Anastrozole Explained

Anastrozole, sold under the brand name Arimidex among others, is an antiestrogenic medication used in addition to other treatments for breast cancer.[1] Specifically it is used for hormone receptor-positive breast cancer. It has also been used to prevent breast cancer in those at high risk. It is taken by mouth.[2]

Common side effects of anastrozole include hot flashes, altered mood, joint pain, and nausea.[2] [1] Severe side effects include an increased risk of heart disease and osteoporosis.[2] Use during pregnancy may harm the baby.[2] Anastrozole is in the aromatase-inhibiting family of medications.[2] It works by blocking the production of estrogens in the body, and hence has antiestrogenic effects.[2]

Anastrozole was patented in 1987 and was approved for medical use in 1995.[3] [4] It is on the World Health Organization's List of Essential Medicines.[5] Anastrozole is available as a generic medication.[2] In 2021, it was the 182nd most commonly prescribed medication in the United States, with more than 2million prescriptions.[6] [7]

Medical uses

Breast cancer

Anastrozole is used in the treatment and prevention of breast cancer in women. The Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial was of localized breast cancer and women received either anastrozole, the selective estrogen receptor modulator tamoxifen, or both for five years, followed by five years of follow-up.[8] After more than 5 years the group that received anastrozole had better results than the tamoxifen group.[8] The trial suggested that anastrozole is the preferred medical therapy for postmenopausal women with localized estrogen receptor-positive breast cancer.[8]

Early puberty

Anastrozole is used at a dosage of 0.5 to 1 mg/day in combination with the antiandrogen bicalutamide in the treatment of peripheral precocious puberty, for instance due to familial male-limited precocious puberty (testotoxicosis) and McCune–Albright syndrome, in boys.[9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

Available forms

Anastrozole is available in the form of 1 mg oral tablets.[19] No alternative forms or routes are available.

Contraindications

Contraindications of anastrozole include hypersensitivity to anastrozole or any other component of anastrozole formulations, pregnancy, and breastfeeding. Hypersensitivity reactions to anastrozole including anaphylaxis, angioedema, and urticaria have been observed.

Side effects

Common side effects of anastrozole (≥10% incidence) include hot flashes,asthenia, arthritis, pain, arthralgia, hypertension, depression, nausea and vomiting, rash, osteoporosis, bone fractures, back pain, insomnia, headache, bone pain, peripheral edema, coughing, dyspnea, pharyngitis, and lymphedema. Serious but rare adverse effects (<0.1% incidence) 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 swallowing or breathing; and abnormal liver function tests as well as hepatitis.

Interactions

Anastrozole is thought to have clinically negligible inhibitory effects on the cytochrome P450 enzymes CYP1A2, CYP2A6, CYP2D6, CYP2C8, CYP2C9, and CYP2C19. As a result, it is thought that drug interactions of anastrozole with cytochrome P450 substrates are unlikely. No clinically significant drug interactions have been reported with anastrozole as of 2003.

Anastrozole does not affect circulating levels of tamoxifen or its major metabolite N-desmethyltamoxifen. However, tamoxifen has been found to decrease steady-state area-under-the-curve levels of anastrozole by 27%. But estradiol levels were not significantly different in the group that received both anastrozole and tamoxifen compared to the anastrozole alone group, so the decrease in anastrozole levels is not thought to be clinically important.

Pharmacology

Pharmacodynamics

Anastrozole works by reversibly binding to the aromatase enzyme, and through competitive inhibition blocks the conversion of androgens to estrogens in peripheral (extragonadal) tissues.[20] The medication has been found to achieve 96.7% to 97.3% inhibition of aromatase at a dosage of 1 mg/day and 98.1% inhibition of aromatase at a dosage of 10 mg/day in humans.[21] [22] As such, 1 mg/day is considered to be the minimal dosage required to achieve maximal suppression of aromatase with anastrozole. This decrease in aromatase activity results in an at least 85% decrease in estradiol levels in postmenopausal women. Levels of corticosteroids and other adrenal steroids are unaffected by anastrozole.

