Why are dosages for estrogen suppression drugs one-size-fits-all?

Posted by gldilli @gldilli, Mar 28, 2023

Why is the dosage for Anastrozole (and any other AI) the same for everyone no matter your weight or size? Does this-one size-fits-all approach have an impact on side effects, risk of recurrence, etc. I’d like to know what the medical community has to say.

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@cashemire

Thanks for posting this info and link! I would really like to find the original article with the clinical data. I came across a 1996 article, very small groups, also about dosing and am wondering about the 'below level of detection' difference betw .5 and 1 mg of Arimidex, but which is mentioned that result found 24 hrs after last dose...so doesn't explicitly mention if that was also the case during the 14-day testing period....(study funded by Zeneca, btw)

Arimidex (ZD1033): a selective, potent inhibitor of aromatase in postmenopausal female volunteers
RA Yates', M Dowsett2, GV Fisher', A Selen3 and PJ Wyld4 'Zeneca Pharmaceuticals, Alderley Park, Macclesfield, Cheshire SKIO 4TG, UK; 2Royal Marsden Hospital, Fulham Road, London, SW3 6JJ, UK; 3Zeneca Pharmaceuticals, 1800 Concord Pike, Wilmington, USA; 4Inveresk Clinical Research Ltd, Riccarton, Edinburgh, UK.
Summary
Two multiple-dose studies were conducted in healthy post-menopausal female volunteers to investigate the pharmacokinetics and effects on endocrinology of Arimidex (ZD1033). Volunteers in the first trial were dosed with 3 mg of ZD1033 daily over 10 days to assess the effects on endocrinology of ZD1033 and establish the pharmacokinetic profile. In the second trial volunteers received 14 daily doses of either 0.5 or 1.0 mg of ZD1033 to assess the pharmacokinetics of ZD1033 and the effects of low doses of ZD1033 on serum oestradiol concentrations. Following multiple dosing a significant reduction in the concentration of serum oestradiol of approximately 80% of baseline was obtained with all three doses; no recovery in oestradiol was apparent for up to 144 h after the last dose. There was no overall difference in the level of oestradiol suppression between the 0.5 or 1.0 mg doses of ZD1033. However, comparison of the number of volunteers with oestradiol concentrations below the limits of detection of the assay, 24 h after the last dose of ZD1033, suggested that 1.0 mg was the minimal dose required for maximal suppression of oestradiol.

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My conclusion from this sentence in this study "There was no overall difference in the level of oestradiol suppression between the 0.5 or 1.0 mg doses of ZD1033." is that .5mg works just as well as 1.0mg. The only difference happens after the last dose. I've been on Arimidex since March 1st (I had bi-lateral breast cancer - stage 1, ER+ but HERC- in both breasts which were treated by lumpectomy and radiation). I have always been an athlete and eaten well. I have night sweats and terrible pains in my fingers from the Arimidex. I have played with taking it at different times of the day and with/without food as it made me really nauseous at first. I would like to see more studies about taking a half dose of Arimidex.

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Been on Letrozole since March 2023.
Have osteo arthritis of both knees and now am dealing with muscle pain in left calf to knee.
Also have osteoporosis.

I also read on Mayo Clinic Connect of the person who had muscle shrinkage and ended up in a wheelchair because they had the rare side effect of that from taking Eliquis.” Which I have been taking since 4/02/22.

What specialist can figure this out?

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@southgawalker

Thank you for planning to share the articles. My symptom is left leg pain and now left jaw pain when eating. These seem very odd and may not be related.

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Hi I’d get that checked asap. Just in case it’s heart related. My symptom is my back and it’s / weeks today since I stopped Anastrozole my back in no better. In fact I think it’s a bit worst x

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Thank you for sharing your experience. I found it very interesting. There are few references to jaw pain as a side effect of anastrozole. After taking anastrozole 6 weeks, I also developed jaw pain when eating. I did not see it listed as a side effect, so I did not think it was related to this drug. I thought that I had TMJ, so I made an appointment to see an ENT specialist. I was experiencing many other side effects from anastrozole, so I had stopped taking it after 2 1/2 months. I saw the ENT 2 1/2 weeks after stopping anastrozole. By then, my jaw pain had subsided substantially. The ENT said that my jaw pain was not caused by TMJ. Joint pain is a well-known side effect and the jaw is a joint. Estrogen protects joints and reduces inflammation. When an aromatase inhibitor lowers estrogen to undetectable levels, it seems to me that any joint could be affected.
BTW - My former oncologist would not acknowledge that my jaw pain or any of my other numerous side effects could be caused by anastrozole. However, they all went away after I stopped taking it. I now have a wonderful new oncologist.

