I really recommend Marin as it also contains Vitamin E. If you give milk thistle alone you have to give Vitamin E separately.
I absolutely swear by milk thistle. Lady has to take the highest possible dose of pheno for her size because she has cluster seizures. We also had to add potassium bromide to control them, although that isn't processed through the liver. As I said, Lady's vet is amazed that her ALT is only 79 after 10+ years on such a high dose of pheno.
I get it from Entirely Pets. Diego will only need 1/4 tablet so a bottle will last you several months.
Marin for Small to Medium Dogs (30 Tablets)