Oxacillin sodium (trade name Bactocill) is a narrow-spectrum beta-lactam antibiotic of the penicillin class developed by Beecham.

Oxacillin is a penicillinase-resistant β-lactam. It is similar to methicillin, and has replaced methicillin in clinical use. Other related compounds are nafcillin, cloxacillin, dicloxacillin, and flucloxacillin. Since it is resistant to penicillinase enzymes, such as that produced by Staphylococcus aureus, it is widely used clinically in the US to treat penicillin-resistant Staphylococcus aureus. However, with the introduction and widespread use of both oxacillin and methicillin, antibiotic-resistant strains called methicillin-resistant and oxacillin-resistant Staphylococcus aureus (MRSA/ORSA) have become increasingly prevalent worldwide. MRSA/ORSA is treated using vancomycin.

Acute bacterial meningitis predominantly affected adults and coagulase negative staphylococcus species were the common causative agent in Qatar with majority nosocomial infections. More than 90% of all implicated coagulase-negative staphylococci strains were oxacillin-resistant ¹⁾.