Foxitin Mechanism of Action

Pharmacology: Pharmacodynamics: Following an intravenous dose of 1 gram, serum concentrations were 110 mcg/mL at 5 minutes, declining to less than 1 mcg/mL at 4 hours. The half-life after an intravenous dose is 41 to 59 minutes. Approximately 85 percent of cefoxitin is excreted unchanged by the kidneys over a 6 hour period, resulting in high urinary concentrations. Probenecid slows tubular excretion and produces higher serum levels and increases the duration of measurable serum concentrations.
Cefoxitin passes into pleural and joint fluids and is detectable in antibacterial concentrations in bile.
In a published study of geriatric patients ranging in age from 64 to 88 years with normal renal function for their age (creatinine clearance ranging from 31.5 to 174 mL/min), the half-life for cefoxitin ranged from 51 to 90 minutes, resulting in higher plasma concentrations than in younger adults. These changes were attributed to decreased renal function associated with the aging process.
Microbiology: The bactericidal action of cefoxitin results from inhibition of cell wall synthesis. Cefoxitin has in vitro activity against a wide range of gram-positive and gram-negative organisms. The methoxy group in the 7α position provides cefoxitin with a high degree of stability in the presence of beta-lactamases, both penicillinases and cephalosporinases, of gram-negative bacteria.
Cefoxitin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the Indications and Caution for Usage.
Aerobic gram-positive microorganisms: Staphylococcus aureus^a (including penicillinase-producing strains); Staphylococcus epidermidis^a; Streptococcus agalactiae; Streptococcus pneumoniae; Streptococcus pyogenes.
^aStaphylococci resistant to methicillin/oxacillin should be considered resistant to cefoxitin.
Most strains of enterococci, e.g., Enterococcus faecalis, are resistant.
Aerobic gram-negative microorganisms: Escherichia coli; Haemophilus influenzae; Klebsiella spp. (including K. pneumoniae); Morganella morganii; Neisseria gonorrhoeae (including penicillinase-producing strains); Proteus mirabilis; Proteus vulgaris; Providencia spp. (including Providencia rettgeri).
Anaerobic gram-positive microorganisms: Clostridium spp.; Peptococcus niger; Peptostreptococcus spp.
Anaerobic gram-negative microorganisms: Bacteroides distasonis; Bacteroides fragilis; Bacteroides ovatus; Bacteroides thetaiotaomicron; Bacteroides spp.
The following in vitro data are available, but their clinical significance is unknown.
Cefoxitin exhibits in vitro minimum inhibitory concentrations (MICs) of 8 mcg/mL or less for aerobic microorganisms and 16 mcg/mL or less for anaerobic microorganisms against most (≥ 90%) strains of the following microorganisms; however, the safety and effectiveness of cefoxitin in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials.
Aerobic gram-negative microorganisms: Eikenella corrodens [non-β-lactamase producers]; Klebsiella oxytoca.
Anaerobic gram-positive microorganisms: Clostridium perfringens;
Anaerobic gram-negative microorganisms: Prevotella bivia (formerly Bacteroides bivius).
Cefoxitin is inactive in vitro against most strains of Pseudomonas aeruginosa and enterococci and many strains of Enterobacter cloacae.