Docs will often prefer to switch AIs rather than dose adjust for side effects because they prefer to stick with approved doses. I'm also in Kisqali where starting dose is 600mg daily. Because of neutropenia, dose was reduced to 200mg. Since we all metabolize meds differently and may be taking other meds that slow metabolism, my 200mg may lead to same concentrations as 600mg in someone else. I was diagnosed at stage 4 with lobular carcinoma and have been at this dose for 3 years. Fingers crossed.