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@bloncape

Thank you for sharing your experience. I found it very interesting. There are few references to jaw pain as a side effect of anastrozole. After taking anastrozole 6 weeks, I also developed jaw pain when eating. I did not see it listed as a side effect, so I did not think it was related to this drug. I thought that I had TMJ, so I made an appointment to see an ENT specialist. I was experiencing many other side effects from anastrozole, so I had stopped taking it after 2 1/2 months. I saw the ENT 2 1/2 weeks after stopping anastrozole. By then, my jaw pain had subsided substantially. The ENT said that my jaw pain was not caused by TMJ. Joint pain is a well-known side effect and the jaw is a joint. Estrogen protects joints and reduces inflammation. When an aromatase inhibitor lowers estrogen to undetectable levels, it seems to me that any joint could be affected.
BTW - My former oncologist would not acknowledge that my jaw pain or any of my other numerous side effects could be caused by anastrozole. However, they all went away after I stopped taking it. I now have a wonderful new oncologist.

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This is important. I’ve found that we all have combinations of different symptoms after taking this pill. The fact that your jaw pain wasn’t listed, doesn't mean it’s not a side effect. I have found that I can’t expect my regular doctor…who is great..or my dentist to be informed regarding anastrozole and what it can do to your body. I do expect them to listen to concerns and take them seriously, not brush them aside because they aren’t on a list.

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@bloncape

Thank you for sharing your experience. I found it very interesting. There are few references to jaw pain as a side effect of anastrozole. After taking anastrozole 6 weeks, I also developed jaw pain when eating. I did not see it listed as a side effect, so I did not think it was related to this drug. I thought that I had TMJ, so I made an appointment to see an ENT specialist. I was experiencing many other side effects from anastrozole, so I had stopped taking it after 2 1/2 months. I saw the ENT 2 1/2 weeks after stopping anastrozole. By then, my jaw pain had subsided substantially. The ENT said that my jaw pain was not caused by TMJ. Joint pain is a well-known side effect and the jaw is a joint. Estrogen protects joints and reduces inflammation. When an aromatase inhibitor lowers estrogen to undetectable levels, it seems to me that any joint could be affected.
BTW - My former oncologist would not acknowledge that my jaw pain or any of my other numerous side effects could be caused by anastrozole. However, they all went away after I stopped taking it. I now have a wonderful new oncologist.

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I phoned breast care in York yesterday and explained my situation. I don’t want to go back to my old oncologist either!! He is very arrogant and doesn’t listen!! I stopped taking it 2 weeks ago but pain in my back is worse not better!! I’m hoping breast care,, who are looking into my meds etc will come up with a solution. My gp surgery is useless.,

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I tried all five of my oncologist's estrogen blockers. could not go on living like that. eczema was so awful I was on prednisone. I am post menopausal. asked what my estrogen level was? oncologist did not know? can you find out?... no...
went to pop with same question , she included it in regular blood work. my estrogen levels are below the charts???>. My pcp is both m.d. and naturopath. I am taking DIM and calcium glaurate, hoping for the best.

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@laurapix I was on Anastrozole and like you - no baseline of estrogen before surgery (mastectomy) or starting Anastrozole or even the 2 3/4 yrs I took it. Oncologist and PCP do not have any knowledge about correlation between effectiveness of Anastrozole and estrogen levels. I know this because I FINALLY got my oncologist to order an estrogen test and the result was ‘< 0’ He could definitively tell me what that meant in relationship to me taking Anastrozole. It literally meant nothing. One oncologist told me when I asked him “how do you know it’s working?” ‘We just take it for granted’. Wrong answer. I left him. I think we are the test subjects.

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@ginip

Indeed ‘one size fits all’ is the first abstract question that probably occurs to all and rightfully so. Once you find this understanding - your deeper needs and understandings are regarding side effects and are the challenge confronting us. Making your search concerning each side effect is the toughest endeavor. Prioritizing them, dealing with what you can. Collaboration can be helpful - or it can be another side effect in your need to make the decision for YOU!

This is the extra layer of understanding and concern that is preaching to the choir - fair enough if that is all you can offer. 🤷🏼‍♀️

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❤️❤️👍🏻

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It would cost too much for the pharmaceutical companies to test for all these combinations so they come up with a number that is not right for everyone - an average.

After having an awful experience with full dose of letrozole, I'm now being given anastrozole. Against my doctor's wishes, I was taking a half dose each day. Then I found this paper
https://aacrjournals.org/cancerres/article/75/9_Supplement/P1-12-15/606865/Abstract-P1-12-15-Intermittent-dosing-of-aromatase

and found for older women like me, half dose isn't a good idea - better to take it every other day.
So far not having any problems.

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