The most effective immediate suicide prevention available is a surprising one. It's Ketamine. It takes effect very rapidly and the anti-depressant effects persist for months from a single dose. It's a wonder how SSRI's are in wide use when there are far more effective treatments which have been around since the 60's. Marketing and business are to blame for that, I suppose.

http://www.medicalnewstoday.com/articles/251220.php

There are also some novel NMDA antagonists (same mechanism as Ketamine) in the works, which come with less perception alterations, the names of which escape me, which will change things for the better for a lot of people.