What can you use to get the odor of cat spray or urine out of carpets?

We just moved into a new apartment and the people before us had cats it smells like the cats just sprayed or used the carpets as the bathroom instead of a litter box. The amonia smell is so powerful it makes our eyes and throat burn. I have a ton of severe allergies and need to find some type of chemical or mixture that will permanently get rid of the odor. PLEASE HELP!!!