Pharmacokinetics of flucloxacillin and its metabolites in patients with renal failure: Impact on liver toxicity
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OBJECTIVE: The antimicrobial agent flucloxacillin is a potential cause of drug-induced liver disease, but the underlying mechanisms for toxicity have not been fully elucidated. As in-vitro and in-vivo findings suggest that biotransformation products contribute to hepatotoxicity, the purpose of this study was to characterize formation and accumulation of its metabolites in patients with renal failure.

METHODS: Twelve intensive care patients undergoing continuous venovenous hemofiltration received 4.0 g flucloxacillin as single and repeated infusion. Blood and dialysate samples were collected and analyzed for flucloxacillin and its metabolites by HPLC.

RESULTS: The overall amounts of the flucloxacillin metabolites 5'-hydroxymethylflucloxacillin (5-OH-FX), 5'-hydroxymethylflucloxacillin-penicilloic acid (5-OH-PA), and flucloxacillin-penicilloic acid (FX-PA) produced varied considerably between patients, and accounted for 3.62 - 35.9% of total flucloxacillin concentration (flucloxacillin + metabolites) in the plasma. Clearance rates and sieving coefficients for 5-OH-FX and FX-PA were comparable to that of the parent drug, although removal of 5-OH-PA was decreased. Using an isolated perfused rat liver model we demonstrated that 5-OH-FX reached concentrations in the bile (240.5 ± 84.2 nmoles/mL) that were sufficient to exert cytotoxic effects, unlike either of the two penicilloic acids.

CONCLUSIONS: Based on data from perfused rat livers, high biliary concentrations of 5-OH-FX might also be observed in our patients explaining why LDH, bilirubin, and alkaline phosphatase were elevated in up to 8/12 patients after repeated infusion of flucloxacillin. Liver toxicity of flucloxacillin might therefore be observed in patients with renal impairment after continuously elevated 5-OH-FX levels.
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