My wife was bitten by some sort of insect. it appears to be a spider bite. red cellulitis that is spreading, center is open draining. what antibiotic?

See doctor ASAP: My guess is that this isn't from an insect bite, but that part doesn't matter. It isn't possible to judge the best antibiotic except by in-person exam and maybe testing. Your wife should not treat herself for this, needs to see a doctor immediately. If her own doctor can't see her right away, she should go to an urgent care clinic or emergency room.

See your doctor: Skin infections are most commonly caused by S. aureus or "staph." The resistant form is known as MRSA. Antibiotic choice depends on the patient's other medical problems but Cephalexin is a common choice for the non-resistant form and Doxycycline and Linezolid are the most effective oral antibiotics for MRSA. Your provider can culture the wound to tailor antibiotics specifically to the infection.