Gregory Lewbart published Invertebrate Medicine, 2006. The section on cephalopods, while very short, lists several possible treatments. Baytril, or enrofloxacin, can be administered intra-venous, orally, or in a bath. The oral dosages are 10 mg/ kg and the bath dosage is 2.5 mg/ L for 5 hours. Be cautious with the dosage as these dosages, as of 2006, are still only empirical values. Keep a close watch on the ventilation rate and overall behavior and if anything seems abnormal, discontinue the treatment immediately.
I would not say that this book is necessary for cephalopod keepers because out of the 350 pages, only 20 are devoted to cephalopods. But it has good information in those 20 pages. It is also very indicative of what we still don't know about cephalopod disease and treatment. It also has information on other invertebrates that can be used with cephalopods. If you have an extra $150 bucks then get the book.
Good Luck
Greg