To jardinera25: I'm not a doctor.
1. I found scientific research for AIs by Googling "Alternative dose for...". I didn't look for Fulvestrant.
2. For me, atorvastatin combined with anastrozole and ribociclib raised liver enzymes greatly and greatly increased muscle pain. Stopped atorvastatin. Muscle pain disappeared in days. Liver values took weeks to come down.
3. Some take Claritin (loratadine) and/or tart cherry juice for AI pain, since some say AI pain is caused by increased histamines. I haven't tried it. Worth researching in your case, IMHO.
4. Since your cancer treatment is working, maybe Claritin would help and no dose reduction of cancer meds would be needed--my personal opinion--I'm not a doctor.
Best of luck!