Why does it take so LONG for doctors to reply!

It would be two weeks this Saturday that Brextin has had a seizure - however today he has had many - I have asked our neuro at Rochester Mayo to put him on the name brand drug instead of the generic brand of Keppra - but it is taking him forever to get it prescribed (first it was our insurance that was slowing the process down and now we are just waiting for our doctor to write a letter in support of trying the name brand drug) - it will be two weeks very soon - he is a well known doctor so he is out of the state or even country quite often - so I usually have to wait and wait until I hear back from him - I hate the waiting - my son is hurting because of the wait!!