Brazilian red propolis in combination with ß-lactams exerts an efficient antibacterial action over methicillin-resistant Staphylococcus aureus (MRSA) strains.

AIMS: The antibacterial activity of red propolis extract (RPE) and brown propolis extracts (BPE) and the synergistic effect of RPE with cefoxitin (CEFO), imipenem (IMI), and ertapenem (ERTA) was evaluated in vitro against methicillin-resistant Staphylococcus aureus (MRSA) strains. METHODS AND RESULTS: MRSA ATCC 33591, community-associated (CA-MRSA) USA300, and four clinical isolates were used. A broth microdilution assay was performed to obtain inhibitory and bactericidal concentrations of BPE, RPE, CEFO, IMI, and ERTA. RPE in combination with CEFO, IMI, and ERTA was evaluated on the formation or eradication of biofilm. The bacterial relative membrane conductivity of the strains was assessed after RPE and combinations exposition. Surface/binding computational analyzes between RPE compounds and penicillin binding protein 2a (PBP2a) were performed. BPE samples had no activity against MRSA (MICs 3.2-5 g l-1; MBCs 10-15 g l-1), so the subsequent assays were carried out only with RPE and antimicrobials. RPE exerted a bacteriostatic action (MICs 0.0156-0.125 g l-1; MBCs 0.5-2 g l-1) but the combinations with IMI and ERTA showed the highest inhibition, as observed in the time-kill curve. However, the FICI index showed synergism (≥0.5) only to RPE + IMI. This combination was the most effective in inhibiting the biofilm and showed the highest values of membrane conductivity. Computational predictions indicated that RPE constituents may interact with PBP2a. CONCLUSION: RPE and RPE + IMI exerted an antibacterial and antibiofilm activity on MRSA strains probably due to membrane/wall damage and interactions with PBP2a.

Exploring the Role of L10 Loop in New Delhi Metallo-ß-lactamase (NDM-1): Kinetic and Dynamic Studies.

Four NDM-1 mutants (L218T, L221T, L269H and L221T/Y229W) were generated in order to investigate the role of leucines positioned in L10 loop. A detailed kinetic analysis stated that these amino acid substitutions modified the hydrolytic profile of NDM-1 against some ß-lactams. Significant reduction of kcat values of L218T and L221T for carbapenems, cefazolin, cefoxitin and cefepime was observed. The stability of the NDM-1 and its mutants was explored by thermofluor assay in real-time PCR. The determination of TmB and TmD demonstrated that NDM-1 and L218T were the most stable enzymes. Molecular dynamic studies were performed to justify the differences observed in the kinetic behavior of the mutants. In particular, L218T fluctuated more than NDM-1 in L10, whereas L221T would seem to cause a drift between residues 75 and 125. L221T/Y229W double mutant exhibited a decrease in the flexibility with respect to L221T, explaining enzyme activity improvement towards some ß-lactams. Distances between Zn1-Zn2 and Zn1-OH- or Zn2-OH- remained unaffected in all systems analysed. Significant changes were found between Zn1/Zn2 and first sphere coordination residues.

Characterization of the First OXA-10 Natural Variant with Increased Carbapenemase Activity.

