My Husband Has Late Stage Parkinson's And Or Multiple System

My husband has late stage Parkinson's and or multiple system atrophy. He takes carbolic levo 25/100 3 tabs 5 times a day. None of the other Parkinson's drugs did anything. He also has severe postural hypotension with b/p often as low as 65/40 during the day pulse in 50-60s. Wondering if adding hyoscyamine to help control muscle "freezing" is a reasonable idea. Will runitpast our neurologist but need some input. D