Jim since you started the kanamycin did it continue to get larger?
I would suggest netting the fish and swabbing the hole with iodine or hydrogen peroxide .. .
If the infection isnt responding to the kanamycin then it may not be the right medicine.. it may be better to try a different one. maracyn 1 and 2 combined is usually very effective on difficult bacterial problems... at the least maracyn 2 is woth trying(minocycline).
I would separate the fish though... if thats from one of the fin rot bacterias it can be very contagious.
al