While carbapenem resistance in Gram-negative bacteria is mainly due to the production of efficient carbapenemases, ß-lactamases with a narrower spectrum may also contribute to resistance when combined with additional mechanisms. OXA-10-type class D ß-lactamases, previously shown to be weak carbapenemases, could represent such a case. In this study, two novel OXA-10 variants were identified as the sole carbapenem-hydrolyzing enzymes in meropenem-resistant enterobacteria isolated from hospital wastewater and found by next-generation sequencing to express additional ß-lactam resistance mechanisms. The new variants, OXA-655 and OXA-656, were carried by two related IncQ1 broad-host-range plasmids. Compared to the sequence of OXA-10, they both harbored a Thr26Met substitution, with OXA-655 also bearing a leucine instead of a valine in position 117 of the SAV catalytic motif. Susceptibility profiling of laboratory strains replicating the natural blaOXA plasmids and of recombinant clones expressing OXA-10 and the novel variants in an isogenic background indicated that OXA-655 is a more efficient carbapenemase. The carbapenemase activity of OXA-655 is due to the Val117Leu substitution, as shown by steady-state kinetic experiments, where the kcat of meropenem hydrolysis was increased 4-fold. In contrast, OXA-655 had no activity toward oxyimino-ß-lactams, while its catalytic efficiency against oxacillin was significantly reduced. Moreover, the Val117Leu variant was more efficient against temocillin and cefoxitin. Molecular dynamics indicated that Val117Leu affects the position 117-Leu155 interaction, leading to structural shifts in the active site that may alter carbapenem alignment. The evolutionary potential of OXA-10 enzymes toward carbapenem hydrolysis combined with their spread by promiscuous plasmids indicates that they may pose a future clinical threat.

Effect of ß-lactamase production and ß-lactam instability on MIC testing results for Mycobacterium abscessus.

OBJECTIVES: Limited treatment options available for Mycobacterium abscessus infections include the parenteral ß-lactam antibiotics cefoxitin and imipenem, which show moderate in vitro activity. Other ß-lactam antibiotics (except meropenem) have no considerable in vitro activity, due to their rapid hydrolysis by a broad-spectrum ß-lactamase (Bla_Mab). We here addressed the impact of ß-lactamase production and ß-lactam in vitro stability on M. abscessus MIC results and determined the epidemiological cut-off (ECOFF) values of cefoxitin, imipenem and meropenem. METHODS: By LC high-resolution MS (LC-HRMS), we assessed the in vitro stability of cefoxitin, imipenem and meropenem. M. abscessus ATCC 19977 strain and its isogenic blaMab deletion mutant were used for MIC testing. Based on MIC distributions for M. abscessus clinical strains, we determined ECOFFs of cefoxitin, imipenem and meropenem. RESULTS: A functional Bla_Mab increased MICs of penicillins, ceftriaxone and meropenem. LC-HRMS data showed significant degradation of cefoxitin, imipenem and meropenem during standard antibiotic susceptibility testing procedures. MIC, MIC50 and ECOFF values of cefoxitin, imipenem and meropenem are influenced by incubation time. CONCLUSIONS: The results of our study support administration of imipenem, meropenem and cefoxitin, for treatment of patients infected with M. abscessus. Our findings on in vitro instability of imipenem, meropenem and cefoxitin explain the problematic correlation between in vitro susceptibility and in vivo activity of these antibiotics and question the clinical utility of susceptibility testing of these chemotherapeutic agents.

Analysis of the Structure and Function of FOX-4 Cephamycinase.

Class C ß-lactamases poorly hydrolyze cephamycins (e.g., cefoxitin, cefotetan, and moxalactam). In the past 2 decades, a new family of plasmid-based AmpC ß-lactamases conferring resistance to cefoxitin, the FOX family, has grown to include nine unique members descended from the Aeromonas caviae chromosomal AmpC. To understand the basis for the unique cephamycinase activity in the FOX family, we determined the first X-ray crystal structures of FOX-4, apo enzyme and the acyl-enzyme with its namesake compound, cefoxitin, using the Y150F deacylation-deficient variant. Notably, recombinant expression of N-terminally tagged FOX-4 also yielded an inactive adenylylated enzyme form not previously observed in ß-lactamases. The posttranslational modification (PTM), which occurs on the active site Ser64, would not seem to provide a selective advantage, yet might present an opportunity for the design of novel antibacterial drugs. Substantial ligand-induced changes in the enzyme are seen in the acyl-enzyme complex, particularly the R2 loop and helix H10 (P289 to N297), with movement of F293 by 10.3 Å. Taken together, this study provides the first picture of this highly proficient class C cephamycinase, uncovers a novel PTM, and suggests a possible cephamycin resistance mechanism involving repositioning of the substrate due to the presence of S153P, N289P, and N346I substitutions in the ligand binding pocket.

