Cephalosporins are probably the best antibiotic's for a skin infection. I would be sure that your vet has cultured the area affected to make sure what is growing in there also. This will cut out the uncertainty of the best antibiotic to cear it up the fastest. Also know that he will probably have to be on meds for 4-6 weeks. You have to understand that the skin is the largest organ in the body....this being said, it takes a long time to clear up.

Ok....here's a trick that may work. I would make boiled ground beef . Make small meatballs or large grape size pieces once it is cooked. The trick is to give him a few without medication so he has the chance to check them for meds...once you have gained his trust with them...give him one after another quickly and once he's gulping them down without hestitation, slip in the medicated ball. Be sure to have it made up prior to starting this so you can slip it in to the mix without missing a beat.

Hope this works and let me know if you have any other questions.