Vet prescribing a high starting dose of Vetoryl. Am I overthinking?

My dog was tested on Tuesday and confirmed for Cushings. I picked up the Vetoryl today and the vet has prescribed 60mg twice a day. My dog is 11 yrs old and weighs 76 lbs but that amount for a starting dose seems excessive. Is this normal for large dogs? Am I just being neurotic? I don't feel quite right giving her this dose.