Pharmacokinetics

The bioavailability of anastrozole in humans is unknown, but it was found to be well-absorbed in animals. Absorption of anastrozole is linear over a dosage range of 1 to 20 mg/day in humans and does not change with repeated administration. Food does not significantly influence the extent of absorption of anastrozole. Peak levels of anastrozole occur a median 3 hours after administration, but with a wide range of 2 to 12 hours. Steady-state levels of anastrozole are achieved within 7 to 10 days of continuous administration, with 3.5-fold accumulation. However, maximal suppression of estradiol levels occurs within 3 or 4 days of therapy.

Active efflux of anastrozole by P-glycoprotein at the blood–brain barrier has been found to limit the central nervous system penetration of anastrozole in rodents, whereas this was not the case with letrozole and vorozole.[23] [24] [25] As such, anastrozole may have peripheral selectivity in humans, although this has yet to be confirmed. In any case, estradiol is synthesized peripherally and readily crosses the blood–brain barrier, so anastrozole would still expected to reduce estradiol levels in the central nervous system to a certain degree. The plasma protein binding of anastrozole is 40%.

The metabolism of anastrozole is by N-dealkylation, hydroxylation, and glucuronidation. Inhibition of aromatase is due to anastrozole itself rather than to metabolites, with the major circulating metabolite being inactive. The elimination half-life of anastrozole is 40 to 50 hours (1.7 to 2.1 days). This allows for convenient once-daily administration. The medication is eliminated predominantly by metabolism in the liver (83 to 85%) but also by residual excretion by the kidneys unchanged (11%). Anastrozole is excreted primarily in urine but also to a lesser extent in feces.

Chemistry

Anastrozole is a nonsteroidal benzyl triazole.[26] It is also known as α,α,α',α'-tetramethyl-5-(1H-1,2,4-triazol-1-ylmethyl)-m-benzenediacetonitrile. Anastrozole is structurally related to letrozole, fadrozole, and vorozole, with all being classified as azoles.[27] [28] [29] [30]

History

Anastrozole was patented by Imperial Chemical Industries (ICI) in 1987 and was approved for medical use, specifically the treatment of breast cancer, in 1995.

Society and culture

Generic names

Anastrozole is the generic name of the drug and its,,, and .

Brand names

Anastrozole is primarily sold under the brand name Arimidex.[31] However, it is also marketed under a variety of other brand names throughout the world.

Availability

Anastrozole is available widely throughout the world.

Research

Anastrozole is surprisingly ineffective at treating gynecomastia, in contrast to selective estrogen receptor modulators like tamoxifen.[32] [33]

Anastrozole was under development for the treatment of female infertility but did not complete development and hence was never approved for this indication.[34]

An anastrozole and levonorgestrel vaginal ring (developmental code name BAY 98–7196) was under development for use as a hormonal contraceptive and treatment for endometriosis, but development was discontinued in November 2018 and the formulation was never marketed.[35]

Anastrozole increases testosterone levels in males and has been studied as an alternative method of androgen replacement therapy in men with hypogonadism.[36] [37] However, there are concerns about its long-term influence on bone mineral density in this patient population, as well as other adverse effects.

