I have been prescribed 50000 unit of vitamin d to take twice a week. is that too much?

Yes: Absolute max is 2000iu/day. Too much is bad for you.

Possibly too much.: Taking 50, 000 units of vitamin d twice a week would be appropriate if your vitamin d serum level (25ohd) is very low or undetectable. After several weeks the serum 25ohd should be checked and if normal a lower daily dose such as 1-2000 units daily would be appropriate for chronic use.