The fundamental pathology of an ulcer is one of local ischemia therefore, any antibiotic in the bloodstream will not reach the ulcer
Topical antibiotic use is strongly discouraged
The organisms isolated from swabs of ulcers may represent what is present in the ulcer rather than what is invading nearby tissue
The complications of ulcers (cellulitis, osteomyelitis, etc.) should be managed as normal but it must be understood that antibiotic treatment is being given for these reasons NOT for the ulcer
Where there is evidence of infection seek specialist advice from Vascular surgery