Notes and References

  1. Web site: Highlights of Prescribing Information Anastrozole . FDA . 31 July 2019.
  2. Web site: Anastrozole. The American Society of Health-System Pharmacists. 8 December 2016. live. https://web.archive.org/web/20161221013418/https://www.drugs.com/monograph/anastrozole.html. 21 December 2016.
  3. Book: Fischer J, Ganellin CR . Analogue-based Drug Discovery. 2006. John Wiley & Sons. 9783527607495. 516. en. live. https://web.archive.org/web/20161220163842/https://books.google.ca/books?id=FjKfqkaKkAAC&pg=PA516. 20 December 2016.
  4. Dukes M . The relevance of preclinical models to the treatment of postmenopausal breast cancer . Oncology . 54 . 2 . 6–10 . 1997 . 9394853 . 10.1159/000227748 .
  5. Book: ((World Health Organization)) . World Health Organization model list of essential medicines: 21st list 2019 . 2019 . 10665/325771 . World Health Organization . World Health Organization . Geneva . WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO . free .
  6. Web site: The Top 300 of 2021 . ClinCalc . 14 January 2024 . 15 January 2024 . https://web.archive.org/web/20240115223848/https://clincalc.com/DrugStats/Top300Drugs.aspx . live .
  7. Web site: Anastrozole - Drug Usage Statistics . ClinCalc . 14 January 2024.
  8. Howell A, Cuzick J, Baum M, Buzdar A, Dowsett M, Forbes JF, Hoctin-Boes G, Houghton J, Locker GY, Tobias JS . Results of the ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial after completion of 5 years' adjuvant treatment for breast cancer . Lancet . 365 . 9453 . 60–62 . 2005 . 15639680 . 10.1016/S0140-6736(04)17666-6 . 8350282 . Michael Baum (surgeon) .
  9. Web site: Casodex® (bicalutamide) Tablets . FDA . live . https://web.archive.org/web/20190730062812/https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/020498s028lbl.pdf . 30 July 2019 .
  10. Book: Schoelwer M, Eugster EA . Puberty from Bench to Clinic . Treatment of Peripheral Precocious Puberty . 29 . 230–9 . 2015 . 26680582 . 5345994 . 10.1159/000438895 . 978-3-318-02788-4 . Endocrine Development .
  11. Book: Zacharin M . Disorders of Puberty: Pharmacotherapeutic Strategies for Management. Pediatric Pharmacotherapy. Handbook of Experimental Pharmacology . 261 . 507–538 . May 2019 . Springer. 31144045 . 10.1007/164_2019_208 . 978-3-030-50493-9 . 169040406 .
  12. Book: Kliegman RM, Stanton B, St Geme J, Schor NF . Nelson Textbook of Pediatrics . 17 April 2015 . Elsevier Health Sciences . 978-0-323-26352-8 . 2661–.
  13. Neyman A, Eugster EA . Treatment of Girls and Boys with McCune-Albright Syndrome with Precocious Puberty - Update 2017 . Pediatric Endocrinology Reviews . 15 . 2 . 136–141 . December 2017 . 29292624 . 5808444 . 10.17458/per.vol15.2017.nau.treatmentgirlsboys .
  14. Book: Haddad NG, Eugster EA . Handbook of Growth and Growth Monitoring in Health and Disease . Peripheral Precocious Puberty: Interventions to Improve Growth. 2012. 1199–1212. Springer . 10.1007/978-1-4419-1795-9_71. 978-1-4419-1794-2.
  15. Haddad NG, Eugster EA . Peripheral precocious puberty including congenital adrenal hyperplasia: causes, consequences, management and outcomes . Best Practice & Research. Clinical Endocrinology & Metabolism . 33 . 3 . 101273 . June 2019 . 31027974 . 10.1016/j.beem.2019.04.007 . free . 135410503 . 1805/19111 .
  16. Book: Misra M, Radovick S . Pediatric Endocrinology . Precocious Puberty. 2018. 589–615. Springer . 10.1007/978-3-319-73782-9_26. 978-3-319-73781-2.
  17. Mauras N . Strategies for maximizing growth in puberty in children with short stature . Pediatric Clinics of North America . 58 . 5 . 1167–79, x . October 2011 . 21981954 . 10.1016/j.pcl.2011.07.007 .
  18. Fuqua JS . Treatment and outcomes of precocious puberty: an update . The Journal of Clinical Endocrinology and Metabolism . 98 . 6 . 2198–2207 . June 2013 . 23515450 . 10.1210/jc.2013-1024 . free .
  19. Book: White R, Bradnam V . Handbook of Drug Administration via Enteral Feeding Tubes, 3rd edition. 11 March 2015. Pharmaceutical Press. 978-0-85711-162-3. 108–.
