Can You Take Arimidex (Anastrozole) Every Other Day?

Arimidex is only indicated to be dosed once daily by the FDA.

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Nov 01, 2018

Sandra asked

Can Arimidex be taken every other day? And can I still consume cruciferous vegetables since those types of vegetables stabilize estrogen?

At a glance

  • Arimidex is only FDA approved for once-daily dosing.
  • Although there are reports of alternative dosing schedules (e.g. every other day) being effective, they have not been well-studied.
  • Do not change your dosing schedule of Arimidex without first speaking with your doctor.

Answer

Medication Timing

Arimidex (Anastrozole) is an aromatase inhibitor used for the treatment of breast cancer in post-menopausal women. It is also used off-label for the treatment of:

  • Endometriosis
  • Uterine leiomyomata
  • Testosterone induced gynecomastia in men
  • Prevention of breast cancer in post-menopausal women

Aromatase inhibitors are generally more effective in post-menopausal women since they work to decrease estrogen by inhibiting the endogenous conversion of androgens to estrogen.

They don't inhibit the production of estrogen in the ovaries, which is the primary source of estrogen in premenopausal women.

Aromatase inhibitors, like Arimidex, are most often dosed once-daily.

Arimidex Dosing

Arimidex is only indicated by the FDA to be dosed once daily and studies evaluating the effectiveness of the drug have not evaluated intermittent dosing schedules, such as with every other day dosing.

Most pharmacokinetic studies have also only evaluated dosing at once daily intervals. The prescribing information for Arimidex describes the following:

"Steady-state plasma levels are approximately 3- to 4-fold higher than levels observed after a single dose of ARIMIDEX. Plasma concentrations approach steady-state levels at about 7 days of once daily dosing. Anastrozole is 40% bound to plasma proteins in the therapeutic range."

It stands to reason that dosing less frequently than recommended (i.e. less than once daily) will result in lower steady-state drug concentrations in the body, which may decrease effectiveness.

Nevertheless, there have been preliminary studies evaluating the tolerability of dosing aromatase inhibitors (e.g. Arimidex) intermittently, and findings suggest that every other day dosing may be better tolerated with similar efficacy.

Additionally, studies evaluating off-label uses (e.g. for testosterone-induced gynecomastia in men) have used alternative dosing schedules.

Lastly, there are also plenty of anecdotal reports that can be found online regarding individuals using alternative dosing schedules for Arimidex with little to no apparent negative effects.

Nevertheless, it is important to remember that you should not change your prescribed dose/dosing schedule of Arimidex without first consulting with your doctor.

There is a lack of data on any other dosing schedule than once-daily dosing of Arimidex. Alternative regimens, if they are recommended at all, are most likely going to be used as a last resort, only if you cannot tolerate the indicated once-daily regimen.

Additional Information

There are no known interactions between Arimidex and foods, such as cruciferous vegetables.

However, it is thought that cruciferous vegetables can alter estrogen metabolism in the body. Whether or not you need to be on a certain diet or have certain dietary considerations with your diagnosis should be based on a conversation with your doctor.

References
  1. Cruciferous Vegetables and Human Cancer Risk: Epidemiologic Evidence and Mechanistic Basis. PubMed
  2. Intermittent dosing of aromatase inhibitors (AI) to improve tolerance in postmenopausal women: a rationale for future clinical studies. PubMed
  3. Arimidex Prescribing Information. AccessFDA
  4. Exemestane for breast-cancer prevention in postmenopausal women. PubMed
  5. Treatment of testosterone-induced gynecomastia with the aromatase inhibitor, anastrozole. PubMed

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