[Becky]

Although all three AIs reportedly work the same clinically, there are differences on how they work biochemically. Femara and Arimidex work in the exact same biochemical pathway to inhibit the action of aromatase (an enzyme that is needed to facilitate the conversion of androgens to estrogen in the body by either the adrenal gland or body fat - hence why one must be post menopausal to take them because these drugs don't inhibit the production of estrogen by the ovaries).

Aromosin also inhibits aromatase but in an entirely different mechanism.

I have never really seen any of these drugs not work but maybe for you, one mechanism works better than another.

For example, (and I will really have to look to find the study), there is a study on metastatic women who failed on Arimidex. Astra Zeneca was the only maker of this drug at the time (as it is now generic too). So Astra Zeneca (AZ) started a study on women who failed Arimidex. Half of the women went on Faslodex, another AZ drug for ER+ women (but it is a drug that is injected monthly. I think initially a woman needs a shot 2 weeks apart and then monthly thereafter) and the other half of the women switched to Aromosin. The results were equal, both Faslodex and Aromosin worked equally as well for the women it worked for (as you know, any trial drug doesn't work for everyone). So for AZ, this was bad news as they were (I'm sure) hoping that Faslodex would work better than Aromosin since they make Faslodex too. So it was good news for Pfizer (Aromosin's maker) because why wouldn't a woman just not want to switch to another daily pill.

That said, why did you have to switch from Femara? Did it not work well for you or was it side effects? If it was side effects, many women have switched from Femara to Arimidex or vice versa and did see results (less side effects). I am just thinking out loud here for you because if it was side effects, and Femara seemed to be working, maybe it is the biochemical mechanism of which Arimidex's mechanism is the same as Femara's. Otherwise, you also have the advantage of the possibility of Faslodex as well (again ideas to go over with your medical team).

I hope this helps alittle bit. I do tend to sometimes go overboard with the science - that I know!!!