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Pharmacology: Cefuroxime is a β-lactam type antibiotic. More specifically, it is a second-generation cephalosporin. Cephalosporins work the same way as penicillins: they interfere with the peptidoglycan synthesis of the bacterial wall by inhibiting the final transpeptidation needed for the cross-links. This effect is bactericidal. Clavulanic acid is a mechanism-based β-lactamase inhibitor.
Cefuroxime has bactericidal activity against a wide range of common pathogens, including beta-lactamase producing strains. The bactericidal action of cefuroxime results from inhibition of cell wall synthesis by binding to essential target proteins. Cefuroxime has good stability to bacterial beta-lactamases.
Clavulanic acid is a naturally derived beta lactamase inhibitor produced by Streptomyces clavuligerus. Clavulanic acid binds to and inactivates them thus preventing the destruction of cefuroxime that is a substrate for this enzyme. It has poor intrinsic antimicrobial activity, but it is an irreversible binder of β-lactamases produced by a wide range of gram positive and gram negative microorganism.
Pharmacokinetics: After oral administration cefuroxime axetil is absorbed from the gastrointestinal tract and rapidly hydrolysed in the body to release cefuroxime into the circulation. Approximately 60% of an administered dose is absorbed. Optimum absorption occurs when it is administered after a light meal. Absorption is not decreased by drugs which affect gastrointestinal motility e.g. loperamide, diphenoxylate or castor oil. However, absorption is decreased by concurrent administration of drugs such as ranitidine.
The mean peak serum level of cefuroxime following a 250 mg dose in normal healthy adults, after food, was 4.1 mg/L and occurred two to three hours after dosing. Serum levels were significantly higher in the elderly, apparently due to slower excretion. Unhydrolysed drug was not detected in the serum but 1-2% of the administered dose is excreted in the urine in a form which indicates that small amounts of the intact ester are absorbed into circulation. The mean serum half life of cefuroxime is approximately 1.2 hours. Protein binding has been variously stated as 33-50% depending on the methodology used. Cefuroxime is not metabolized to any significant extent.
Excretion occurs mainly through the kidney both by glomerular filtration and tubular secretion. Approximately 49% of an administered dose, after food, is recovered in the urine in 24 hours; urinary recovery is significantly reduced if the drug is taken on an empty stomach.
After 250 mg dose urinary concentrations at0-6 and 6-12 hours were 227 mcg/mL (range 92-515) and 35.3 mcg/mL (range 7.6-102) respectively. Concurrent administration of probenecid prolongs the terminal half life of cefuroxime. Serum levels of cefuroxime are reduced by haemodialysis.