New mutations in ADC-type ß-lactamases from Acinetobacter spp. affect cefoxitin and ceftazidime hydrolysis.

OBJECTIVES: Two natural variants of ADC-type ß-lactamases of Acinetobacter spp., ADC-1 and ADC-5, differ by nine mutations in their protein sequence. ADC-5 hydrolyses cefoxitin better than ADC-1 and the opposite is true for ceftazidime. We produced single and combined mutations in ADC-5 and characterized the variants microbiologically and biochemically to determine which amino acid residues are involved in the hydrolysis of ß-lactam antibiotics in this family of ß-lactamases. METHODS: Site-directed mutagenesis, with blaADC-5 as a source of DNA, was used to generate nine single mutated and three combined mutated enzymes. The proteins (wild-type and derivatives) were then expressed in isogenic conditions in Escherichia coli. MICs of ß-lactams were determined using Etest strips. ADC-1, ADC-5, ADC-5-P167S and ADC-5-P167S/D242G/Q163K/G342R were also purified and the kinetic parameters determined for ceftazidime, cefoxitin, cefalotin and ampicillin. RESULTS: Single mutations did not significantly convert the hydrolysis spectrum of the ADC-5 enzyme into that of the ADC-1 enzyme, although among all studied mutants only the quadruple mutant (ADC-5-P167S/D242G/Q163K/G342R) displayed microbiological and biochemical properties consistent with those of ADC-1. CONCLUSIONS: Although some single mutations are known to affect cefepime hydrolysis in ADC-type ß-lactamases, little is known about ceftazidime and cefoxitin hydrolysis in this family of ß-lactamases. Hydrolysis of these antibiotics appears to be positively and negatively affected, respectively, by the Q163K, P167S, D242G and G342R amino acid replacements.

N152G, -S, and -T substitutions in CMY-2 ß-lactamase increase catalytic efficiency for cefoxitin and inactivation rates for tazobactam.

Class C cephalosporinases are a growing threat, and clinical inhibitors of these enzymes are currently unavailable. Previous studies have explored the role of Asn152 in the Escherichia coli AmpC and P99 enzymes and have suggested that interactions between C-6' or C-7' substituents on penicillins or cephalosporins and Asn152 are important in determining substrate specificity and enzymatic stability. We sought to characterize the role of Asn152 in the clinically important CMY-2 cephalosporinase with substrates and inhibitors. Mutagenesis of CMY-2 at position 152 yields functional mutants (N152G, -S, and -T) that exhibit improved penicillinase activity and retain cephamycinase activity. We also tested whether the position 152 substitutions would affect the inactivation kinetics of tazobactam, a class A ß-lactamase inhibitor with in vitro activity against CMY-2. Using standard assays, we showed that the N152G, -S, and -T variants possessed increased catalytic activity against cefoxitin compared to the wild type. The 50% inhibitory concentration (IC50) for tazobactam improved dramatically, with an 18-fold reduction for the N152S mutant due to higher rates of enzyme inactivation. Modeling studies have shown active-site expansion due to interactions between Y150 and S152 in the apoenzyme and the Michaelis-Menten complex with tazobactam. Substitutions at N152 might become clinically important as new class C ß-lactamase inhibitors are developed.

Evaluation of cycloserine-cefoxitin fructose agar (CCFA), CCFA with horse blood and taurocholate, and cycloserine-cefoxitin mannitol broth with taurocholate and lysozyme for recovery of Clostridium difficile isolates from fecal samples.

Cycloserine-cefoxitin fructose agar (CCFA), CCFA with horse blood and taurocholate (CCFA-HT), and cycloserine-cefoxitin mannitol broth with taurocholate and lysozyme (CCMB-TAL) were compared for recovery of Clostridium difficile from 120 stool specimens. Compared to CCFA, CCFA-HT enhanced C. difficile growth and improved recovery by 4%. In a separate study, 9% (8/91) of stool samples previously C. difficile negative on plate medium were C. difficile positive when cultured in CCMB-TAL.

