I know this is months old but it is stated in many trusted forums and guides numerous times that you can gain a synergistic effect when using Kanamycin and Doxycycline together for infection. Yes mixing meds should not be the first thing tried but for stubborn infection when you do not know the cause it is very beneficial. Sometimes there are more than one cause for the symptoms and treating it all is needed. Same with Kanamycin and Furan-2, the synergistic thing, only you can't get the Furan-2 now. Nitrafurazone is still sold in a yellow powder on a certain reputable hobbyist site that also gives lots of info, and from some other fish stores but I am not sure I am allowed to post those specifics so go looking, have to spend time going through the many pages sometimes. For that combo above you can also use Metroplex. The three together are used for really hard to treat cases. I "think" Metro works with The Kana/Doxy mix as well? Not 100% on that but Metro can be combined safely with each individually. The Doxycycline ( Fin and Body) treats gram positive and some gram negatives and is a good broad spectrum antibiotic. The kanamycin is a great for internal bacterial and some fungal infections, it's strong so not to be used more than indicated.