A 53 year old man with non-insulin dependent diabetes mellitus presents with pain, redness, and swelling of the right foot and lower leg, accompanied by a temperature of 102. X-rays reveal no subcutaneous gas and show no evidence of osteomyelitis. The patient has been admitted on three previous occasions for cellulitis of the right foot and notes that this episode is identical. Which of the following antibiotics is the most appropriate initial therapy for a presumed diagnosis of cellulitis?
1) oral dicloxacillin
2) intravenous nafcillin
3) intravenous gentamicin
4) intravenous ampicillin-sulbactam
5) intravenous cefazolin