Arimidex [Anastrozole] marketed by AstraZeneca Pharmaceuticals LP is a drug indicated in the treatment of adjuvant treatment [treatment following
surgery with or without radiation] of postmenopausal women with hormone receptor-positive early breast cancer.
It decreases the amount of estrogen in the body.
It is chemically described as 1, 3-Benzenediacetonitrile, a, a, a', a'-
Tetramethyl-5-(1H-1, 2, 4-triazol-1-ylmethyl).
Estrogen receptor positive breast cancer:
The estrogen receptor (ER) is a member of the nuclear hormone family of intracellular receptors which is activated by the hormone 17β-estradiol (estrogen).
The main function of the estrogen receptor is to act as a DNA binding transcription factor which would regulate gene expression. Apart from this function,
the estrogen receptor also has additional functions independent of DNA binding.
There are two types of estrogen receptors, α and β, both encoded by different genome [ESR1 on the sixth chromosome and ESR2 on the fourteenth chromosome
respectively]
In 70% cases of breast cancer, over expression of the estrogen receptor has been found, termed as ER positive.
Researches postulate two theses for the occurrence of the same:
- Binding of estrogen to the ER stimulates proliferation of mammary cells, this result in increase in cell division and DNA replication leading to
mutations.
- It is thought that estrogen metabolism could lead to production of genotoxic wastes.
Both these processes could result in the disruption of cell cycle, apoptosis and DNA repair and therefore tumor formation. ERα is certainly associated with
more differentiated tumors, while evidence that ERβ is involved is controversial. Different versions of the ESR1 gene have been identified (with
single-nucleotide polymorphisms) and are associated with different risks of developing breast cancer.
Particularly in postmenopausal women, the principal source of circulating estrogen (primarily Estradiol) is conversion of adrenally-generated androstenedione
to estrone by aromatase in peripheral tissues, with further conversion of estrone to estradiol. Many breast cancers also contain aromatase; the importance of
tumor-generated estrogens is uncertain.
Arimidex [Anastrozole] is approved for the initial treatment of postmenopausal women with hormone receptor-positive or hormone receptor-unknown locally
advanced or metastatic breast cancer and for the treatment of postmenopausal women with advanced breast cancer that has progressed following treatment with
tamoxifen. Patients with hormone receptor-negative disease and patients who did not previously respond to tamoxifen therapy rarely responded to Arimidex
[Anastrozole]
Anastrozole belongs to the class of aromatase inhibitors, where it inhibits the enzyme aromatase which is responsible for the conversion of androgens to
estrogen, meaning it selectively lowers the serum estradiol levels and at the same time doesn’t have any effect on the formation of adrenal corticosteroids
or aldosterone.
Basically it is a selective non steroidal aromatase inhibitor.
Orally administered Arimidex [anastrozole] is well absorbed into the systemic circulation. Its absorption is not affected by food.
With a half life of around 50 hours in post-menopausal females, it is excreted mainly via hepatic metabolism and by a lesser extent by renal metabolism
Indications and Usage:
Indications:
Adjuvant treatment of postmenopausal women with hormone receptor positive early breast cancer.
Arimidex [Anastrozole] is indicated for the first-line treatment of postmenopausal women with hormone receptor positive or hormone receptor unknown locally
advanced or metastatic breast cancer.
Arimidex [Anastrozole] is indicated for the treatment of advanced breast cancer in postmenopausal women with disease progression following tamoxifen therapy.
Patients with ER-negative disease and patients, who did not respond to previous tamoxifen therapy, rarely responded to Arimidex [Anastrozole].
Apart from these uses it has also been used as an off label drug in the treatment of growth disorder affected children to stop or slow the onset of puberty.
In males, Arimidex has proven effective in the off-label use of reducing estrogens (in particular and more importantly, estradiol). Hence can be used in
selective cases of benign prostatic hyperplasia, gynecomastia, and symptoms of hypogonadism
Usage:
- One tablet [1mg] to be taken once daily
- If the dose is missed, it is to be taken one as soon as possible provided that more than 12 hours are left before the next dose is due
- In case the dose is missed and if less than 12 hours are left before the next dose is due then do not take the missed dose.
Contraindication:
Contraindicated for any patient who is hypersensitive to Arimidex [Anastrozole] or to any of the excipients.
Warning:
- Pregnancy: PREGNANCY CATEGORY D
Arimidex [Anastrozole] can cause fetal damage if administered to pregnant women since it can cross the placenta. There is increased incidence of delayed
fetal development like incomplete ossification or decreased fetal weight.
In case Arimidex is administered to a pregnant woman or if a women receiving Arimidex becomes pregnant then she should be apprised of the potential hazards
associated with Arimidex during pregnancy.
- Nursing Mothers/ Lactating Mothers:
There is no evidence of Arimidex being secreted in breast milk. There are no proper studies to substantiate the risks, if any, associated with the use of
Arimidex, hence it should be avoided in lactating mothers.
- Pediatric use:
The safety and efficacy of Arimidex in pediatric patients have not been established.
- Estrogen containing therapies should not be used with Arimidex as they may diminish its pharmacological action.
- Tamoxifen should not be co-administered with Arimidex [anastrozole]
Side effects:
- Hot flushes – most common side effect
- Vaginal dryness
- Vaginal bleeding
- Hair thinning
- Anorexia
- Diarrhea
- Headache
- Rash
- Asthenia
- Dizziness
- Joint pain- use an analgesic to tide over the pain
- Nausea and vomiting
- Weakness
- Fatigue
- Brittle bones [osteoporosis] – advice vitamin D and calcium supplements. Proper diet. Perform bone mineral density (BMD) test regularly. Advice about
quitting smoking and alcohol
- Lymphedema: advice regarding avoiding using the affected arm for strenuous work.
Hepatic Impairment:
It is prudent to monitor the liver function tests in the presence of hepatic failure since Arimidex is majorly metabolized in the liver.
Renal Impairment:
No dose adjustments are required for patients with renal impairment.
Geriatric Usage:
No dose adjustments are required in geriatric age group.
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