Flucloxacillin sodium is a highly active antibiotic against Gram-positive and Gram-negative bacteria. IC50 & Target: Bacterial^[1] In Vivo: The serum elimination half-life of flucloxacillin is 1.31-1.39 hours, and six hours after administration of a single 250 mg dose the serum concentration of flucloxacillin is 0.46 micrograms/mL^[1]. Oral flucloxacillin does not affect sweat electrolytes and is not a contraindication to sweat testing^[2]. Flucloxacillin has been reported to be metabolized in man to the penicilloic acid, the antibacterially active 5'-hydroxymethyl derivative and the penicilloic acid of the 5'-hydroxymethyl derivative. The metabolism of flucloxacillin in the rat is similar^[3].