifen or N-desmethyltamoxifen.

At a median follow-up of 33 months, the combination of Arimidex and tamoxifen did not demonstrate any efficacy benefit when compared with tamoxifen in all patients as well as in the hormone receptor-positive subpopulation. This treatment arm was discontinued from the trial. Based on clinical and pharmacokinetic results from the ATAC trial, tamoxifen should not be administered with anastrozole.

Estrogen

Estrogen-containing therapies should not be used with Arimidex as they may diminish its pharmacological action.

Warfarin

In a study conducted in 16 male volunteers, anastrozole did not alter the exposure (as measured by C max and AUC) and anticoagulant activity (as measured by prothrombin time, activated partial thromboplastin time, and thrombin time) of both R-and S-warfarin.

Cytochrome P450 Based on in vitro and in vivo results, it is unlikely that co-administration of Arimidex 1 mg will affect other drugs as a result of inhibition of cytochrome P450.

Summary

Arimidex (anastrozole) is a type of anti-cancer medication called an aromatase inhibitor, used for the adjuvant or initial treatment of breast cancer in post-menopausal women. Arimidex works by blocking aromatase enzyme, which is involved in estrogen production in the body, which leads to decreased tumor size or delayed progression of tumor growth in some women. Common side effects of Arimidex include hot flashes, pain, arthritis, headache, increased blood pressure, depression, nausea, vomiting, bone pain, weakened bones, sleeplessness, and rash. Arimidex is not recommended for pregnant mothers under any circumstances. Arimidex may cause fetal harm and terminate pregnancy. It is unknown if Arimidex enters breast milk. Arimidex should not be administered to breastfeeding mothers to avoid any harm to the newborn.

Treatment & Diagnosis

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Medically Reviewed on 5/21/2020
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