Then try calling some carpet stores in your area for some ideas. You could also try calling the cough syrup manufacturer and ask THEM. I don't know what else to suggest, you say NO CLEANING PRODUCT will take it out. By defintion, your question prevents any suggestions from being offered, because we don't know what you have or haven't tried. We also don't know what combinations of cleaning products you may have put on this puppy that are now preventing anything else from working.
There is one last solution I will offer, and that is that ServiceMaster (The guys with the bright yellow and green trucks) is better at removing stains and doing fire recovery work than anyone I know. You could have one of them come out to take a shot at it, they are pretty danged good.
Good luck, and take that nasty stuff over the kitchen sink.