Isolation and characterization of Aeromonas schubertii from diseased snakehead, Channa maculata (Lacepède).

Pure bacterial cultures were isolated from diseased snakeheads, Channa maculata (Lacepède), suffering high mortality in a farm in Zhongshan, southern China. Three isolates, namely ZS20100725, ZS20100725-1 and ZS20100725-2, were identified as Aeromonas schubertii. All the isolates showed high 16S rRNA sequence similarities with A. schubertii. The isolates exhibited strong virulence to snakeheads in experimental challenges with LD(50) ranging between 1.4 × 10(4) and 6.4 × 10(6) CFU g(-1). Two of the isolates were positive for haemolysin, elastase, lipase and lecithinase by phenotypic determination, which was further confirmed by PCR amplification of the haemolysin and elastase genes. In sterile liquid medium, the best growth conditions of strain ZS20100725 were 30 °C, pH 7 and 0.5% salinity (w/v). Antibiotic susceptibility tests showed that strain ZS20100725 was susceptible to cefoxitin, cefoperazone and chloramphenicol. Furthermore, histopathology of diseased snakeheads infected with A. schubertii showed necrosis and congestion in liver, kidney and spleen and also damage to the cardiac muscle, intestine and gills.

Prevalence of Efflux Pump and Porin-Related Antimicrobial Resistance in Clinical Klebsiella pneumoniae in Baghdad, Iraq.

Klebsiella pneumoniae is an opportunistic bacterium that causes many infections, including septicemia, pneumonia, urinary tract infection, and liver abscesses. There are many mechanisms for antibiotic resistance and K. pneumonia is considered a multidrug-resistant pathogen. This study aimed to find the correlation between the susceptibility of K. pneumonia to certain antibiotics with the porin-related resistance and pumps mechanisms. In total, two genes that are responsible for porin formation were considered in the current study OmpK-35gene and OmpK-36 gene, in addition to other four genes (CfiaS, CfiaL, MFS, and MdtK genes) related to an efflux pump mechanism of antibiotic resistance. The bacterial resistance was investigated towards five cephalosporins (Cefazolin, Cefoxitin, Ceftazidime, Ceftriaxone, and Cefepime) and two carbapenems (imipenem and ertapenem). Clinical samples, including blood, swabs, and urine, consisting of 20 specimens for each group, were collected from patients who attended three hospitals in Baghdad. The VITEK-2 system and genetic tests (polymerase chain reaction and sequencing) of bacterial isolates were applied to confirm the diagnosis of K. pneumoniae and detect the antibiotic sensitivity profile. The results showed that 51 (85%) and 15 (25%) of the total 60 isolates had positive results for OmpK-35 and Omp-K36 genes, respectively. The MFS and MdtK genes were observed (70-88.3%) in cephalosporin-resistant isolates of K. pneumoniae. There were no significant variations of bacterial resistance genes of antibiotics within the specimen groups. It was concluded that the bacterial resistance of the selected antibiotics was elevated markedly with the loss of the OmpK-36 gene with a high expression of MFS and MdtK genes and a slight minimal occurrence in the new generation of carbapenems. The best antimicrobial agent was ertapenem with a percentage of 0% of resistance in all bacterial isolates.

Molecular analysis of the effector mechanisms of cefoxitin resistance among Bacteroides strains.

