If you don't need to keep the contact information "private" then you can
- create different groups, or
- use different sources
Depending on how you're already syncing contacts you can or can't use the second option. To help going further, it also would be helpful to know where the patients information is stored.
If you want to keep the patients information private, i.e. patients don't appear in any app apart the contact manager, then I suggest you to use a database-like app (not sure but Bento for example should be ok provided you DON'T use the contacts database that is synced to the address book).