Hi Alan,
Normally Pred is one of the best available medication against MG, it's effective and rather fast acting.
The usual maximum dosage is 1 mg/kg of weight/day. But due to the negative side effects associated with it, Pred is after a while tapered down to the minimum where symptoms reoccur.
You have thus to take something else to counteract the antibodies: immunodrepressors (Cellcept, Imuran,…) which are slow in action but which can relay Pred later on.
Take care,
Maurice.