OBJECTIVES: The characterization of Bacteroides strains with regard to the cfxA gene, the MTn4555 mobilizable transposon, the role of penicillin-binding proteins (PBPs) and heterogeneous cefoxitin resistance. METHODS: Eighty-four randomly selected and 11 heterogeneously or highly cefoxitin-resistant Bacteroides isolates were included. Agar dilution and Etest methods were used for the determination of cefoxitin MICs. PCR experiments and nucleotide sequencing were used to detect the cfxA gene and the molecular features of MTn4555. Cefoxitin-binding experiments to determine its affinity (IC(50)) for PBPs and cefoxitinase assays were also applied. Southern blotting was used to determine the copy number of the cfxA genes. RESULTS: Sixteen strains from the random collection proved to be positive for cfxA, and the MIC distribution for the cfxA-negative and -positive strains did not display a clear separation. The majority of the cfxA-positive strains in this collection harboured a 1.2 kb common region at the 3' end of MTn4555. This region encoded an open reading frame that exhibited homology to abortive phage infection proteins (AbiD). The cfxA genes were transferable only at low frequencies in conjugation experiments. In PBP affinity studies, the PBP-A and PBP3 species were largely insensitive to cefoxitin, whereas the other PBP species were affected at very low concentrations. Seven of the heterogeneously resistant strains were positive for cfxA and most of them had mutations in the regulatory regions of cfxA. CONCLUSIONS: Major and minor roles for Bacteroides fragilis PBPs and the CfxA cefoxitinase, respectively, were inferred. The role of the newly recognized abiD may be to control the copy number of cfxA.

Crystal structures of covalent complexes of ß-lactam antibiotics with Escherichia coli penicillin-binding protein 5: toward an understanding of antibiotic specificity.

Penicillin-binding proteins (PBPs) are the molecular targets for the widely used ß-lactam class of antibiotics, but how these compounds act at the molecular level is not fully understood. We have determined crystal structures of Escherichia coli PBP 5 as covalent complexes with imipenem, cloxacillin, and cefoxitin. These antibiotics exhibit very different second-order rates of acylation for the enzyme. In all three structures, there is excellent electron density for the central portion of the ß-lactam, but weak or absent density for the R1 or R2 side chains. Areas of contact between the antibiotics and PBP 5 do not correlate with the rates of acylation. The same is true for conformational changes, because although a shift of a loop leading to an electrostatic interaction between Arg248 and the ß-lactam carboxylate, which occurs completely with cefoxitin and partially with imipenem and is absent with cloxacillin, is consistent with the different rates of acylation, mutagenesis of Arg248 decreased the level of cefoxitin acylation only 2-fold. Together, these data suggest that structures of postcovalent complexes of PBP 5 are unlikely to be useful vehicles for the design of new covalent inhibitors of PBPs. Finally, superimposition of the imipenem-acylated complex with PBP 5 in complex with a boronic acid peptidomimetic shows that the position corresponding to the hydrolytic water molecule is occluded by the ring nitrogen of the ß-lactam. Because the ring nitrogen occupies a similar position in all three complexes, this supports the hypothesis that deacylation is blocked by the continued presence of the leaving group after opening of the ß-lactam ring.

A tripeptide deletion in the R2 loop of the class C beta-lactamase enzyme FOX-4 impairs cefoxitin hydrolysis and slightly increases susceptibility to beta-lactamase inhibitors.

OBJECTIVES: A natural variant of the AmpC enzyme from Escherichia coli HKY28 with a tripeptide deletion (Gly-286/Ser-287/Asp-288) was recently described. The isolate produced an inhibitor-sensitive AmpC beta-lactamase variant that also conferred higher than usual levels of resistance to ceftazidime in the E. coli host. To demonstrate whether this is true in other class C beta-lactamase enzymes, we deleted the equivalent tripeptide in the FOX-4 plasmid-mediated class C beta-lactamase. METHODS: By site-directed mutagenesis, we deleted the tripeptide Gly-306/Asn-307/Ser-308 of FOX-4, thus generating FOX-4(DeltaGNS). The enzymes (FOX-4 wild-type and DeltaGNS) were purified and kinetic parameters (kcat, Km, kcat/Km) as well as IC50 values of several beta-lactams were assessed. Modelling studies were also performed. RESULTS: FOX-4(DeltaGNS) did not increase the catalytic efficiency towards ceftazidime, although it conferred a slight increase in the susceptibility to beta-lactamase inhibitors. There was also a noteworthy decrease in the cefoxitin MIC with the FOX-4(DeltaGNS) mutant (from 512 to 16 mg/L) as well as a 10-fold decrease in kcat/Km towards imipenem, which revealed specific structural features. CONCLUSIONS: Although deletions in the R2-loop are able to extend the substrate spectrum of class C enzymes, the present results do not confirm this hypothesis in FOX-4. The FOX-4 R2 site would already be wide enough to accommodate antibiotic molecules, and thus any amino acid replacement or deletion at this location would not affect the hydrolytic efficiency towards beta-lactams and would have a less drastic effect on the susceptibility to beta-lactamase inhibitors.

