Chemical formula: C₁₉H₁₇ClFN₃O₅S Molecular mass: 453.872 g/mol PubChem compound: 21319
Flucloxacillin is a narrow-spectrum antibiotic of the group of isoxazolyl penicillins; it is not inactivated by staphylococcal β-lactamases.
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 is stable in acid media and can therefore be administered either by the oral or parenteral route. The peak serum levels of flucloxacillin reached after one hour are as follows.
The total quantity absorbed by the oral route represents approximately 79% of the quantity administered.
After the intramuscular administration of a single 250 or 500mg dose of flucloxacillin to volunteers, mean peak concentrations of the drug in serum were approximately 10.5 and 16mg.l-1 respectively. Mean urinary excretion of flucloxacillin following its intramuscular use is 61% of the administered dose.
Flucloxacillin may also be administered by intravenous bolus injection or by slow intravenous infusion. High serum levels of the drug are achieved by these modes of administration: 30 minutes and 2 hours after a single 500mg intravenous bolus injection of flucloxacillin the mean serum concentration of the drug was 38 and 7.5mg.l-1, respectively; 30 minutes and 3 hours after a single 1g intravenous bolus injection of flucloxacillin, the mean serum concentrations were 60 and 4mg.l-1 respectively. The administration of 2g flucloxacillin by intravenous infusion over 20 minutes resulted in mean serum concentrations of 244 and 27.7mg.l-1 15 minutes and 120 minutes respectively after the end of the infusion.
Flucloxacillin diffuses well into most tissue. Specifically, active concentrations of flucloxacillin have been recovered in bones: 11.6mg/l (compact bone) and 15.6mg/l (spongy bone), with a mean serum level of 8.9mg/l.
Crossing the meningeal barrier: Flucloxacillin diffuses in only small proportion into the cerebrospinal fluid of subjects whose meninges are not inflamed.
Crossing into mothers' milk: Flucloxacillin is excreted in small quantities in mothers' 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.
Flucloxacillin is metabolised to a limited extent and the unchanged drug and metabolites are excreted in the urine by glomerular filtration and renal tubular secretion. Up to 90% of an intramuscular dose is excreted in the urine within six hours. Only small amounts are excreted in the bile.
Excretion occurs mainly through the kidney. Between 65.5% (oral route) and 76.1% (parenteral route) of the dose administered is recovered in unaltered active form in the urine within 8 hours. A small portion of the dose administered is excreted in the bile. The excretion of flucloxacillin is slowed in cases of renal failure.
The percentage of a dose of intravenous flucloxacillin recovered in urine in an 8 hour collection period varies from 60 to 76%.
About 95% of flucloxacillin in the circulation is bound to plasma proteins. Flucloxacillin has been reported to have a plasma half-life of approximately one hour. The half-life is prolonged in neonates.
The serum half-life of flucloxacillin in patients with severe kidney disease has been reported as 135 to 173 minutes. No significant difference in the half-life was found between patients on or off haemodialysis. Flucloxacillin is not removed by haemodialysis.
Flucloxacillin is unlikely to be excreted in breast milk to any significant extent. Similarly, placental transfer is unlikely to occur to any appreciable extent.
The serum protein-binding rate is 95%.
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