protect from special characters like "\"

[eluser]elite[/eluser]
Can you post some code - e.g. how are you constructing your queries?

I suspect you're not escaping your queries (which is bad from a security point of view as well as breaking your queries.

The active record class automatically escapes characters:
ellislab.com/codeigniter/user-guide/database/active_record.html

Alternatively you may want to look at escaping queries in the database library:
ellislab.com/codeigniter/user-guide/database/queries.html