Binding of TEM-1 beta-lactamase to beta-lactam antibiotics by frontal affinity chromatography.

TEM-1 beta-lactamases can accurately catalyze the hydrolysis of the beta-lactam rings in beta-lactam antibiotics, which make beta-lactam antibiotics lose its activity, and the prerequisite for the hydrolysis procedure in the binding interaction of TEM-1 beta-lactamases with beta-lactam antibiotics is the beta-lactam rings in beta-lactam antibiotics. Therefore, the binding of TEM-1 beta-lactamase to three beta-lactam antibiotics including penicillin G, cefalexin as well as cefoxitin was explored here by frontal affinity chromatography in combination with fluorescence spectra, adsorption and thermodynamic data in the temperature range of 278-288K under simulated physiological conditions. The results showed that all the binding of TEM-1 beta-lactamase to the three antibiotics were spontaneously exothermic processes with the binding constants of 8.718×103, 6.624×103 and 2.244×103 (mol/L), respectively at 288K. All the TEM-1 beta-lactamases were immobilized on the surface of the stationary phase in the mode of monolayer and there existed only one type of binding sites on them. Each TEM-1 beta-lactamase bound with only one beta-lactam antibiotic and hydrogen bond interaction and Van der Waals force were the main forces between them. This work provided an insight into the binding interactions between TEM-1 beta-lactamases and beta-lactam antibiotics, which may be beneficial for the designing and developing of new substrates resistant to TEM-1 beta-lactamases.

Evaluation of a commercial immunochromatographic assay for rapid routine identification of PBP2a-positive Staphylococcus aureus and coagulase-negative staphylococci.

We evaluated the performance of an immunochromatographic assay (PBP2a Culture Colony Test - Alere™), detecting protein-binding penicillin 2a on staphylococci primary isolates in only 6minutes. The assay is highly sensitive for the direct detection of MRSA on various culture media whereas it requires cefoxitin induction for methicillin-resistant coagulase-negative staphylococci.

Interaction energies between beta-lactam antibiotics and E. coli penicillin-binding protein 5 by reversible thermal denaturation.

Penicillin-binding proteins (PBPs) catalyze the final stages of bacterial cell wall biosynthesis. PBPs form stable covalent complexes with beta-lactam antibiotics, leading to PBP inactivation and ultimately cell death. To understand more clearly how PBPs recognize beta-lactam antibiotics, it is important to know their energies of interaction. Because beta-lactam antibiotics bind covalently to PBPs, these energies are difficult to measure through binding equilibria. However, the noncovalent interaction energies between beta-lactam antibiotics and a PBP can be determined through reversible denaturation of enzyme-antibiotic complexes. Escherichia coli PBP 5, a D-alanine carboxypeptidase, was reversibly denatured by temperature in an apparently two-state manner with a temperature of melting (T(m)) of 48.5 degrees C and a van't Hoff enthalpy of unfolding (H(VH)) of 193 kcal/mole. The binding of the beta-lactam antibiotics cefoxitin, cloxacillin, moxalactam, and imipenem all stabilized the enzyme significantly, with T(m) values as high as +4.6 degrees C (a noncovalent interaction energy of +2.7 kcal/mole). Interestingly, the noncovalent interaction energies of these ligands did not correlate with their second-order acylation rate constants (k(2)/K'). These rate constants indicate the potency of a covalent inhibitor, but they appear to have little to do with interactions within covalent complexes, which is the state of the enzyme often used for structure-based inhibitor design.

