Staphylococcus epidermidis and S. aureus are the most common causes of bacterial endophthalmitis. A study of the penetration of selected antistaphylococcal antibiotics into human vitreous was undertaken in 58 patients. After 2-g intravenous doses of cephalothin, cefazolin, methicillin, oxacillin, or nafcillin were given to patients about to undergo vitreous surgery, mean vitreous levels for each antibiotic were as follows: cephalothin, 0.97 μg/ml in diabetics and 0.69 μg/ml in nondiabetics; cefazolin, 0.84 μg/ml in diabetics and 1.6 μg/ml in nondiabetics; methicillin, 2.56 μg/ml in diabetics and 2.64 μg/ml in nondiabetics; oxacillin, 0.62 μg/ml in diabetics and 0.34 μg/ml in nondiabetics; and nafcillin, 0.73 μg/ml in diabetics and 0.75 μg/ml in nondiabetics. Only cefazolin produced vitreous concentrations consistently above its minimum inhibitory concentration for 90% of S. epidermidis isolates. Staphylococcus aureus isolates were not similarly covered. There was a trend toward higher vitreous antibiotic concentrations in patients with proliferative vitre-oretinopathy and rubeosis.
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