My girl Kiya is on seizure meds which wreaks havoc on the liver, her numbers average in the 350 range, talk to you vet about adding milkthistle into her diet. I have kept Kiya's numbers down considering she's been on the meds since 2005. There is also a liver cleansing diet that you can look into.
Apache - Shiloh Shepherd 12/15/02
Kiya - Shiloh Shepherd 5/15/04
Lakota - WGSD 1/13/10