If you have to wait for Furan II to get to you, in the meantime you can use tri-sulpha, or sometimes called triple sulpha. If nothing immediate is available, at least place it in a hospital tank with NEW water and excellent aeration, changing at least half the water daily.
Just in case you haven't started anything yet, you need to do something to remedy the original cause of this problem which almost always stems from poor water quality. Hobbyists can't test for this condition and even though testing that CAN be done shows everything to be OK, it is NOT.
I'd suggest reassessing your husbandry protocol, looking for places where hidden spots are trapping uneaten food/detritus and increasing the frequency of your water changes and tank cleaning.
This water quality problem usually results from occasional lapses of husbandry over a period of time, slowly degrading conditions, not a sudden occurrence.