Which antibiotic combination should be given in cellulitis

One of my patients, a 70-year-old lady has cellulitis of right lower leg. She is mild obese not a diabetic or hypertensive. No COPD or any chronic dermatoses. Her TFT KFT LFT are normal.

CBC shows mild leucocytosis. Duplex scan also normal. Now she is on ceftriaxone, metronidazole and amikacin for 5 days.No response. Kindly suggest me the best combination of antibiotics for this patient.