Oxacillin (trade name Bactocill) is a narrow-spectrum beta-lactam antibiotic of the penicillin class developed by Beecham. It was patented in 1960 and approved for medical use in 1962. Medical uses 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 can be treated with vancomycin or other new antibiotics. Contraindications The use of oxacillin is contraindicated in individuals that have experienced a hypersensitivity reaction to any medication in the penicillin family of antibiotics. Cross-allergenicity has been documented in individuals taking oxacillin that experienced a previous hypersensitivity reaction when given cephalosporins and cephamycins. Adverse effects Commonly reported adverse effects associated with the use of oxacillin include skin rash, diarrhea, nausea, vomiting, hematuria, agranulocytosis, eosinophilia, leukopenia, neutropenia, thrombocytopenia, hepatotoxicity, acute interstitial nephritis, and fever. High doses of oxacillin have been reported to cause renal, hepatic, and nervous system toxicity. Common to all members of the penicillin class of drugs, oxacillin may cause acute or delayed hypersensitivity reactions. As an injection, oxacillin may cause injection site reactions, which may be characterized by redness, swelling, and itching. Pharmacology Mechanism of Action Oxacillin, through its β-lactam ring, covalently binds to penicillin-binding proteins, which are enzymes involved in the synthesis of the bacterial cell wall. This binding interaction interferes with the transpeptidation reaction and inhibits the synthesis of peptidoglycan, a prominent component of the cell wall. By decreasing the integrity of the bacterial cell wall, it is thought that oxacillin and other penicillins kill actively growing bacteria through cell autolysis. Chemistry As with other members of the penicillin family, the chemical structure of oxacillin features a 6-aminopenicillanic acid nucleus with a substituent attached to the amino group. The 6-aminopenicillanic acid nucleus consists of a thiazolidine ring attached to a β-lactam ring, which is the active moiety responsible for the antibacterial activity of the penicillin family. The substituent present on oxacillin is thought to impart resistance to degradation via bacterial β-lactamases. History Oxacillin, a derivative of methicillin, was first synthesized in the early 1960s as part of