Flucloxacillin is an isoxazolyl penicillin of the β-lactam group of antibiotics, which exerts a bactericidal effect upon many Gram-positive organisms including β-lactamase-producing staphylococci and streptococci. While no longer used in the United States, Flucloxacillin is supplied under a variety of trade names in other countries, including Floxapen, Flopen, Staphylex. Floxapen is indicated for the treatment of infections due to sensitive Gram-positive organisms, including β-lactamase-producing staphylococci and streptococci. Typical indications including, skin and soft tissue infections; respiratory tract infections; other infections caused by floxapen-sensitive organisms, like example, osteomyelitis, urinary tract infection, septicaemia, endocarditis. Floxapen is also indicated for use as a prophylactic agent during major surgical procedures when appropriate; for example cardiothoracic and orthopaedic surgery. Flucloxacillin, by its action on the synthesis of the bacterial wall, exerts a bactericidal effect on streptococci except those of group D (Enterococcus faecalis) staphylococci. It is not active against methicillin-resistant staphylococci. There is evidence that the risk of flucloxacillin induced liver injury is increased in subjects carrying the HLA-B*5701 allele. Despite this strong association, only 1 in 500-1000 carriers will develop liver injury. Consequently, the positive predictive value of testing the HLA-B*5701 allele for liver injury is very low (0.12%) and routine screening for this allele is not recommended. Flucloxacillin diffuses well into most tissue. Specifically, active concentrations of flucloxacillin have been recovered in bones: 11.6 mg/L (compact bone) and 15.6 mg/L (spongy bone), with a mean serum level of 8.9 mg/L. Flucloxacillin diffuses in only small proportion into the cerebrospinal fluid of subjects whose meninges are not inflamed. It is also excreted in small quantities in mother's milk. In normal subjects approximately 10% of the flucloxacillin administered is metabolised to penicilloic acid. The elimination half-life of flucloxacillin is in the order of 53 minutes.