Naming is such a problem in the medical space, there are special provisions for trademarking medicines (class 5 marks), where they can be similar as long as they are used for very different ailments and there's no risk of confusion.

It's still extremely hard, see this PDF:

http://pubs.acs.org/subscribe/archive/mdd/v05/i08/pdf/802pat...

(Standard disclaimer - IANAL)