Solubility, absorption and toxicity are certainly all the concerns when using
mammal antibiotics in fish tanks. Tetracycline, sulfa antibiotics and metronidazole are all antibiotics that are used on fish as well as mamals. The only one that I have seen in the exact same form packaged for fish and mammals is oxitetracycline.
Dose according to Noga: 40-380mg (large dose range) per gallon of water. Treat for 3 days, then do a 50% water change before any further treatment.
Personally, I would order a 'fish' prep from an online site and I would treat in a QT/HT .