Taking Milk Thistle in Cushing's Disease

My "Scottie Dog" has Cushings Disease and was on medication for the adrenal gland. Now that the adrenal gland is not functional, he is on Prednisone and is taking Florifef. Upon taking blood test, he also has a very high count for his liver. I would like to start giving him milk thistle. Would giving him milk thistle have an effect with the other medicines he is taking?

I have no experience with animal medicine, but milk thistle has been extensively tested on animals with only positive results.
Milk thistle detoxifies, protects the liver, accelerates the regeneration of new liver cells and acts as an antioxidant. No toxic effects have been reported and there are no known interactions with other herbs or drugs.
Prednisone suppresses inflammation. Florinef maintains the sodium balance in adrenal insufficiency by promoting sodium re-absorption by the kidney.
Both drugs are metabolized by the liver, as are most drugs, so there is a heavier workload on the liver when taking drugs.