Flucloxacillin, a type of penicillin, is the most commonly used antibiotic tablet for cellulitis. If you are allergic to penicillin, you may be given clarithromycin. The choice of antibiotics will depend on local guidelines. See your doctor as they can advise you as to which antibiotic is appropriate for you. Most cases of cellulitis are treated with a week of antibiotic tablets. If the infection has not fully cleared after one week, you may need a second week of antibiotics. If antibiotic tablets are not helping, you may be given antibiotics through a vein (intravenous).