@crazyhazy, kidney function is something that doctors keep a close eye on. There are many drugs that can have a temporary or permanent impact on the kidneys, even drugs like over-the-counter pain medications like aspirin, naproxen and ibuprofen. The following breast cancer treatments can have an affect on the kidneys:
- Paraplatin (carboplatin)
- Afinitor (everolimus)
- Avastin (bevacizumab)

Whether Arimidex (anastrozole) is the culprit or not, it is good that your doctors are monitoring your creatine levels. Did you have kidney issues before breast cancer?