Cefoxitin: a review of its antibacterial activity, pharmacological properties and therapeutic use.

Cefoxitin is a beta-lactam antibiotic derived from cephamycin C, a naturally occurring substance produced by Streptomyces lactamdurans. Its resistance to destruction by beta-lactamases results in a broad spectrum of antibacterial activity which includes anaerobic as well as Gram-positive and Gram-negative aerobic bacteria, including many resistant to cephalothin and other cephalosporins. Given by intravenous or intramuscular injection, cefoxitin is effective against a wide variety of infections caused by Gram-positive or Gram-negative aerobes as well as by anaerobic bacteria. It is generally well tolerated, thrombophlebitis, skin rash and some degree of discomfort after intramuscular injection, being the most commonly reported side effects. Cefoxitin has not been shown to cause adverse effects on renal function.

Penetration of clindamycin, cefoxitin, and piperacillin into pancreatic juice in man.

In our segmental pancreatic transplantation technique the pancreatic juice is temporarily diverted to the exterior via a pancreatic duct catheter. This permits studies on pure pancreatic juice to be carried out. In 11 such patients we studied the penetration of clindamycin, cefoxitin, and piperacillin into pancreatic juice. These three antibiotics all have good effect against the bacteria commonly isolated during pancreatic infections. Simultaneous blood and pancreatic juice samples were collected immediately before drug administration and at 30, 60, 90, and 120 minutes and 3, 4, 5, 6, and 8 hours after administration. The concentration of clindamycin in pancreatic juice was 34% of that in serum and exceeded the minimum inhibitory concentration for most bacteria associated with pancreatic infections. In spite of adequate serum concentrations of cefoxitin and piperacillin, the concentrations in pancreatic juice were only 8% and 5%, respectively, and did not exceed the minimum inhibitory concentration for the relevant bacteria. In view of these findings, clindamycin seems to be preferable in the treatment of pancreatic infections.

Cefoxitin serum and uterine concentrations following a two-gram intramuscular dose.

Two grams of cefoxitin was administered intramuscularly to 31 premenopausal women when they were called to the operating room for a scheduled vaginal hysterectomy. Serum and tissue samples were obtained to determine cefoxitin concentration. The mean concentration of cefoxitin at the reported peak in serum after an intramuscular injection (30 minutes) was 25.3 micrograms/ml. The mean serum concentration at the time of uterine excision (a mean of 143 minutes after the on-call dose) was 18.0 micrograms/ml. The mean concentrations of cefoxitin in the uterine fundus and the lower uterine segment at the time of uterine excision were 1.1 and 1.8 micrograms/g tissue, respectively.

Serum and tissue concentrations of cefoxitin and cefamandole in women undergoing hysterectomy.

To prevent infection in 40 patients who underwent vaginal or abdominal hysterectomy, each patient received a single 15-mg/kg dose of either cefoxitin or cefamandole by rapid (5-minute) intravenous injection before the operation. Samples of serum, myometrium, endometrium, ovaries, and tubes were obtained at various intervals after injection of the antibiotic and were assayed for cephalosporin concentration. Maximum tissue concentrations of 30 micrograms/g of both drugs were detected approximately 30 minutes after the dose, with levels dropping below 3 micrograms/g in approximately 2 hours. Although both antibiotics achieved closely similar concentrations in serum and tissues, the ratios of these levels to their usual mean minimum inhibitory concentrations for Bacteroides fragilis were appreciably higher for cefoxitin than for cefamandole. These pharmacokinetic observations support the current dosage recommendations for the use of cefoxitin in treating and preventing gynecologic infections, as well as the recommendation that it be administered shortly before the operation to maximize tissue levels during the perioperative period.