  20. Simpson ER . Sources of estrogen and their importance . The Journal of Steroid Biochemistry and Molecular Biology . 86 . 3–5 . 225–230 . September 2003 . 14623515 . 10.1016/S0960-0760(03)00360-1 . 11210435 .
  21. Lønning P, Pfister C, Martoni A, Zamagni C . Pharmacokinetics of third-generation aromatase inhibitors . Seminars in Oncology . 30 . 4 Suppl 14 . 23–32 . August 2003 . 14513434 . 10.1016/S0093-7754(03)00305-1 .
  22. Lønning P . Clinical pharmacokinetics of aromatase inhibitors and inactivators . Clinical Pharmacokinetics . 42 . 7 . 619–631 . 2003 . 12844324 . 10.2165/00003088-200342070-00002 . 9585901 .
  23. Costa R, Carneiro BA, Wainwright DA, Santa-Maria CA, Kumthekar P, Chae YK, Gradishar WJ, Cristofanilli M, Giles FJ . Developmental therapeutics for patients with breast cancer and central nervous system metastasis: current landscape and future perspectives . Annals of Oncology . 28 . 1 . 44–56 . January 2017 . 28177431 . 7360139 . 10.1093/annonc/mdw532 . free .
  24. Russell N, Cheung A, Grossmann M . Estradiol for the mitigation of adverse effects of androgen deprivation therapy . Endocrine-Related Cancer . 24 . 8 . R297–R313 . August 2017 . 28667081 . 10.1530/ERC-17-0153 . free .
  25. Miyajima M, Kusuhara H, Takahashi K, Takashima T, Hosoya T, Watanabe Y, Sugiyama Y . Investigation of the effect of active efflux at the blood-brain barrier on the distribution of nonsteroidal aromatase inhibitors in the central nervous system . Journal of Pharmaceutical Sciences . 102 . 9 . 3309–3319 . September 2013 . 23712697 . 10.1002/jps.23600 . free .
  26. Sanford M, Plosker GL . Anastrozole: a review of its use in postmenopausal women with early-stage breast cancer . Drugs . 68 . 9 . 1319–1340 . 2008 . 18547136 . 10.2165/00003495-200868090-00007 . 195687223 .
  27. Book: Thurston DE . Chemistry and Pharmacology of Anticancer Drugs. 22 November 2006. CRC Press. 978-1-4200-0890-6. 136–.
  28. Book: Roy, Kunal. Quantitative Structure-Activity Relationships in Drug Design, Predictive Toxicology, and Risk Assessment. 28 February 2015. IGI Global. 978-1-4666-8137-8. 437–.
  29. Book: Smith DA, Allerton C, Kalgutkar AS, van de Waterbeemd H, Walker DK . Pharmacokinetics and Metabolism in Drug Design. 13 September 2012. John Wiley & Sons. 978-3-527-64529-9. 197–.
  30. Book: Environmental Health Perspectives: Supplements. 1993. U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, National Institute of Environmental Health Sciences. 256–260.
  31. Web site: Anastrozole.
  32. Fagerlund A, Cormio L, Palangi L, Lewin R, Santanelli di Pompeo F, Elander A, Selvaggi G . Gynecomastia in Patients with Prostate Cancer: A Systematic Review . PLOS ONE . 10 . 8 . e0136094 . 2015 . 26308532 . 4550398 . 10.1371/journal.pone.0136094 . free . 2015PLoSO..1036094F .
  33. Bedognetti D, Rubagotti A, Zoppoli G, Boccardo F . Gynaecomastia: the anastrozole paradox . Journal of Pediatric Endocrinology & Metabolism . 23 . 1–2 . 205–206 . 2010 . 20432826 . 10.1515/JPEM.2010.23.1-2.205 . 41999854 .
  34. Web site: Anastrozole - AstraZeneca . Adis Insight .
  35. Web site: Anastrozole/levonorgestrel intravaginal ring - Bayer HealthCare . Adis Insight .
  36. Book: Serefoglu EC, Gokce A, Hellstrom WJ, Guay AT . Alternate Therapies for Testosterone Replacement . Androgen Deficiency and Testosterone Replacement . Current Clinical Urology . 2013. 141–147. Humana Press . 10.1007/978-1-62703-179-0_11. 978-1-62703-178-3.
  37. Khera M, Adaikan G, Buvat J, Carrier S, El-Meliegy A, Hatzimouratidis K, McCullough A, Morgentaler A, Torres LO, Salonia A . Diagnosis and Treatment of Testosterone Deficiency: Recommendations From the Fourth International Consultation for Sexual Medicine (ICSM 2015) . The Journal of Sexual Medicine . 13 . 12 . 1787–1804 . December 2016 . 27914560 . 10.1016/j.jsxm.2016.10.009 .

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