There are two possibilities you should seek to eliminate.

The first is to have your Vet stick a scope down into the stomach to check for possible ulcers. If one is found then treating with zantac or prilosec will help the healing. Not to mention avoiding any feeding of bones.

The second primary cause of blood in the vomit is the beginning of liver failure and/or disease. If caused by something like Salmonella contaminated meat, then the antibiotics should help-assuming they don't irritate an ulcerated stomach. Cephalexin has such a habit, where as Baytril is usually mild on the tummy. A liver blood profile should be taken, and if enzymes are elevated and the antibiotics are not clearing up the problem then you might want to have an ultrasound performed.