My Mother Has Atrial Fib. Her Cardio Took Her Off

My mother has atrial fib. her cardio took her off tikosyn Thursday and told her to start flecainide on Monday. She is also taking Cardizem daily. We are concerned about her starting flecainide. does this medication need to be started in hospital setting like tikosyn?? What about interaction with cardizem?? what about toxicity?? please advise